Advance polymer chemistry - Shan Chowdhury

Advance Polymer Chemistry
Ch-6105
# General survey of Polymers
1. Polymer - Polymer is a substance made up of a large number of smaller molecules that link together to formlarger
molecules. An example of a synthetic polymer is plastic. An example of a natural polymer is rubber.
A polymer is a large molecule made up of chains or rings of linked repeating subunits, which are called monomers.
Polymers usually have high melting and boiling points.Because themolecules consistofmany monomers, polymers tend
to have high molecular masses.
Example: Polymers may be divided into two categories. Natural polymers (also called biopolymers) include silk, rubber,
cellulose,wool,amber, keratin, collagen,starch,DNA,and shellac.Biopolymers serve key functions in organisms, acting
as structural proteins, functional proteins, nucleic acids, structural polysaccharides, and energy storage molecules.
Synthetic polymers are prepared by a chemical reaction, often in a lab. Examples of synthetic polymers include PVC
(polyvinylchloride),polystyrene,synthetic rubber,silicone, polyethylene, neoprene, and nylon. Synthetic polymers are
used to make plastics, adhesives, paints, mechanical parts, and many common objects.
Synthetic polymersmay be groupedinto two categories.Thermosetplastics are made from a liquid or soft solid substance
that can be irreversibly changedinto an insoluble polymerby curing usingheatorradiation.Thermoset plastics tend to be
rigid and have high molecularweights.The plastic stays out ofshape whendeformed and typically decompose before they
melt. Examples of thermoset plastics include epoxy, polyester, acrylic resins, polyurethanes, and vinyl esters. Bakelite,
Kevlar, and vulcanized rubber are also thermoset plastics.
Thermoplastic polymers orthermosoftening plastics are the othertypeofsynthetic polymers.While thermoset plastics are
rigid, thermoplastic polymers are solid when cool,but are pliable and can be molded above a certain temperature. While
thermoset plasticsformirreversible chemical bonds when cured,the bonding in thermoplastics weakens with temperature.
Unlike thermosets, which decompose rather than melt, thermoplastics melt into a liquid upon heating. Examples of
thermoplastics include acrylic, nylon, Teflon, polypropylene, polycarbonate, ABS, and polyethylene.
2. Oligomers:Dimers,trimers, and tetramers are,for example, oligomers respectively composed of two, three, and four
monomers. The oligomer is regarded as having an intermediate molecular weight if it has properties which do vary
significantly with the removal of one or a few of the units.
Examples: Collagen is an example of a homo-oligomeric protein that is composed of three identical protein chains. ...
Polybutene is an oligomeric oil used to make putty. Greek prefixes are often used to designate the number
of monomer units in the oligomer, for example a tetramer being composed of four units and a hexamer of six.
An oligomer is a molecular complex ofchemicals that consists of a few repeating units, in contrast to a polymer, where
the numberofmonomers is, in principle, infinite. Dimers, trimers, and tetramers are,forinstance,oligomers composed of
two, three, and four monomers, respectively.
In biochemistry, an oligomer usually refers to a macromolecular complex formed by non-covalent bonding of a few
macromolecules like proteins ornucleic acids.In this sense,a homo-oligomerwould be formed by few identicalmolecules
and by contrast,a hetero-oligomerwould be made of more than one,different,macromolecules. Collagen is an example of
a homo-oligomeric protein that is composedofthree identical protein chains. The term multimer is used with a meaning
similar to that of oligomer in the context of proteins (although technical restrictions of word sense may exist).
Many oils are oligomeric, such as liquid paraffin. Plasticizers are oligomeric esters widely used to
soften thermoplastics such as PVC. They may be made from monomers by linking themtogether, or by separation from
the higher fractions of crude oil. Polybutene is an oligomeric oil used to make putty. Greek prefixes are often used to
designate the number of monomer units in the oligomer, for example a tetramer being composed of four units and a
hexamer of six.
In biochemistry, the term oligonucleotide – or, informally, "oligo" – is used for short, single-stranded nucleic acid
fragments, such as DNA or RNA, or similar fragments of analogs of nucleic acids such as peptide nucleic
acid or Morpholinos.Such oligosare used in hybridization experiments (bound to glass slides or nylon membranes), as

probes for in situ hybridization or in antisense experiments such as gene knockdowns.[citation needed]
It can also refer to
a protein complexmade of two or more subunits. In this case, a complexmade of several different protein subunits is
called a hetero-oligomerorheteromer.When only one type ofprotein subunit is used in the complex, it is called a homo-
oligomer or homomer.
Oligomerizationis a chemicalprocess that converts monomers to macromolecular complexes through a finite degree of
polymerization. The actual figure for degree of polymerization is a matter of debate, often a value between 10 and 100.
Telomerization is the processwhere an oligomer forms a telomer as a result of chain transfer. A telomere is a region of
highly repetitive DNA at the end of a linear chromosome.
Green oil
In the oil and gas industry,green oilrefers to oligomers formed in all C2, C3, and C4 hydrogenation reactors of ethylene
plants and otherpetrochemicalproductionfacilities; it is a mixture ofC4 to C20 unsaturatedand reactive componentswith
about 90% aliphatic dienes and 10% ofolefins plus paraffins.[5]
Different heterogeneous and homogeneous catalysts are
operative in producing green oils via the oligomerization of olefins.
3. Monomer: Glucose,vinylchloride,amino acids,and ethylene areexamples of monomers. Each monomer may link in
different ways to forma variety of polymers.
Examples: A monomer is a molecule that forms the basic unit for polymers, which are the building blocks of proteins.
Monomers bind to other monomers to form repeating chain molecules through a process known as polymerization.
Monomers may be either natural or synthetic in origin.
Oligomers are polymers consistingofa small number(typically under100) of monomer subunits.Monomeric proteinsare
protein molecules that combine to form multi-protein complexes. Biopolymers are polymers consisting of organic
monomers found in living organisms.
Because monomers represent a huge classofmolecules,theyare commonly categorized into various subgroups such as
sugars, alcohols, amines, acrylics, and epoxides.
The term"monomer" combines the prefix mono-, which means "one," and the suffix-mer, which means "part."
Examples of Monomers
Glucose,vinylchloride, amino acids,and ethylene are examples of monomers. Each monomer may link in different ways
to form a variety of polymers. In the case of glucose, for example, glycosidic bonds may link sugar monomers to form
such polymers as glycogen, starch, and cellulose.
Names for Small Monomers
When only a few monomers combine to forma polymer, the compounds have names:
 Dimer: Polymer consisting of two monomers
 Trimer: Three monomer units
 Tetramer: Four monomer units
 Pentamer: Five monomer units
 Hexamer: Six monomer units
 Heptamer: Seven monomer units
 Octamer: Eight monomer units
 Nonamer: Nine monomer units
 Decamer: 10 monomer units
 Dodecamer: 12 monomer units
 Eicosamer: 20 monomer units

4. Macromolecules:There are fourbasic kinds of biological macromolecules. They are carbohydrates, lipids, proteins,
and nucleic acids. These polymers are composed of different monomers and serve different functions. ... Starch is an
example of a polysaccharide (many saccharides linked together) and is a formof stored glucose in plants.
Biological polymers are large molecules composed of many similar smaller molecules linked together in a chain-like
fashion.The individualsmaller molecules are called monomers. When small organic molecules are joined together, they
can form giant molecules or polymers.These giant molecules are also called macromolecules. Natural polymers are used
to build tissue and other components in living organisms.
Generally speaking,allmacromolecules are produced froma small set of about 50 monomers. Different macromolecules
vary because of the arrangement of these monomers. By varying the sequence, an incredibly large variety of
macromolecules can be produced. While polymers are responsible for the molecular "uniqueness" of an organism, the
common monomers mentioned above are nearly universal.
The variation in the form of macromolecules is largely responsible for molecular diversity. Much of the variation that
occurs both within an organism and among organisms can ultimately be traced to differences in macromolecules.
Macromolecules can vary from cell to cell in the same organism, as well as fromone species to the next.
A. Biomolecules:There are fourbasic kinds ofbiologicalmacromolecules.They are carbohydrates, lipids, proteins, and
nucleic acids. These polymers are composed of different monomers and serve different functions.
 Carbohydrates - molecules composed of sugar monomers. They are necessary for energy storage.
Carbohydrates are also called saccharides and their monomers are called monosaccharides. Glucose is an
important monosaccharide that is broken downduring cellularrespirationto be used as an energy source. Starch
is an example of a polysaccharide (many saccharides linked together) and is a formof stored glucose in plants.
 Lipids - water-insoluble molecules that can be classified as fats,phospholipids,waxes,and steroids. Fatty acids
are lipid monomers that consistof a hydrocarbon chain with a carboxyl group attached at the end. Fatty acids
form complex polymers suchas triglycerides,phospholipids, and waxes. Steroids are not considered true lipid
polymers because theirmolecules do not forma fatty acid chain. Instead, steroids are composed of four fused
carbon ring-like structures. Lipids help to store energy, cushion and protect organs, insulate the body, and
form cell membranes.
 Proteins - biomolecules capable offorming complex structures.Proteins are composedof amino acid monomers
and have a wide variety of functions including transportation of molecules and muscle movement. Collagen,
hemoglobin, antibodies, and enzymes are examples of proteins.
 Nucleic Acids - molecules consisting of nucleotide monomers linked together to form polynucleotide
chains. DNA and RNA are examples of nucleic acids. These molecules contain instructions for protein
synthesis and allow organisms to transfer genetic information fromone generation to the next.
B. Assembling andDisassembling Polymers:While there is variation among the types of biological polymers found in
different organisms, the chemical mechanisms for assembling and disassembling them are largely the same across
organisms.Monomers are generally linked togetherthrough a process called dehydration synthesis, while polymers are
disassembled through a process called hydrolysis. Both of these chemical reactions involve water. In dehydration
synthesis,bondsare formed linking monomers together while losing water molecules. In hydrolysis, the water interacts
with a polymer causing bonds that link monomers to each other to be broken.
C. Synthetic Polymers: Unlike naturalpolymers,which are found in nature,synthetic polymers are man-made. They are
derived frompetroleumoil and include products such as nylon, synthetic rubbers, polyester, Teflon, polyethylene, and
epoxy.Synthetic polymers have a number of uses and are widely used in household products. These products include
bottles, pipes, plastic containers, insulated wires, clothing, toys, and non-stick pans.
5.Degree of polymerization
The degree of polymerization, or DP, is the number of monomeric units in
a macromolecule or polymer or oligomer molecule.[1][2][3]

For a homopolymer,there is only one type ofmonomeric unit and the number-average degree of polymerization is given
by , where Mn is the number-average molecular weight and M0 is the molecular weight of the monomer unit. For
most industrialpurposes,degreesofpolymerization in the thousands ortens ofthousands are desired. This number does
not reflect the variation in molecule size of the polymer that typically occurs, it only represents the mean number of
monomeric units.
Some authors, however, define DP as the number of repeat units, where for copolymers the repeat unit may not be
identical to the monomeric unit.[4][5]
For example, in nylon-6,6, the repeat unit contains the two monomeric units —
NH(CH2)6NH— and —OC(CH2)4CO—, so that a chain of 1000 monomeric units corresponds to 500 repeat units. The
degree of polymerization or chain length is then 1000 by the first (IUPAC) definition, but 500 by the second.
Step-growth and chain-growth polymerization
In step-growth polymerization, in order to achieve a high degree of polymerization (and hence molecular weight), Xn, a
high fractional monomer conversion, p, is required, according to Carothers' equation For example, a monomer
conversion of p = 99% would be required to achieve Xn = 100.
For chain-growth free radicalpolymerization,however,Carothers'equation does notapply.Instead longchains are formed
from the beginningofthe reaction. Long reaction times increase the polymer yield, but have little effect on the average
molecular weight.[8]
The degree of polymerization is related to the kinetic chain length, which is the average number of
monomer molecules polymerized per chain initiated.[9]
However it often differs fromthe kinetic chain length for several
reasons:
 chain termination may occurwholly or partly by recombination of two chain radicals, which doubles the degree of
polymerization[10]
 chain transferto monomerstartsa newmacromolecule forthe same kinetic chain (of reaction steps), corresponding
to a decrease of the degree of polymerization
 chain transferto solvent or to another solute (a modifier or regulator also decreases the degree of polymerization
Correlation with physical properties
Polymers with identicalcompositionbut different molecularweights may exhibit different physicalproperties. In general,
increasing degree of polymerization correlates with higher melting temperature and higher mechanical strength.
Number-average and weight-average
Synthetic polymers invariably consist of a mixture of macromolecular species with different degrees of polymerization
and therefore ofdifferent molecularweights.There are different types ofaverage polymermolecularweight,which can be
measured in different experiments. The two most important are the number average (Xn) and the weight average (Xw).
The number-average degreeofpolymerization is a weighted mean of the degrees of polymerization of polymer species,
weighted by the mole fractions (orthe numberofmolecules)ofthe species.It is typically determined by measurements of
the osmotic pressure of the polymer.
The weight-average degree of polymerization is a weighted mean of the degrees of polymerization, weighted by
the weight fractions (or the overall weight of the molecules) of the species. It is typically determined by measurements
of Rayleigh light scattering by the polymer.
6. Polymerization: Chain-growth polymerization is involved in the manufacture of polymers such as polyethylene,
polypropylene, and polyvinyl chloride (PVC).
In polymerchemistry,polymerization is a process ofreacting monomermolecules together in a chemical reaction to form
polymer chains or three-dimensional networks.There are many forms of polymerization and different systems exist to
categorize them.
Introduction
In chemical compounds, polymerization can occur via a variety of reaction mechanisms that vary in complexity due to
the functional groups present in the reactants[4]
and their inherent steric effects. In more straightforward

polymerizations, alkenes form polymers through relatively simple radical reactions; in contrast, reactions involving
substitution at a carbonyl group require more complex synthesis due to the way in which reactants
polymerize.[4]
Alkanes can also be polymerized, but only with the help of strong acids.[5]
As alkenes can polymerize in somewhat straightforward radical reactions, they form useful compounds such
as polyethyleneand polyvinylchloride (PVC),[4]
which are producedin high tonnages eachyear[4]
due to their usefulness
in manufacturing processesofcommercial products,such as piping,insulation and packaging. In general, polymers such
as PVC are referred to as "homopolymers," as they consist of repeated long chains or structures of the same monomer
unit, whereas polymers that consist of more than one monomer unit are referred to as copolymers (or co-polymers).[6]
Othermonomer units,suchas formaldehydehydrates orsimple aldehydes,are able to polymerize themselves at quite low
temperatures (ca. −80 °C) to form trimers;[4]
molecules consisting of 3 monomer units, which can cyclize to form ring
cyclic structures,orundergofurther reactions to formtetramers,[4]
or 4 monomer-unit compounds. Such small polymers
are referred to as oligomers[4]
. Generally, because formaldehyde is an exceptionally reactive electrophile it
allows nucleophilic addition of hemiacetalintermediates, which are in general short-lived and relatively unstable "mid-
stage" compounds that react with other molecules present to formmore stable polymeric compounds.
Polymerization that is not sufficiently moderatedand proceeds at a fast rate can be very hazardous. This phenomenon is
known as hazardous polymerization and can cause fires and explosions.
Step-growth
There are two main classes of polymerization reaction mechanisms: step-growth and chain-growth. In step-growth (or
step)polymerization,each step may involve the combination of two polymer molecules of any lengths to forma longer
polymer molecule. The average molar mass increases slowly and long chains are formed only late in the reaction.[7][8]
.
Step-growth polymers are formed by independent reaction steps between functional groups of monomer units, usually
containing heteroatoms such as nitrogen or oxygen. Most step-growth polymers are also classified as condensation
polymers,since a small molecule such as wateris lost when the polymerchain is lengthened.Forexample, polyesterchains
grow by reaction of alcohol and carboxylic acid groups to form ester links with loss of water. However, there are
exceptions; for example polyurethanes are step-growth polymers formed from isocyanate and alcohol bifunctional
monomers)without loss ofwaterorothersmallmolecule, and are classified as addition polymers ratherthan condensation
polymers.
Step-growth polymers increase in molecular weight at a very slow rate at lower conversions and reach moderately high
molecular weights only at very high conversion (i.e., >95%).
Chain-growth
In chain-growth (or chain) polymerization, the only chain-extension reaction step is the addition of a monomer to a
growing chain with an active centersuch as a free radicalor ion.Once the growth ofa chain is initiated by formation of an
active center,chain propagationis usually rapid by additionofa sequence ofmonomers.Long chains are formed fromthe
beginning of the reaction.[7][8]
Chain-growth polymerization (oraddition polymerization)involves the linking togetherofmolecules incorporatingdouble
or triple carbon-carbon bonds. These unsaturated monomers (the identical molecules that make up the polymers) have
extra internalbonds that are able to break and link up with other monomers to forma repeating chain, whose backbone
typically contains only carbon atoms. Chain-growth polymerization is involved in the manufacture of polymers such
as polyethylene, polypropylene, and polyvinyl chloride (PVC). A special case of chain-growth polymerization leads
to living polymerization.
In the radicalpolymerization of ethylene,its π bondis broken,and thetwo electrons rearrangeto create a new propagating
center like the one that attacked it. The form this propagating center takes depends on the specific type of addition
mechanism.There are severalmechanisms through which this can be initiated. The free radical mechanismis one of the
first methods to be used. Free radicals are very reactive atoms or molecules that have unpaired electrons. Taking the
polymerization of ethylene as an example, the free radical mechanism can be divided into three stages: chain
initiation, chain propagation, and chain termination.
Polymerization of ethylene

Free radicaladdition polymerization ofethylene must take place at high temperatures and pressures,approximately 300 °C
and 2000 atm. While most otherfree radical polymerizations do not require suchextreme temperatures andpressures,they
do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs
randomly, when two chains collide, it is impossible to control the length of individual chains . A newer method of
polymerization similar to free radical, but allowing more control involves the Ziegler–Natta catalyst, especially with
respect to polymer branching.
Otherforms ofchain growth polymerization include cationic additionpolymerization and anionic additionpolymerization.
While not used to a large extent in industry yet due to stringent reaction conditions suchas lackofwaterand oxygen,these
methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such
as polypropylene.Cationic and anionic mechanisms are also more ideally suited for living polymerizations, although free
radical living polymerizations have also been developed.
Esters of acrylic acid contain a carbon-carbon double bond which is conjugated to an ester group. This allows the
possibility ofboth typesofpolymerization mechanism.An acrylic esterby itselfcan undergochain-growth polymerization
to form a homopolymerwith a carbon-carbon backbone,suchas poly(methylmethacrylate).Also,however,certain acrylic
esters can react with diamine monomers by nucleophilic conjugate addition ofamine groups to acrylic C=C bonds. In this
case the polymerization proceedsby step-growthand theproducts are poly(beta-amino ester)copolymers,with backbones
containing nitrogen (as amine) and oxygen (as ester) as well as carbon.
Physical polymer reaction engineering
To produce a high-molecular-weight, uniform product, various methods are employed to better control the initiation,
propagation,andtermination ratesduringchain polymerization and also to remove excess concentrated heat during these
exothermic reactions compared to polymerization of the pure monomer (also referred to as bulk polymerization). These
include emulsion polymerization,solutionpolymerization,suspension polymerization, and precipitation polymerization.
Althoughthe polymer polydispersity and molecular weight may be improved, these methods may introduce additional
processing requirements to isolate the product froma solvent.
6. Photopolymerization
Most photopolymerization reactions are chain-growthpolymerizations which are initiated by the absorption of visible[
or
ultraviolet light.The light may be absorbedeitherdirectly by the reactant monomer (direct photopolymerization), or else
by a photosensitizer which absorbs the light and thentransfers energy to the monomer. In general only the initiation step
differs from that ofthe ordinary thermalpolymerization ofthe same monomer; subsequent propagation, termination and
chain transfer steps are unchanged.In step-growth photopolymerization, absorption of light triggers an addition (or
condensation) reaction between two comonomers that do not react without light. A propagation cycle is not initiated
because each growth step requires the assistance of light.
Photopolymerization can be used asa photographic or printing process, because polymerization only occurs in regions
which have been exposed to light. Unreacted monomer can be removed from unexposed regions, leaving a relief
polymeric image.[11]
Severalforms of 3D printing—includinglayer-by-layerstereolithographyand two-photonabsorption
3D photopolymerization—use photopolymerization.
Multiphoton polymerization usingsingle pulses havealso beendemonstrated for fabrication of complexstructures using
a digital micromirror device.
7. High Polymer: A polymer is a large molecule,or macromolecule,composed ofmany repeatedsubunits.[6]
Due to their
broad range of properties,[7]
both synthetic and natural polymers play essential and ubiquitous roles in everyday
life.[8]
Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such
as DNA and proteins that are fundamentalto biologicalstructure and function. Polymers, both natural and synthetic, are
created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass,
relative to small molecule compounds,produces unique physical properties including toughness, viscoelasticity, and a
tendency to form glasses and semicrystalline structures rather than crystals. The terms polymer and resinare often
synonymous with plastic.
The term"polymer" derives fromthe Greek word πολύς andμέρος and refers to a molecule whose structure is composed
of multiple repeating units, from which originates a characteristic of high relative molecular mass and attendant
properties.[3]
The units composing polymers derive, actually or conceptually, frommolecules of low relative molecular
mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a definition distinct from the
modern IUPAC definition.[9][10]
The modern concept of polymers as covalently bonded macromolecular structures was
proposed in 1920 by Hermann Staudinger,[11]
who spent the next decade finding experimental evidence for this
hypothesis.[12]

Polymers are studied in the fields of biophysics and macromolecular science, and polymer science (which
includes polymer chemistry and polymer physics). Historically, products arising from the linkage of repeating units
by covalent chemicalbonds havebeenthe primary focus of polymerscience; emerging important areas ofthe science now
focus on non-covalent links. Polyisoprene of latexrubberis an example of a natural/biological polymer, and
the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts, essentially all
biologicalmacromolecules—i.e.,proteins (polyamides),nucleic acids(polynucleotides),and polysaccharides—are purely
polymeric, or are composed in large part of polymeric components—e.g., isoprenylated/lipid-modified glycoproteins,
where small lipidic molecules and oligosaccharide modifications occur on the polyamide backbone of the protein.[13]
The simplest theoretical models for polymers are ideal chains.
Common examples --See also: Polymer classes
Polymers are of two types: naturally occurring and synthetic or man made.
Naturalpolymeric materials such as hemp,shellac, amber,wool,silk, and naturalrubber have been used for centuries. A
variety of other natural polymers exist, such as cellulose, which is the main constituent of wood and paper.
The list ofsynthetic polymers,roughly in orderofworldwide demand,includes polyethylene,polypropylene,polystyrene,
polyvinyl chloride, synthetic rubber, phenol formaldehyde resin (or Bakelite), neoprene, nylon, polyacrylonitrile, PVB,
silicone, and many more. More than 330 million tons of these polymers are made every year (2015).
Most commonly,the continuously linked backbone of a polymer used for the preparation of plastics consists mainly of
carbon atoms.A simple example is polyethylene ('polythene'in British English),whose repeating unit is basedon ethylene
monomer. Many otherstructuresdo exist; forexample, elements such as silicon formfamiliar materials such as silicones,
examples being Silly Putty and waterproof plumbing sealant. Oxygen is also commonly present in polymer backbones,
such as those of polyethylene glycol, polysaccharides (in glycosidic bonds), and DNA (in phosphodiester bonds).
Synthesis
Main article: Polymerization
The repeating unit of the polymer polypropylene
Polymerization is the processofcombining many smallmolecules known as monomers into a covalently bonded chain or
network.During the polymerization process,some chemicalgroups may be lost fromeach monomer. This happens in the
polymerization of PET polyester. The monomers are terephthalic acid (HOOC—C6H4—COOH) and ethylene glycol
(HO—CH2—CH2—OH) but the repeating unit is —OC—C6H4—COO—CH2—CH2—O—, which corresponds to the
combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is
incorporated into the polymer is known as a repeat unit or monomer residue.
Laboratory synthetic methods are generally divided into two categories, step-growth polymerization and chain-growth
polymerization.[15] The essentialdifference between thetwo is that in chain growth polymerization,monomers are added
to the chain one at a time only,[16] such as in polyethylene, whereas in step-growth polymerization chains of monomers
may combine with one anotherdirectly,[17]such as in polyester.Newermethods,such as plasma polymerization do not fit
neatly into eithercategory.Synthetic polymerization reactions may be carried out with or without a catalyst. Laboratory
synthesis of biopolymers, especially of proteins, is an area of intensive research.
Biological synthesis--- Main article: Biopolymer
Microstructure of part of a DNA double helix biopolymer
There are three main classes ofbiopolymers:polysaccharides,polypeptides,andpolynucleotides.In living cells, they may
be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase. The
synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information fromthe DNA to
RNA and subsequently translate that information to synthesize the specified protein fromamino acids.The protein may be

modified further following translation in order to provide appropriate structure and functioning. There are other
biopolymers such as rubber, suberin, melanin, and lignin.
Modification of natural polymers
Naturally occurring polymers such as cotton, starch, and rubber were familiar materials for years before synthetic
polymers such aspolyethene and perspexappearedon the market.Many commercially important polymers are synthesized
by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and
cellulose to formnitrocellulose and theformation ofvulcanized rubberby heating naturalrubberin the presence of sulfur.
Ways in which polymers can be modified include oxidation, cross-linking, and endcapping.
Especially in the production of polymers the gas separation by membranes has acquired increasing importance in the
petrochemical industry and is now a relatively well-established unit operation. The process of polymer degassing is
necessary to suit polymer for extrusion and pelletizing, increasing safety, environmental, and product quality aspects.
Nitrogen is generally used forthis purpose, resulting in a vent gas primarily composed of monomers and nitrogen.[18]
Properties
Polymer properties are broadly divided into severalclasses based on the scale at which the property is defined as well as
upon its physicalbasis.[19]The most basic property ofa polymeris the identity ofits constituent monomers.A secondset
of properties,known as microstructure,essentially describes the arrangementofthesemonomers within the polymerat the
scale ofa single chain.These basic structural properties play a major role in determining bulk physical properties of the
polymer, which describe how the polymer behaves as a continuous macroscopic material. Chemical properties, at the
nano-scale,describe howthe chainsinteractthrough various physical forces. At the macro-scale, they describe how the
bulk polymer interacts with other chemicals and solvents.
Monomers and repeat units
The identity of the repeat units (monomer residues, also known as "mers") comprising a polymer is its first and most
important attribute.Polymernomenclature is generally basedupon thetypeofmonomerresidues comprising the polymer.
Polymers which contain only a single type ofrepeatunit are known as homopolymers, while polymers containing two or
more types of repeat units are known as copolymers.[20] Terpolymers contain three types of repeat units.[21]
Poly(styrene)is composed only ofstyrene monomerresidues,and is classified as a homopolymer. Ethylene-vinyl acetate
containsmore than one varietyofrepeat unit and is a copolymer.Some biological polymers are composed of a variety of
different but structurally related monomerresidues; forexample, polynucleotides such as DNA are composedoffourtypes
of nucleotide subunits.
A polymer molecule containing ionizable subunits is known as a polyelectrolyte or ionomer.
Microstructure-- Main article: Microstructure
The microstructure of a polymer (sometimes called configuration) relates to the physical arrangement of monomer
residues alongthe backboneofthe chain.[22] These are the elements of polymer structure that require the breaking of a
covalent bond in orderto change.Structure hasa strong influenceon the other properties of a polymer. For example, two
samples of natural rubber may exhibit different durability, even though their molecules comprise the same monomers.
Polymer architecture-- Main article: Polymer architecture
Branch point in a polymer
An important microstructuralfeature ofa polymeris its architecture andshape,which relates to theway branchpointslead
to a deviation froma simple linear chain.[23] A branched polymermolecule is composed ofa main chain with one ormore

substituent side chainsorbranches.Typesofbranched polymers include starpolymers,comb polymers,polymer brushes,
dendronized polymers,ladderpolymers,and dendrimers.[23]There exist also two-dimensional polymers (2DP) which are
composed oftopologically planarrepeatunits.A polymer's architecture affects many of its physical properties including,
but not limited to,solution viscosity,melt viscosity,solubility in various solvents,glass transitiontemperature and the size
of individualpolymercoils in solution.A variety oftechniques may be employed forthe synthesis of a polymeric material
with a range of architectures, for example living polymerization.
Chain length
A common means of expressing the length of a chain is the degree of polymerization, which quantifies the number of
monomers incorporated into thechain.[24][25]As with other molecules, a polymer's size may also be expressed in terms
of molecular weight.Since synthetic polymerization techniques typically yield a statistical distribution of chain lengths,
the molecularweight is expressed in terms ofweighted averages.The number-average molecularweight (Mn)and weight-
average molecular weight (Mw) are most commonly reported.[26][27] The ratio of these two values (Mw / Mn) is the
dispersity (Đ), which is commonly used to express the width of the molecular weight distribution.
The physical properties[29] of polymer strongly depend on the length (or equivalently, the molecular weight) of the
polymer chain.[30] One important example of the physical consequences of the molecular weight is the scaling of the
viscosity (resistance to flow) in the melt.[31] The influence of the weight-average molecular weight (Mw) on the melt
viscosity (η) depends on whether the polymer is above or below the onset of entanglements. Below the entanglement
molecular weight[clarification needed], {displaystyle eta,sim{M_{w}}^{1}} {displaystyle eta,sim{M_{w}}^{1}},
whereas above the entanglement molecular weight, {displaystyle eta,sim{M_{w}}^{3.4}} {displaystyle
eta,sim{M_{w}}^{3.4}}. In the lattercase,increasing thepolymerchain length10-fold would increase the viscosity over
1000 times.[32][page needed]Increasing chain lengthfurthermore tends to decrease chain mobility,increase strength and
toughness,andincrease the glasstransitiontemperature (Tg).[33]This is a result ofthe increase in chain interactions such
as Van derWaals attractionsand entanglements that come with increasedchain length.[34][35]These interactions tend to
fix the individualchains more strongly in position andresistdeformations and matrixbreakup,both at higherstresses and
higher temperatures.
Monomer arrangement in copolymers-- Main article: Copolymer
Different types of copolymers
Monomers within a copolymer may be organized along the backbone in a variety of ways. A copolymer containing a
controlled arrangement of monomers is called a sequence-controlled polymer.[36] Alternating, periodic and block
copolymers are simple examples of sequence-controlled polymers.
Alternating copolymers possess two regularly alternating monomer residues [AB]n (structure 2 at right). An example is
the equimolar copolymer of styrene and maleic anhydride formed by free-radical chain-growth polymerization.A step-
growth copolymer such as Nylon 66 can also be considered a strictly alternating copolymer of diamine and diacid
residues,but is often described as a homopolymer with the dimeric residue of one amine and one acid as a repeat unit.
Periodic copolymers have monomer residue types arranged in a repeating sequence: [AnBm...] mbeing different from
n.[citation needed]

Statisticalcopolymershave monomerresiduesarrangedaccording to a statisticalrule.A statisticalcopolymerin which the
probability offinding a particulartype ofmonomerresidue at a particularpoint in the chain is independent of the types of
surrounding monomer residue may be referred to as a truly random copolymer[40][41] (structure 3). For example, the
chain-growth copolymer of vinyl chloride and vinyl acetate is random.
Block copolymers have long sequencesofdifferent monomerunits (structure 4).Polymers with two orthree blocks of two
distinct chemicalspecies(e.g.,A and B) are called diblock copolymers and triblock copolymers, respectively. Polymers
with three blocks, each of a different chemical species (e.g., A, B, and C) are termed triblock terpolymers.
Graft or grafted copolymers contain side chains or branches whose repeat units have a different composition or
configuration than the main chain.[39] (structure 5) The branches are added on to a preformed main chain
macromolecule.[38]
Tacticity-- Main article: Tacticity
Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule.
There are three types oftacticity:isotactic (allsubstituents on the same side),atactic (randomplacement of substituents),
and syndiotactic (alternating placement of substituents).
Morphology
Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space.
Crystallinity
When applied to polymers,the termcrystalline has a somewhat ambiguous usage.In some cases,the termcrystalline finds
identical usage to that used in conventional crystallography. For example, the structure of a crystalline protein or
polynucleotide,suchas a sample prepared for x-ray crystallography, may be defined in terms of a conventional unit cell
composed ofone ormore polymermolecules with cell dimensions ofhundreds ofangstroms ormore.A synthetic polymer
may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than
macromolecular) length scales,usually arising fromintramolecularfolding and/or stacking of adjacent chains. Synthetic
polymers may consist ofbothcrystalline and amorphous regions; the degree ofcrystallinity may be expressedin terms ofa
weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline.[42] The
crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-
crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are
generally tougher(can be bentmore without breaking) and more impact-resistant than totally amorphous polymers.[43]
Polymers with a degree of crystallinity approaching zero or one will tend to be transparent, while polymers with
intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For
many polymers, reduced crystallinity may also be associated with increased transparency.

Chain conformation
The space occupied by a polymer molecule is generally expressed in terms of radius of gyration, which is an average
distance fromthe centerofmass ofthe chain to the chain itself. Alternatively, it may be expressed in terms of pervaded
volume, which is the volume of solution spanned by the polymer chain and scales with the cube of the radius of
gyration.[44]
Mechanical properties
A polyethylene sample that has necked under tension.
The bulk propertiesofa polymerare those most often of end-use interest. These are the properties that dictate how the
polymer actually behaves on a macroscopic scale.
Tensile strength
The tensile strength of a material quantifies how much elongating stress the material will endure before failure.[45][46]
This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber
band with a highertensile strengthwill hold a greaterweight before snapping. In general, tensile strength increases with
polymer chain length and crosslinking of polymer chains.
Young's modulus of elasticity
Young's modulus quantifies theelasticity of the polymer. It is defined, for small strains, as the ratio of rate of change of
stressto strain.Like tensile strength,this is highly relevant in polymer applications involving the physical properties of
polymers,such as rubberbands.The modulusis strongly dependent on temperature. Viscoelasticity describes a complex
time-dependent elastic response, which will exhibit hysteresis in the stress -strain curve when the load is removed.
Dynamic mechanicalanalysisorDMA measures this complexmodulus by oscillating the load andmeasuringthe resulting
strain as a function of time.
Transport properties
Transportpropertiessuch asdiffusivitydescribe howrapidly molecules move throughthe polymer matrix. These are very
important in many applications of polymers for films and membranes.
The movement of individual macromolecules occurs by a process called reptation in which each chain molecule is
constrained byentanglementswith neighboring chains to move within a virtual tube. The theory of reptation can explain
polymer molecule dynamics and viscoelasticity.
Phase behavior-- Crystallization andmelting
Thermal transitionsin (A)amorphousand (B)semicrystalline polymers,represented as traces fromdifferential scanning
calorimetry. As the temperature increases,both amorphous and semicrystalline polymers go through the glass transition
(Tg). Amorphous polymers (A) do not exhibit other phase transitions, though semicrystalline polymers (B) undergo
crystallization and melting (at temperatures Tc and Tm, respectively).

Depending on theirchemicalstructures,polymers may be eithersemi-crystalline oramorphous.Semi-crystalline polymers
can undergocrystallization and melting transitions,whereas amorphous polymers do not. In polymers, crystallization and
melting do not suggest solid-liquid phase transitions, as in the case of water or other molecular fluids. Instead,
crystallization and melting referto the phase transitions between two solid states (i.e., semi-crystalline and amorphous).
Crystallization occurs above the glass transition temperature (Tg) and below the melting temperature (Tm).
Glass transition
All polymers (amorphous or semi-crystalline) go through glass transitions. The glass transition temperature (Tg) is a
crucial physicalparameterforpolymermanufacturing,processing, and use. Below Tg, molecular motions are frozen and
polymers are brittle and glassy.Above Tg, molecular motions are activated and polymers are rubbery and viscous. The
glass transition temperature may be engineeredby altering thedegreeofbranching orcrosslinking in the polymerorby the
addition of plasticizers.
Whereascrystallization and melting are first-orderphase transitions, the glass transition is not.[49] The glass transition
shares featuresofsecond-orderphase transitions (such as discontinuity in the heat capacity,as shown in the figure), but it
is generally not considered a thermodynamic transition between equilibriumstates.
Mixing behavior
Phase diagram of the typical mixing behavior of weakly interacting polymer solutions, showing spinodal curves and
binodal coexistence curves.
In general,polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results fromthe
fact that the driving force formixing is usually entropy,not interactionenergy.In other words, miscible materials usually
form a solution not because theirinteraction with each otheris more favorable than theirself-interaction,but because ofan
increase in entropy andhence free energyassociated with increasingthe amount of volume available to each component.
This increase in entropyscales with the numberofparticles (or moles) being mixed. Since polymeric molecules are much
larger and hence generally havemuch higherspecific volumes than smallmolecules,the numberofmolecules involved in
a polymeric mixture is far smaller than the numberin a small molecule mixture of equalvolume.The energetics of mixing,
on the otherhand,is comparable on a pervolume basis forpolymeric and small molecule mixtures. This tends to increase
the free energy of mixing for polymer solutions and thereby making solvation less favorable, and thereby making the
availability of concentrated solutions of polymers far rarer than those of small molecules.

Furthermore,the phasebehaviorofpolymersolutions andmixtures is more complex than that of small molecule mixtures.
Whereasmost smallmolecule solutionsexhibit only an uppercriticalsolution temperature phase transition,at which phase
separationoccurswith cooling,polymermixtures commonly exhibit a lower critical solution temperature phase transition,
at which phase separation occurs with heating.
In dilute solution,the propertiesofthe polymerare characterized by the interaction between the solvent and the polymer.
In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces
between the solvent andmonomersubunitsdominate over intramolecular interactions. In a bad solvent or poor solvent,
intramolecularforces dominate and the chain contracts.In the thetasolvent,orthe state ofthe polymersolution where the
value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the
intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer
behaves like an ideal randomcoil. The transition between the states is known as a coil–globule transition.
Inclusion of plasticizers
Inclusion ofplasticizers tendsto lowerTg and increase polymer flexibility. Plasticizers are generally small molecules that
are chemically similar to the polymerand create gaps between polymerchains forgreatermobility and reduced interchain
interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or
unplasticized polyvinylchloride,is usedforthings such as pipes.A pipe has no plasticizers in it, because it needs to remain
strong andheat-resistant.Plasticized PVC is used in clothing fora flexible quality. Plasticizers are also put in some types
of cling film to make the polymer more flexible.
Chemical properties
The attractive forces between polymer chains play a large part in determining polymer's properties. Because polymer
chains are so long, these interchain forces are amplified far beyond the attractions between conventional molecules.
Different side groupson thepolymercan lend the polymerto ionic bonding orhydrogen bondingbetween its own chains.
These stronger forces typically result in higher tensile strength and higher crystalline melting points.
The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or
carbonylgroupscan formhydrogen bondsbetween adjacent chains; the partially positively charged hydrogen atoms in N-
H groups ofone chain are strongly attracted to the partially negatively charged oxygen atoms in C=O groups on another.
These stronghydrogenbonds, for example, result in the high tensile strength and melting point of polymers containing
urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the
hydrogenatomsin H-C groups.Dipole bonding is not as strongas hydrogen bonding, so a polyester's melting point and
strength are lower than Kevlar's (Twaron), but polyesters have greater flexibility.
Ethene,however,has nopermanent dipole. The attractive forces between polyethylene chains arise fromweak Van der
Waals forces.Moleculescan be thought ofas being surrounded by a cloud of negative electrons. As two polymer chains
approach,their electron clouds repel one another. This has the effect of lowering the electron density on one side of a
polymerchain,creating a slight positive dipole on this side. This charge is enough to attract the second polymer chain.

Van der Waals forces are quite weak,however,so polyethylene can have a lower melting temperature compared to other
polymers.
Optical properties
Polymers such as PMMAand HEMA:MMAare usedas matrices in the gain mediumof solid-statedye lasers,also known
as solid-state dye-doped polymerlasers.These polymers have a high surfacequality andare also highly transparentso that
the laserproperties are dominated by thelaserdye usedto dope the polymermatrix. These type oflasers,that also belong
to the class oforganic lasers,are known to yield very narrow linewidths which is useful for spectroscopy and analytical
applications.[50]An important opticalparameterin the polymerused in laserapplications is the change in refractive index
with temperature also known asdn/dT.Forthe polymers mentionedhere the (dn/dT) ~ −1.4 × 10−4 in units of K−1 in the
297 ≤ T ≤ 337 K range.
Standardized nomenclature
There are multiple conventionsfornaming polymersubstances.Many commonly used polymers, such as those found in
consumerproducts,are referred to by a common or trivial name.The trivial name is assigned based on historicalprecedent
or popular usage rather than a standardized naming convention. Both the American Chemical Society (ACS)[52] and
IUPAC[53] have proposed standardized naming conventions; the ACS and IUPAC conventions are similar but not
identical.[54] Examples of the differences between the various naming conventions are given in the table below:
Common name ACS name IUPAC name
Poly(ethylene oxide) or PEO Poly(oxyethylene)Poly(oxyethene)
Poly(ethylene terephthalate) or PET Poly(oxy-1,2-ethanediyloxycarbonyl-1,4-phenylenecarbonyl)
Poly(oxyetheneoxyterephthaloyl)
Nylon 6 Poly[amino(1-oxo-1,6-hexanediyl)] Poly[amino(1-oxohexan-1,6-diyl)]
In both standardized conventions, the polymers' names are intended to reflect the monomer(s) from which they are
synthesized ratherthan the precise nature ofthe repeatingsubunit. For example, the polymer synthesized fromthe simple
alkene ethene is called polyethylene, retaining the -ene suffix even though the double bond is removed during the
polymerization process:
Ethene polymerization.png→Polyethylene-repeat-2D-flat.png
Characterization-- Main article: Polymer characterization
Polymer characterization spans many techniques fordetermining the chemicalcomposition,molecularweight distribution,
and physical properties. Select common techniques include the following:
Size-exclusion chromatography (also called gel permeation chromatography), sometimes coupled with static light
scattering,can used to determine the number-average molecularweight,weight-average molecularweight,and dispersity.
Scattering techniques, such as static light scattering and small-angle neutron scattering, are used to determine the
dimensions (radius of gyration) of macromolecules in solution or in the melt. These techniques are also used to
characterize the three-dimensional structure of microphase-separated block polymers, polymeric micelles, and other
materials.
Wide-angle X-ray scattering (also called wide-angle X-ray diffraction) is used to determine the crystalline structure of
polymers (or lack thereof).

Spectroscopytechniques,includingFourier-transforminfrared spectroscopy,Raman spectroscopy, and nuclear magnetic
resonance spectroscopy, can be used to determine the chemical composition.
Differential scanningcalorimetry is used to characterize the thermal properties of polymers, such as the glass transition
temperature,crystallization temperature,and melting temperature.The glass transitiontemperature can alsobe determined
by dynamic mechanical analysis.
Thermogravimetry is a useful technique to evaluate the thermal stability of the polymer.
Rheology is usedto characterize the flowand deformation behavior. It can be used to determine the viscosity, modulus,
and otherrheologicalproperties.Rheologyis also often used to determine the molecular architecture (molecular weight,
molecular weight distribution, branching) and to understand how the polymer can be processed.
Degradation--- Main article: Polymer degradation
A plastic itemwith thirty years ofexposure to heatand cold,brake fluid,and sunlight. Notice the discoloration, swelling,
and crazing of the material.
Polymer degradationis a change in the properties—tensile strength, color, shape, or molecular weight—of a polymer or
polymer-basedproductunder the influence of one or more environmental factors, such as heat, light, chemicals and, in
some cases,galvanic action.It is often due to the scission ofpolymerchain bonds via hydrolysis, leading to a decrease in
the molecular mass of the polymer. Although such changes are frequently undesirable, in some cases, such as
biodegradationand recycling,theymay be intendedto preventenvironmentalpollution.Degradation canalso be useful in
biomedical settings. For example, a copolymer of polylactic acid and polyglycolic acid is employed in hydrolysable
stitchesthatslowly degrade afterthey are applied to a wound. The susceptibility ofa polymer to degradation depends on
its structure.Epoxies and chains containing aromatic functionalities are especially susceptible to UVdegradation while
polyesters are susceptible to degradation by hydrolysis,while polymers containing an unsaturated backboneare especially
susceptible to ozone cracking. Carbon based polymers are more susceptible to thermal degradation than in organic
polymers such as polydimethylsiloxane and are therefore not ideal for most high-temperature applications. High-
temperature matrices such as bismaleimides (BMI), condensation polyimides (with an O-C-N bond), triazines (with a
nitrogen (N)containing ring),and blends thereofare susceptible to polymerdegradationin the formof galvanic corrosion
when bare carbon fiber reinforced polymer CFRP is in contact with an active metal such as aluminium in salt water
environments.
The degradation of polymers to form smaller molecules may proceed by random scission or specific scission. The
degradation of polyethylene occurs by randomscission—a randombreakage of the bonds that hold the atoms of the
polymertogether.When heated above450 °C, polyethylene degrades to forma mixture of hydrocarbons. Other polymers,
such as poly(alpha-methylstyrene),undergo specific chain scissionwith breakage occurringonly at the ends.They literally
unzip or depolymerize back to the constituent monomer.The sorting of polymer waste for recycling purposes may be
facilitated by the use ofthe resin identificationcodes developed bythe Societyofthe Plastics Industry to identify the type
of plastic.
Product failure
In a finished product,such a change is to be prevented ordelayed.Failure ofsafety-criticalpolymercomponents cancause
serious accidents,such as fire in the case ofcracked and degradedpolymer fuellines.Chlorine-induced cracking ofacetal
resin plumbing joints and polybutylene pipes has causedmany serious floods in domestic properties,especially in the US
in the 1990s. Traces ofchlorine in the watersupply attacked vulnerable polymers in the plastic plumbing,a problemwhich
occurs fasterifany of the parts have beenpoorly extruded orinjection molded.Attackofthe acetaljoint occurred because
of faulty molding,leading to cracking along the threads ofthe fitting which is a serious stress concentration.

Ozone-induced crackingin naturalrubbertubing
Polymer oxidation has caused accidents involving medical devices. One of the oldest known failure modes is ozone
cracking causedby chain scissionwhen ozone gas attacks susceptible elastomers,suchas naturalrubberand nitrile rubber.
They possessdouble bonds in theirrepeat units which are cleavedduring ozonolysis.Cracks in fuel lines can penetrate the
bore of the tube and cause fuel leakage. If cracking occurs in the engine compartment, electric sparks can ignite
the gasoline and can cause a serious fire. In medical use degradation of polymers can lead to changes of physical and
chemical characteristics of implantable devices.
Fuel lines can also be attacked byanotherformof degradation:hydrolysis. Nylon 6,6is susceptible to acid hydrolysis,and
in one accident,a fractured fuelline led to a spillage of dieselinto the road.If dieselfuel leaks onto the road, accidents to
following cars can be caused by the slippery nature of the deposit, which is like black ice. Furthermore, the asphalt
concrete road surface will suffer damage as a result of the diesel fuel dissolving the asphaltenes fromthe composite
material, this resulting in the degradation of the asphalt surface and structural integrity of the road.
## Classify polymers from different point of view?
Polymer Chemistry:ClassificationofPolymers.The most common way of classifying polymers is to separatetheminto
three groups -thermoplastics,thermosets,and elastomers.The thermoplastics can be dividedinto two types -thosethatare
crystalline and those that are amorphous.
The most common way of classifying polymers is to separate them into three groups - thermoplastics, thermosets,
and elastomers.The thermoplastics canbe divided into two types -those that are crystalline and those thatare amorphous.
Thermoplastics
Molecules in a thermoplastic are held togetherby relatively weakintermolecularforces so that the material softens when
exposed to heat andthenreturnsto its originalcondition whencooled.Thermoplastic polymers can be repeatedly softened
by heating and then solidified by cooling -a process similar to the repeatedmelting and cooling ofmetals.Mostlinearand
slightly branched polymers are thermoplastic. All the major thermoplastics are produced by chain polymerization.
Thermoplastics have a wide range of applications because they can be formed and reformed in so many shapes. Some
examples are food packaging, insulation, automobile bumpers, and credit cards.
Thermosets

A thermosettingplastic, orthermoset,solidifies or"sets" irreversibly when heated; they cannot be reshaped by heating.
Thermosetsusually are three-dimensionalnetworked polymers in which there is a high degree of cross-linking between
polymer chains. The cross-linking restricts the motion of the chains and leads to a rigid material. A simulated skeletal
structure of a network polymer with a high cross-link density is shown below.
Thermosetsare strong anddurable.They primarily are used in automobiles and construction. They also are used to make
toys, varnishes, boat hulls, and glues.
Elastomers
Elastomers are rubbery polymers thatcan be stretched easily to several times their unstretched length and which rapidly
return to theiroriginaldimensions when the applied stress is released.Elastomers are cross-linked, but have a low cross-
link density.The polymerchains stillhave some freedomto move,but are prevented frompermanently moving relative to
each otherby the cross-links.To stretch,the polymer chains must not be part of a rigid solid - either a glass or a crystal.
An elastomermust be aboveits glasstransitiontemperature, TgTg,and have a low degree of crystallinity. Rubber bands
and other elastics are made of elastomers.
## Define organic and inorganic polymer with example of eachpolymer with their structural formulas?
Unlike organic polymers,inorganic polymers do not have carbon-carbonbonds in theirpolymerbackbone.Organic
polymers,examples : Silicon, sulphur,nitrogen,phosphorus & boron are the most common non-carbonelements forming
inorganic polymers orcatenatedcompounds.
Organic compounds andinorganic compoundsformthe basis ofchemistry.The primary difference between organic
compounds andinorganic compoundsis thatorganic compounds always contain carbon while most inorganic compounds

do not contain carbon(but there are a few that do).Also,nearly allorganic compounds contain carbon-hydrogenorC-H
bonds.
Organic compounds are molecules associatedwith living organisms. Theseinclude carbohydrates,lipids,nucleic acids,
proteins,enzymes,andhydrocarbon fuels.Organic compounds are broadly classified as naturaland synthetic compounds.
Further,they are subdividedby the presence ofheteroatoms,suchas organometallic (carbon atoms bondedto metals)and
organophosphorouscompounds(carbon atoms bonded to phosphorous).They are also classified as smallmolecules or
large macromolecules (polymers)based ontheirsize.Organic naturalcompounds are derived fromplants and animals and
include primary metabolites,such as sugarsand carbohydrates,fats and lipids,peptides andproteins,nucleic acids,and a
whole range ofsecondary metabolitessuch asalkaloids,flavonoids,terpenoids,and vitamins.Synthetic compounds are
chemically synthesized by reaction ofcompounds.Most polymers (a category that includes allplastics and rubbers)are
organic,synthetic,orsemi-synthetic compounds.Generally,organic compounds possess carbon–carbon bonds,carbon–
hydrogenbonds,as wellas covalent bonds betweencarbon andoxygen,and nitrogen.
Examples of some organic compounds:leucine,sphingolipids,palmitic acid, sucrose,glycogen,DNA,glutathione,
diosgenin,caffeine,morphine,and so on.
Inorganic compoundsare compounds which do not contain carbonandare not derived fromliving matter. They include
substancesmade fromsingle elements,salts,metals,and any othercompound that do not contain carbonbonded to
hydrogen.Generally,inorganic compoundsare derived fromgeologicalsystems,such as sediments and ores.Inorganic
compounds are not covalently bondedandexhibit ionic characters.Due to ionic bonding,typically found in inorganic
compounds,they are held togethervery rigidly and possess extremely high melting and boiling points.Inorganic
compounds are able to conduct electricity,s ince they contain metals (alkali, alkaline, transition,etc.).Othercharacteris tic
features ofinorganic compounds are thattheyare highly colored, andhave the ability to formcrystals.
Examples of some inorganic compounds:iron,coppersulfate,lead acetate,sodiumchloride,platinum,and so on.
#Define eachorganic and inorganic polymer structural formulas?
Polymers are linearly chained large molecules composed ofsequences ofrepeatingmonomerunits connectedby covalent
bonds.The polymers can be classified as organic and inorganic polymers....Inorganic polymers,with backbones typically
of silicon,phosphorous,oxygen,ornitrogen atoms,are intensively studied.
Formulas of Inorganic and Organic Compounds
Chemistry is the experimental and theoretical study of materials on their properties at both the macroscopic and
microscopic levels. Understanding the relationship between properties and structures/bonding is also a hot pursuit.
Chemistry is traditionally divided into organic andinorganic chemistry.The formeris the studyofcompounds containing
at least one carbon-hydrogen bonds.By default,the chemicalstudyofall othersubstances is called inorganic chemistry, a
less well defined subject.
However,the boundarybetween organic and inorganic compounds is not always well defined. For example, oxalic acid,
H2C2O4, is a compoundformed in plants,and it is generally considered an organic acid, but it does not contain any C-H
bond. Inorganic chemistry is also closely related to other disciplines such as materials sciences, physical chemistry,
thermodynamics, earth sciences, mineralogy, crystallography, spectroscopy etc.
A chemical formula is a format used to expressthe structure ofatoms.The formula tells which elements and how many of
each element are present in a compound.Formulas are written using the elementalsymbolofeach atomand a subscript to
denote the number of elements. This notation can be accredited to Swedish chemist Jons Jakob Berzeliu. The most
common elements presentin organic compounds are carbon,hydrogen,oxygen,and nitrogen.With carbon and hydrogen
present, other elements, such as phosphorous, sulfur, silicon, and the halogens, may exist in organic compounds.
Compounds that do not pertain to this rule are called inorganic compounds.
MolecularGeometry and StructuralFormula

Understanding howatoms in a molecule are arranged and how they are bonded together is very important in giving the
molecule its identity.Isomers are compoundsin which two molecules can have the same number of atoms, and thus the
same molecular formula, but can have completely different physical and chemical properties because of differences in
structural formula.
Polymers
A polymer is formed when small molecules of identicalstructure,monomers,combine into a large cluster. The monomers
are joined together by covalent bonds. When monomers repeat and bind, they form a polymer. While they can be
comprised ofnaturalorsynthetic molecules,polymers often includeplastics andrubber. When a molecule has more than
one ofthese polymers,square parenthesisare usedto show that all the elements within the polymer are multiplied by the
subscript outside ofthe parenthesis.The subscript (shown as n in the example below) denotes the number of monomers
present in the macromolecule (or polymer).
Molecular Formula
The molecular formula is based onthe actualmakeup ofthe compound.Althoughthe molecularformula can sometimes be
the same as the empirical formula, molecular compounds tendto be more helpful.However,they do not describe how the
atoms are put together. Molecular compounds are also misleading when dealing with isomers, which have the same
number and types of atoms (see above in molecular geometry and structural formula).
Methylpropane andbutane have the same molecularformula of C4H10, but are structurally different (methylpropane on the
left, butane on the right).
Ethylene becomes the polymer polyethylene.
Ex. Molecular Formula for Ethanol: C2H6O.
Empirical Formula
An empirical formula shows themost basic formof a compound. Empirical formulas show the number of atoms of each
element in a compound in the most simplified state using whole numbers. Empirical formulas tend to tell us very little
about a compound because one cannotdetermine the structure,shape,orproperties ofthe compoundwithout knowing the
molecular formula. Usefulness of the empirical formula is decreased because many chemical compounds can have the
same empirical formula.

Ex. Find the empirical formula for C8H16O2.
Answer: C4H8O (divide all subscripts by 2 to get the smallest, whole number ratio).
Structural Formula
A structuralformula displaysthe atoms of the molecule in the order they are bonded. It also depicts how the atoms are
bondedto one another,forexample single,double,and triple covalentbond. Covalent bonds are shown using lines. The
numberof dashes indicate whether the bond is a single, double, or triple covalent bond. Structural formulas are helpful
because theyexplain the propertiesand structure ofthe compoundwhich empiricaland molecular formulas cannot always
represent.
Ex. Structural Formula for Ethanol:
CondensedStructural Formula
Condensed structural formulas show the order of atoms like a structural formula but are written in a single line to save
space and make it more convenient andfasterto write out.Condensed structural formulas are also helpful when showing
that a group ofatoms is connectedto a single atomin a compound.When this happens, parenthesis are used around the
group of atoms to show they are together.
Ex. Condensed Structural Formula for Ethanol: CH3CH2OH (Molecular Formula for Ethanol C2H6O).
Line-AngleFormula
Because organic compoundscan be complexat times, line-angle formulas are used to write carbon and hydrogen atoms
more efficiently by replacing the letters with lines. A carbon atom is present wherever a line intersects another line.
Hydrogen atoms are then assumed to completeeach ofcarbon's fourbonds.Allotheratoms that are connected to carbon
atoms are written out. Line angle formulas help show structure and order of the atoms in a compound making the
advantages and disadvantages similar to structural formulas.
Ex. Line-Angle Formula for Ethanol:
Formulas of Inorganic Compounds
Inorganic compoundsare typically not ofbiologicalorigin.Inorganic compounds are made up of atoms connected using
ionic bonds. These inorganic compounds can be binary compounds, binary acids, or polyatomic ions.
Binary compounds
Binary compounds are formed between two elements, either a metal paired with a nonmetal or two nonmetals paired
together.Whena metal is paired with a nonmetal, they formionic compounds in which one is a negatively charged ion
and the otheris positvely charged. The net charge of the compound must then become neutral. Transition metals have
different charges; therefore,it is important to specify what type ofion it is during the naming ofthe compound.When two
nonmetals are paired together,the compound is a molecularcompound.Whenwriting out the formula, the element with a
positive oxidation state is placed first.

Ex. Ionic Compound: BaBr2(BariumBromide)
Ex. Molecular Compound: N2O4 (Dinitrogen Tetroxide)
Binary acids
Binary acids are binary compounds in which hydrogen bonds with a nonmetal forming an acid. However, there are
exceptions such as NH3, which is a base. This is because it shows no tendency to produce a H+
. Because hydrogen is
positively charged, it is placed first when writing out these binary acids.
Ex. HBr (Hydrobromic Acid)
Polyatomic ions
Polyatomic ions is formed when two or more atoms are connected with covalent bonds. Cations are ions that have are
postively charged,while anions are negatively charged ions. The most common polyatomic ions that exists are those of
anions.The two main polyatomic cationsare Ammoniumand Mercury (I). Many polyatomic ions are typically paired with
metals using ionic bonds to formchemical compounds.
Ex. MnO4
-
(Polyatomic ion); NaMnO4 (Chemical Compound)
Oxoacids
Many acids have three differentelements to formternary compounds. When one of those three elements is oxygen, the
acid is known as a oxoacid. In other words, oxacids are compounds that contain hydrogen, oxgygen, and one other
element.
Ex. HNO3 (Nitric Acid)
Complex Compounds
Certain compounds can appear in multiple forms yet mean the same thing. A common example is hydrates: water
molecules bond to anothercompound orelement.When this happens, a dot is shown between H2O and the other part of
the compound.Because the H2Omolecules are embeddedwithin the compound, the compound is not necessarily "wet".
When hydrates are heated, the water in the compound evaporates and the compound becomes anhydrous. These
compounds canbe used to attract watersuchas CoCl2.When CoCl2 is dry,CoCl2 is a blue colorwherease the hexahydrate
(written below) is pink in color.
Ex. CoCl2 2O
Formulas of Organic Compounds
Organic compounds contain a combinationcarbonandhydrogen or carbon and hydrogen with nitrogen and a few other
elements,such as phosphorous,sulfur,silicon,and the halogens.Mostorganic compounds are seenin biological origin, as
they are found in nature.
Hydrocarbons
Hydrocarbonsare compoundsthatconsist ofonly carbon and hydrogen atoms. Hydrocarbons that are bonded together
with only single bonds are alkanes. The simplest example is methane (shown below). When hydrocarbons have one or
more double bonds,theyare called alkenes.The simplest alkene is Ethane (C2H4) which contains a double bond between
the two carbon atoms.

Ex. Methane on left, Ethane on right
Functional Groups
Functional groups are atoms connected to carbon chains or rings of organic molecules. Compounds that are within a
functionalgrouptendto havesimiliar properties and characteristics. Two common functional groups are hydroxl groups
and carboxylgroups.Hydroxlgroups end in -OH and are alcohols. Carboxyl groups end in -COOH, making compounds
containing -COOHcarboxylic acids.Functional groups also help with nomenclature by using prefixes to help name the
compounds that have similar chemical properties.
Ex. Hydroxyl Group on top; Carboxyl Group on bottom
References
1. Miessler,Gary L. Inorganic Chemistry.2nd.UpperSaddle River:Prentince Hall, 1999.
2. Munowitz,Michael.Principles ofChemistry.Norton &Company:New York, 2000.
3. Pettrucci,Ralph H. General Chemistry:Principles and Modern Applications.9th.UpperSaddle River: Pearson
Prentice Hall, 2007.
Problems
1. Which ofthe following formulas are organic?
a. HClO
b. C5H10
c. CO2
2. What is the name ofthe following formula?

3. Classify the following formulas into theirappropriate functionalgroup
a. Acetic acid
b. Butanol
c. Oxalic acid
4. What are the empirical formulas for the following compounds?
a. C12H10O6
b. CH3CH2CH2CH2CH2CH2CH3
c. H3O
5. What is the name ofthe following figure and what is the molecularformula of the following figure?
Answer Key:
1. b and c. 2. Propane. 3. a. carboxyl group, b. hydrox, c. . 4. a. C6H5O3, b. C7H16, c. H3O. 5. Methylbutane, C5H12
## Distinguish between thermoplastic andthermosetting polymer?
The material difference betweenthe two is that.As a result of these physical qualities, thermoplastic materials have low
melting points while thermoset plastic products can withstand high temperatures without losing austerity.
Have you everwonderedwhat the difference between thermoplastic and thermosetting plastic is? Although both sound
similar, they have verydifferent propertiesandapplications.Belowwe discuss the differences betweenthermoplastics vs.
thermosetting plastic,theircuring process,and the pros andcons to each.Comprehending the performance differencescan
help you improve your product designs!
THERMOPLASTIC VS THERMOSETTING PLASTIC
Thermoplasticsand thermosetting plasticsare two separate classes ofpolymers,which are differentiatedbasedon their
behaviorin the presence ofheat. The materialdifference betweenthe two is that thermoplastics canbe remelted,
while thermoset plastics remainin a permanent solidstate once hardened. As a result ofthese physicalqualities,
thermoplastic materials have lowmelting points while thermoset plastic products canwithstand hightemperatures without
losing austerity.
THERMOPLASTICS CURING PROCESS
Thermoplastics pellets soften when heated and become more fluid as more heat is administered. The curing process is
100% reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and
recycled without negatively affecting the material’s physical properties. There are a variety of thermoplastic resins that
offer various performancebenefits,butthe majority ofmaterials commonly offer high strength,shrink-resistanceand easy

flexibility. Depending on the resin, thermoplastics can serve low-stress applications such as plastic bags or high-stress
mechanical parts. Examples of thermoplastic polymers include polyethylene, PVC, and nylon.
Thermoplastic Advantages:
 Highly recyclable
 High-Impact resistance
 Reshaping capabilities
 Chemical resistant
 Aesthetically superior finishes
 Hard crystalline or rubbery surface options
Thermoplastic Disadvantages:
 Expensive
 Can melt if heated
THERMOSET CURING PROCESS (THERMOSETTING PLASTIC)
RIM DefinitionThermoset plastics, typically processed by reaction injection molding, contain polymers that combine
together during the curing process to form a permanent chemical bond. This process forms weak bonds between the
monomer chains within these materials and eliminates the risk of the product remelting when heat is applied, making
thermosets ideal for high-heat applications like appliances and electronics. Thermoset plastics greatly improve the
material’s mechanical properties, providing enhanced chemical resistance, heat resistance and structural integrity.
Thermoset plastics are frequently used forsealed products due to theirresistanceto deformation andare also among some
of the most impact resistant plastics available. Examples of thermoset plastic polymers include epoxies, phenolics,
silicones, and polyesters.
Thermosetting Plastic Advantages:
 More resistant to high temperatures
 Highly flexible design
 Thick to thin wall capabilities
 High levels of dimensional stability
 Cost-effective
Thermosetting Plastics Disadvantages:
 Can’t be recycled
 More difficult to surface finish
 Can’t be remolded or reshaped

## What do you understand by copolymer?
Copolymerrefers to a kind ofpolymer that contains two ormore distinct repeating units called "monomers." It produces
high molecular weight substances by chemical combination or the polymerization of monomers. It is used to produce a
variety ofproducts like plastics,tires and tubes.Copolymer is different fromhomopolymer; homopolymer contains only
one kind of monomer, whereas copolymer contains at least two kinds of monomers. The properties of plastics can be
modified to meet specific needsthrough copolymerization.Copolymers are also used as corrosioninhibitors.They help to
improve the mechanical properties of plastic materials.
## Distinguish between homopolymer and copolymer?
Homopolymers are made up of same type of monomer units. And Copolymers are made up of more than one species of
monomer. the polymerization ofmonomers into copolymers is called copolymerization. Ifa polymer consists of only one
kind ofmonomers then it is called a homopolymer,while a polymerwhich consists ofmore than one kind of monomers is
called a copolymer.
## Discuss addition polymerization process?
Addition polymerization occurs by a chain reactionin which one carbon-carbondouble bond adds to another.Monomers
continue to react with the endofthe growing polymerchain in an addition polymerization reaction untilthe reactive
intermediate is destroyed in a termination reaction.Additionpolymerization is the successive addition of alkene
monomers to one another.The additionreactionmay occurby way ofradical,cationic,oranionic
intermediates.Condensationpolymerization is a reaction that joins two functionalgroups such as an alcoholand a
carboxylic acid and forms a secondsmallmolecule such as water.
Addition polymers are chain growth polymers because each intermediate adds another monomer unit one at a time.
Condensation polymers are step-growth polymers because condensation may occur between two smaller molecular
weight chains. Thus, the joining of oligomers results in a substantial increase in molecular weight in a single step.
## Discuss concentration polymerization process?
Polymerization Kinetics
The polymerization kinetics ofbenzoxazine resin and its copolymers,i.e.,benzoxazine (BA-a)/epoxy (EPON164) resins,
are discussedin this review.Nonisothermaldifferentialscanning calorimetry (DSC) at different heating rates is usedto
determine the kinetic parameters and the kinetic models proposedby Kissinger,Ozawa,Friedman, and Flynn-Wall-Ozawa
methods.BisphenolA-and aniline-based benzoxazine resin (BA-a)shows only one dominant autocatalytic polymerization
processwith the average activationenergy in a range of81-85 kJ/mol, whereas benzoxazine resin basedon BisphenolA
and 3,5-xylidine (BA-35×) exhibits two dominant polymerization processes signified by the clearsplit ofthe
polymerization exotherms.The average activation energies oflow-temperature polymerization (reaction (1))and high-
temperature curing (reaction(2)) were found to be 81-87 and 111-113 kJ/mol, respectively.Reaction(1)was found to be
autocatalytic in nature,while reaction (2)exhibited nth-orderpolymerization kinetics.Forthe BA-a/epoxy resin
(EPON164) copolymersystem,the copolymerexhibited two dominant polymerization processes.The reaction (1)at lower
temperature is attributedto the reaction amongthe BA-a,while the reaction (2) corresponds to the formation ofan
etherification betweenthe hydroxylgroup ofpoly(BA-a)and the epoxide group orthe homopolymerization reaction ofthe
epoxide group at high temperature.The averageactivationenergies ofreaction (1) and reaction (2)were determined to be

81 and 118 kJ/mol, respectively.The autocatalytic kinetic modelwas found to be the best description ofthe investigated
polymerization reactions.In addition,the predicted curves fromourkinetic models of BA-a, BA-35×, and BA-a/epoxy
resin (EPON164) fit well with the nonisothermalDSC thermograms.
Basic Kinetics ofFree-Radical Addition Polymerization
Polymerization kinetics is dealt with here only in sufficient depthto illustrate some points oftechnologicalsignificance.
This will involve certain simplifications andthe readerwishing to knowmore about this aspectofpolymerchemistry
should referto more comprehensive texts (e.g.,Flory,1953; Matyjaszewskiand Davis,2002; Young and Lovell,2011).
In a simple free-radical-initiated addition polymerization the principalreactions involved are (assuming termination by
combination forsimplicity):
where M, I, M , and I indicate monomers,initiators,and theirradicals,respectively,each initiatoryielding two
radicals.
The rate of initiation,Vi, that is,the rate of formation of growing polymerradicals,can be shownto be given by,
(2.13)Vi=2fkd[I]
where f is the fraction ofradicals which initiate chains,that is,the initiatorefficiency,and [I]is the initiator concentration.
The propagation rate is governed by the concentrations ofgrowing chains [M ]and ofmonomers [M].Since this is in
effect the rate of monomerconsumption,it also becomes the overallrate ofpolymerization.
(2.14)Rp=kp[M][M]
In mutualtermination the rate ofradical disappearance Vt is determined by the concentrationofgrowing radicals,and
since two radicals are involved in each termination the reaction is second order.
(2.15)Vt=2kt[M]2
In practice it is found that theconcentration ofradicals rapidly reaches a constantvalue andthe reaction takes place in the
steady state.Thus the rate ofradicalformation Vi becomes equalto the rate ofradicaldisappearanceVt.It is thus possible
to combine Eqns (2.13) and (2.15) to obtain an expression for[M ]in terms of the rate constants.
(2.16)[M]=(fkdkt[I])1/2
This equation indicatesthat the reaction rate is proportionalto the square root ofthe initiatorconcentrationand to the
monomer concentration.It is found thatthe relationship with initiatorconcentrationis commonly borne out in practice

(see Figure 2.5) but that deviationsmay occurwith respect to monomerconcentration.This may in some cases be
attributed to thedependencyof f on monomerconcentration,particularly at lowefficiencies,and to the effects ofcertain
solventsin solution polymerizations.
This may then be substituted into Eqn (2.14) to give:
(2.17)Rp=(fkdkt)1/2kp[M][I]
The most important technologicalconclusions fromthese kinetic studies may be summarised as follows:
(1) The formation of a polymer molecule takes place virtually instantaneously once an activecentre is formed.At any one
time the reacting systemwill contain monomerand complete polymerwith only a small amount ofgrowing radicals.
Increase ofreaction time will only increase the degree ofconversion(ofmonomerto polymer)and to first approximation
will not affect the degree ofpolymerisation.(In fact at high conversions thehigh viscosityofthe reacting mediummay
interfere with the ease oftermination so thatpolymers formed towards theend ofa reaction may have a somewhat higher
molecular weight.)
(2) An increase in initiatorconcentration orin temperature will increase the rate ofconversionbutdecrease molecular
weight.
(3)Transferreactions will reduce the degree ofpolymerisationwithout affectingthe rate ofconversion.
(4)The statisticalnature ofthe reaction leadsto a distributionofpolymermolecularweights.Figures quotedformolecular
weights are thus averagesofwhich different types exist.The numberaverage molecularweight takes into accountthe
numbers ofmolecules ofeach size when assessingthe average whereas the weightaverage molecularweight takesinto
account the fraction ofeach size by weight.Thus the presence of1% by weight ofmonomer would have little effect on the
weight average but since it had a great influence on the numberofmolecules presentperunit weight it would greatly
influence the numberaverage.The ratio ofthe two averages will provide a measure ofthe molecularweight distribution.
In the case ofemulsion polymerisation,halfthe micelles will be reacting at any one time.The conversion rate is thus
virtually independentofradicalconcentration (within limits) but dependenton the numberofmicelles (or swollen polymer
particles).
An increase in the rate ofradical production in emulsion polymerisationwill reduce the molecular weight since it will
increase the frequencyoftermination.An increase in the numberofparticles will, however,reduce the rate ofentry of

radicals into a specific micelle and increase molecularweight.Thus at constantinitiatorconcentration andtemperature an
increase in micelles (in effect in soap concentration)will lead to an increase in molecular weight and in rate of conversion.
The kinetics ofcopolymerisationare rathercomplexsince fourpropagation reactions cantake place iftwo monomers are
present.
## DiscussIonic polymerization process?
Ionic polymerization is a chain-growth polymerization in which active centers areions orion pairs.It can be considered
as an alternative to radicalpolymerization,and may refer to anionic polymerization orcationic polymerization.As
withradicalpolymerization,reactions are initiated by a reactive compound.
Applications
Because ofthe polarity of the active group on eachpolymerizing radical,termination by chain combinationis not seen in
ionic polymerization.Furthermore,because chargepropagationcan only occurby covalent bondformation with the
compatible monomerspecies,termination by chain transferordisproportionation is impossible.This means that all
polymerizing ions,unlike in radical polymerization,growand maintain theirchain lengths throughout the reaction
duration (so-called "living" polymerchains),untiltermination by the additionofa terminating molecule such as water.
This leads to virtually monodisperse polymerproducts,which have many applications in material analysis andproduct
design.Furthermore,becausethe ionsdo not self-terminate,blockcopolymers may be formed by the addition ofa new
monomer species.
A few important uses ofanionic polymerization includethe following:
 Calibration standardsfor gelpermeation chromatography
 Microphase separatingblockcopolymers
 Thermoplastic elastomeric materials
## DiscussRing opening polymerization process?
In polymerchemistry,ring-openingpolymerization(ROP)is a form of chain-growth polymerization,in which the terminus
of a polymerchain attacks cyclic monomers to forma longer polymer(see figure).The reactive centercan be radical,
anionic orcationic.
Monomers
Cyclic monomers that are amenable to ROP include epoxides,cyclic trisiloxanes,some lactones, lactides,cyclic
carbonates,and amino acid N-carboxyanhydrides.[4][5][6]
.[7]
Manystrained cycloalkenes,e.g norbornene,are suitable
monomers via ring-opening metathesis polymerization.
Mechanisms
Ring-opening polymerization can proceed via radical,anionic,orcationic polymerization as described
below.[13]
Additionally,radicalROP is usefulin producing polymers with functionalgroups incorporatedin the backbone
chain that cannot otherwise be synthesized via conventional chain-growth polymerization ofvinylmonomers.For
instance,radicalROPcan produce polymerswith ethers,esters,amides,and carbonates as functionalgroups alongthe
main chain.
Ring-opening metathesis polymerization
Ring-opening metathesis polymerization (ROMP)produces unsaturatedpolymers fromcycloalkenes orbicycloalkenes.It
requires organometallic catalysts.

The mechanismfor ROMP follows similar pathways as olefin metathesis.The initiation processinvolves thecoordination
of the cycloalkene monomerto the metalalkylidene complex, followed by a [2+2] type cycloadditionto formthe
metallacyclobutane intermediate thatcycloreverts to forma newalkylidene species.
Commercially relevant unsaturatedpolymers synthesized by ROMPinclude Norsorex(polynorbornene),Vestenamer
(polycyclooctene),and Metton(polycyclopentadiene).
Ahmad Shan –I- Ilahee Chowdhury
Department of Chemistry, M.Phill (Research),DUET

Advance polymer chemistry - Shan Chowdhury

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