2. • Macromolecules are collection of large number of unit molecules
linked together usually by a covalent bond.
• Many natural substances like proteins, rubber, diamond, chlorophyll
and hemoglobin etc. are the substance having large number of simple
molecules linked through covalent bond.
• Simple molecules usually called as monomer forms macromolecules
through the process of polymerization.
• Dimers are formed on combining two monomers, trimers on
combining three, tetramers on combining four and so on.
• In some cases, these repetitions are linear and hence chain is built
whereas in some cases these repetitions are branched and hence three
dimensional structure is build up.
Macromolecules
6. Polymer can have different chemical structures, physical properties,
mechanical behaviour, thermal characteristics etc. and can be classified in
different ways.
Natural and synthetic polymer.
Organic and inorganic polymer.
Thermoplastic and thermosetting polymers.
Classification Based on the structure of the polymers.
Addition and condensation polymers.
Homopolymers and copolymers.
Fibres, plastics and elastomers.
Linear branched and cross-linked polymers.
Classification of Polymers
7. Natural and synthetic polymer
i) Natural polymers are isolated from the natural materials.
Ex: Cotton, Silk, Wool, Natural Rubber, Proteins, Gums, etc.
ii) Synthetic polymers are derived from low molecular weight compound.
Ex: Ethylene to Polyethylene, Styrene to Polystyrene, etc.
Organic and inorganic polymer
i) Organic polymers generally made up of carbon atoms or hydrocarbons with
oxygen and nitrogen. Synthetic polymers are derived from organic polymers.
ii) Non-carbon polymers are referred to as Inorganic polymers. Glass and
silicon rubbers are the examples of inorganic polymers.
Classification of Polymers
8. Classification of Polymers
Thermoplastic and Thermosetting polymers
i) Certain polymers are heated and molded in a desired shape which can be
retained even after cooling. The process is usually repeated to heat, mold and
cool to desired shape. Polymer which gets soften on heating and stiff on
cooling are known as Thermoplastic polymers.
ii) There are certain polymers, that undergoes chemical transformation on
heating such as infusion like rice after cooking. Such polymers, that sets into
an infusible and insoluble mass after heating are called as Thermosetting
polymers.
Ex: Rice after cooking
9. Classification of Polymers
Plastics
Whenever, polymers are used for hard and tough utility articles by
application of heat and pressure, they are called as Plastics.
Examples: Polystyrene, PVC,, Polymethyl methacrylate, etc.
Elastomers
When polymers are designed and prepared for elastic nature application,
they are known as Elastomers.
Examples: Natural rubber, Silicon rubber, etc.
Fibers
When polymers are drawn for long length, usually more than 100 times its
diameter, they are called as fibers.
Example: Nylon and Terylene, etc.
Liquid Resins
Whenever, polymers are designed for sealants, adhesives or any other liquid
form application, which on drying become hard and strong are known as
Liquid Resins.
Example: Polymer paints, adhesives
10. Classification of Polymers
Polymers are further classified based upon how the monomer units are linked
together. Polymeric materials could be linear, branched, or cross-linked
subjected to the intermolecular linkages between the individual chains.
Linear, Branched and Cross-linked Polymers
11. Linear Polymers
•In linear polymers the repeating units are joined together end to end in a
single flexible chain.
•The polymeric chains are kept together through physical attractions.
These polymers have extensive Vander Waals attractions keeping the
chains together.
•Typically linear polymers are made from monomers with single end
group.
•Linear polymers containing side groups as part of monomer structure do
not qualify as branched polymers.
•Some of the common examples of linear polymers are polyethylene, PVC,
polystyrene, and polyamides.
•Linear polymers are generally more rigid.
12. Branched Polymers
• Branched polymers have side chains or branches growing out from the
main chain.
• The side chains or branches are made of the same repeating units as the
main polymer chains.
• The branches result from side reactions during polymerization.
• Monomers with two or more end groups are likely to support branching.
• For a polymer to classify as branched polymer the side chains or branches
should comprise of a minimum of one complete monomer unit.
• One of the most common example is low-density polyethylene (LDPE) and
has applications ranging from plastic bags, containers, textiles, and
electrical insulation, to coatings for packaging materials.
•The length of the side chains or branches differentiates between long- or
short-branched polymers.
13. Cross-linked Polymers
• Cross-linked polymers, as the name suggest, are polymers in which the
adjacent polymer chains are connected in a three-dimensional network
structure.
•The connections are also known as cross-links.
•The cross-links could be a consequence of covalent bonding between the
chains or branches.
•Cross-links tend to be permanent in nature.
•Once the cross-links between the chains develop the polymer then becomes
thermoset.
•Such polymers are characterized by their crosslink density or degree of
crosslink which is the indication of number of junction points per unit volume.
• Common examples include epoxies, bulk molding compounds, rubber, and
various adhesives.
14. Isotactic , Syndiotactic, Atactic in Polymers
What is Isotactic Polymer?
An isotactic polymer is a polymer which has the substituents on the same side
of the carbon chain. That means; all the substituents of the polymer material
are located on the same side of the backbone of the polymer.
The configuration in which all the ‘R’ groups lie on the same side of the plan
formed by the extended-chain backbone or all the asymmetric carbon atoms
have the same configuration i.e. either ‘d’ or ‘l’ are termed as Isotactic
polymers.
For example, industrially prepared polypropylene is isotactic. Its production
method is Ziegler-Natta catalysis. Usually, these polymers are semi-crystalline.
They show a helix configuration.
Isotactic
15. What is Syndiotactic Polymers
Syndiotactic polymers are polymer materials which have the substituents in
an alternating pattern. Therefore, substituent groups have alternate positions
along the backbone of the polymer.
The polymers in which asymmetric carbon atoms have alternate ‘d’ or ‘l’
configurations i.e. the substituent groups ‘R’ lies alternate above and below or
one and other side of the backbone chain are called as Syndiotactic polymers.
For examples, If we produce polystyrene via metallocene catalysis
polymerization, it gives a syndiotactic polystyrene material and it is a
crystalline material. The polymer contains 100% racemo diads (the diad
contains two units oriented in opposition).
Syndiotactic
16. An atactic polymer is a polymer material where the substituents in a
carbon chain are arranged in a random manner. Usually, polymers that form
via free radical polymerization has this structure; for example, polyvinyl
chloride. Atactic polymers have an amorphous structure due to the random
arrangement of substituent groups.
Polymers with no regular arrangements of ‘d’ or ‘l’ configurations of the
asymmetric carbon atoms or random arrangements of ‘R’ groups on either side
of backbone chain are known as Atactic Polymers.
Atactic
What is Atactic Polymers
20. Addition and Condensation Polymers
The process of combining a large number of small molecules to form a single
macromolecule is known as polymerization.
The small molecules that act as the building blocks of polymers are called
monomers.
Based on the kinds of reactions involved, polymerization is divided into two
groups known as addition polymerization and condensation polymerization.
Addition polymerization is the process of repeated addition of monomers that
possess double or triple bonds to form polymers.
Condensation polymerization is a process that involves repeated condensation
reactions between two different bi-functional or tri-functional monomers.
The main difference between addition and condensation polymerization is that in
addition polymerization the polymers are formed by the addition of monomers
with no by-products whereas in condensation polymerization, the polymers are
formed due to the condensation more than one different monomers resulting in the
formation of small molecules such as HCl, water, ammonia, etc., as by-products.
22. Addition Polymerization Condensation Polymerization
Monomers must have either a double
bond or triple bond
Monomers must have two similar or
different functional groups
Produces no by-products By-products such as ammonia, water
and HCl are produced
Addition of monomers results in
polymers
Condensation of monomers result in
polymers
The molecular weight of the resultant
polymers is a multiple of monomer’s
molecular weight
The molecular weight of the resultant
polymer is not a multiple of
monomer’s molecular weight
Lewis acids or bases, radical initiators
are catalysts in addition
polymerization
The catalysts in condensation
polymerization are catalysts in
condensation polymerization.
Common examples of addition
polymerization are PVC, polyethene,
Teflon etc.
Common examples of condensation
polymerization are nylon, bakelite,
silicon, etc.
Difference between
Addition and Condensation polymerization.
24. A polymers molecular weight is the sum of the atomic weights of the
individual atoms that comprise a molecule. It indicates
the average length of the bulk resin’s polymer chains.
One cannot surely guess about the exact degree of polymerization.
Under such condition, molecular weight of polymer can be viewed
statistically and expressed as some average of the molecular weights
contributed by the individual molecules that built the polymer.
The two most common and simple methods are
1) Number-average molecular weight or Number average molar mass
1) Mass average molecular weight or Weight average molar mass
Molar masses of polymers
25. Number-average molecular weight or Number average molar mass
The number average molecular weight is defined as the total weight
of polymer divided by the total number of molecules
The mass average molecular weight is defined as the sum of products
of molecular masses of groups of molecules with their respective
molecular masses and then sum is divided by the total mass.
Mass average molecular weight or Weight average molar mass
26. Determination of Molecular weight of polymers
Viscometry: The molecular weight obtained by this technique is the viscosity average
molecular weight, Mv.. The viscosity of a polymer solution is considerable high as
compared to that of pure solvent. The increase in viscosity by the macromolecules in a
solution is a direct function of the hydrodynamic volume and hence the molecular
weight of the macromolecules.
The relationship between viscosity of a polymer solution and molecular weight is
given by Mark-Houwink equation-
[η] = KMa
Where [η] is the intrinsic viscosity, M- molecular weight and a and K are constant for a
particular polymer/solvent/temperature system. Values of K and a are available for may
known polymers.
For a polymer type of known K and a values what is required is the determination of
the intrinsic viscosity using the above equation.
For unknown polymer systems, the K and a values are generated by fractionating the
polymer sample into several fractions and for each fraction the molecular weight is
determined by Osmometry or light scattering method and corresponding intrinsic
viscosity is measured.
Viscometry or Viscosity method
27. Determination of Molecular weight of polymers
Viscometry: A plot of log [η] against log M gives a straight line.
From the graph, the value of K and a can be determined from
their ordinate intercept and slope of the line.
[η] = KMa
log [η] = log K + a logM
Now, let us see how the intrinsic viscosity can be measures. Assume that a liquid is
flowing through a capillary tube. The time required for the liquid of volume V to pass
through the capillary of radius r and length l is related to its absolute viscosity by
the
Poiseuille Equation- η =
3.14 𝑃𝑟4𝑡
8 𝑉 𝑙
8𝑉𝑙η
t =
3.14𝑃𝑟4
Where P is the pressure head under which the liquid flow takes place.
If η and ηo are the absolute viscosities of a solution and the pure
solvent respectively and t and to are their corresponding time flow,
then
𝑡 η
η𝑟 =
𝑡
=
η
𝑜 𝑜
η/ ηo is known as the relative viscosity, ηr or ηrel
Viscometry or Viscosity method
28. Determination of Molecular weight of polymers
Commonly used terms in viscometry:
Intrinsic viscosity is also known as Staudinger index
or limiting viscosity index ( dimension is reciprocal of
concentration). For calculating the intrinsic viscosity
of a polymer sample in solution , we need not know
the absolute viscosities of solvent and solution, but
only the flow time of constant volume of solvent and
the solution through a particular tube. This principle
is used in the viscometric technique of molecular
weight determination. The term [η] has related to
the two viscosity functions through he following
twoequations by Huggins and Kraemer equations.
K” & k” are constants for a given
polymer solvent/ temperature system
Viscometry or Viscosity method
29. Determination of Molecular weight of polymers
Problem: Calculate the relative viscosity, specific viscosity, and reduced viscosity of a
0.5% (made by dissolving 0.25 g of polymer in 50 mL of solvent) solution where the
time for solvent flow between the two appropriate marks was 60 s and the time of
flow for the solution was 80 s.
Relative viscosity 𝜼𝒓 = 80 s/60 s = 1.3
The specific viscosity η𝑠𝑝 is determined by using the relation,
Specific viscosity, 𝜼𝒔𝒑 = 1.3-1 = 0.3
The reduced viscosity is ηred is given by the relation-
The most widely employed concentrations in viscosity determinations are g/mL (g/cc)
and g/dL or %. The units g/cc are recommended by IUPAC, while the units of % or g/dL
are the most commonly used units.
The reduced viscosity, ηred is-
𝑜
Solution: Using the relation of time of flow with relative viscosity, 𝑡 η
η𝑟 =
𝑡
=
η𝑜
η
𝑜
η𝑠𝑝 =
η
− 1
𝑟𝑒𝑑
η𝑠𝑝
η =
𝑐
Viscometry or Viscosity method
30. Determination of Molecular weight of polymers
Problem: Determine the molecular weight of a polystyrene sample which has an a value
of 0.60, a K value of 1.6 104 dL/g, and a limiting viscosity number or intrinsic viscosity of
0.04 dL/g.
Solution: The molecular weight can be found by the relationship:
Hence, the molecular weight of the polymer is 1 x 104
Viscometry or Viscosity method
31. Determination of Molecular weight of polymers
Osmometry or Osmotic pressureMethod
Osmometry: Membrane osmometry is absolute technique to determine Mn. The
solvent is separated from the polymer solution with semipermeable membrane that is
strongly held between the two chambers. One chamber is sealed by a valve with a
transducer attached to a thin stainless steel diaphragm which permits the
measurement of pressure in the chamber continuously. Membrane osmometry is
useful to determine Mn about 20,000-30,000 g/mol and less than 500,000 g/mol.
When Mn of polymer sample more than 500,000 g/mol, the osmotic pressure of
polymer solution becomes very small to measure absolute number average of
molecular weight. In this technique, there are problems with membrane leakage and
symmetry. The advantages of this technique is that it doesn’t require calibration and it
gives an absolute value of Mn for polymer samples.
Since osmotic pressure is dependent on colligative properties, i.e., the number of
particles present, the measurement of this pressure (osmometry) may be applied to
the determination of the osmotic pressure of solvents vs. polymer solutions.
32. Determination of Molecular weight of polymers
Osmotic pressure
The reciprocal of the number average molecular weight (Mn ) is the intercept when
data for π /RTC vs. C are extrapolated to zero concentration.
The difference in height (h) of the liquids in the columns may be
converted to osmotic pressure (π) by multiplying the gravity (g)
and the density of the solution (p), i.e., π = hpg.
In an automatic membrane osmometer, the unrestricted
capillary rise in a dilute solution is measured in
accordance with the modified van’t Hoff equation:
33. Determination of Molecular weight of polymers
Light Scattering Method: Light scattering methods to determination of weight average
molecular weight, Mw. When polarizable particles are placed in the oscillating electric
field of a beam of light, the light scattering occurs. Light scattering method depends on
the light, when the light is passing through polymer solution, it is measure by loses
energy because of absorption, conversion to heat and scattering. The intensity of
scattered light relies on the concentration, size and polarizability that is proportionality
constant which depends on the molecular weight.
Figure: Modes of scattering of light in solution. Figure: Schematic representation of light scattering.
For light scattering measurements, the total amount of the scattered light is deduced
from the decrease in intensity of the incident beam, I0, as it passes through a polymer
sample. This can be described in terms of Beer’s law for the absorption of light.
34. Determination of Molecular weight of polymers
Light scattering
The Beer’s law for the absorption of light as follows:
where is the measure of the decrease of the incident beam intensity
per unit length 1 of a given solution and is called the turbidity.
The intensity of scattered light or turbidity (τ) is proportional to the square of the
difference between the index of refraction (n) of the polymer solution and of the
solvent n0, to the molecular weight of the polymer (M), and to the inverse fourth power
of the wavelength of light used (λ). Thus,
where the expression for the constant H is
where n0 index of refraction of the solvent, n index of refraction of the solution, c concentration, the
virial constants B, C, etc., are related to the interaction of the solvent, P is the particle scattering
factor, and N is Avogadro’s number. The expression dn/dc is the specific refractive increment and is
determined by taking the slope of the refractive index readings as a function of polymer
concentration.
35. Determination of Molecular weight of polymers
Light scattering
In the determination of the weight-average molecular weight of polymer molecules in
dust-free solutions, one measures the intensity of scattered light from a mercury arc
lamp or laser at different concentrations and at different angles (θ), typically 0, 90, 45,
and 135. The incident light sends out a scattering envelope that has four equivalent
quadrants. The ratio of scattering at 45o compared with that for 135o is called the
dissymmetry factor or dissymmetry ratio Z. The reduced dissymmetry factor Z0 is the
intercept of the plot of Z as a function of concentration extrapolated to zero
concentration
Light-scattering envelopes. Distance from the scattering particle to the boundaries of
the envelope represents the magnitude of scattered light as a function of angle.
Scattering particle
Incident Light
Scattering particle
36. Determination of Molecular weight of polymers
Light scattering
Several expressions are generally used in describing the relationship between values
measured by light scattering photometry and molecular weight
At low concentrations of polymer in solution, the above equation reduces to an
equation of a straight line (y = b + mx):
When the ratio of the concentration c to the
turbidity (related to the intensity of scattering at 0
and 90) multiplied by the constant H is plotted
against concentration, the intercept of the
extrapolated curve, is the reciprocal of Mw and the
slope contains the virial constant B, as shown in
Figure. Typical plot used to determine
Mw-1 from light scattering data
37. Kinetics of Polymerization
The polymerization of alkenes occurs in a very different way than monomers that
undergo condensation reactions. Whether it occurs through an anionic, cationic, or
radical mechanism, polymerization of alkenes involves a chain reaction.
A typical radical polymerization starts with the thermal decomposition of a radical
initiator to provide two radicals. The rate of decomposition depends only on the
decomposition rate constant and the concentration of the initiator.
38. Once the radicals have been generated, they are able to undergo radical addition to
a monomer double bond. Although this is formally a radical propagation step, in
polymer chemistry it is termed the initiation step, because it is the first time a
monomer has undergone radical addition. This step consumes the first monomer
and produces a new radical species which will become the growing radical chain. It
requires a collision between the radical and a monomer, so the rate of initiation
depends on those two concentrations and the chain initiation rate constant, ki.
39. That rate law depends on a reactive intermediate. It's not a very helpful rate law,
because the reactive intermediate isn't something that we have directly measured out
and added to the reaction, and it might not even occur at high enough levels that we
can measure its concentration as the reaction progresses.
We usually look for ways to express the rate law in ways that do not include reactive
intermediates. In this particular situation, the way of getting around this situation is to
assume that the decomposition of the initiator is the rate determining step.
Making the radicals in the first place is probably the slow part because it is heavily
dependent on bond breaking, which is energy intensive. Once we have radical, it
probably undergoes addition to a monomer fairly quickly, initiating chain growth. If
that's true, we can assume that the chain initiation step proceeds very quickly
afterward, so that the rate really depends only on the rate of the decomposition step.
40. In practice, polymer chemists add another factor to the rate law. This factor, f, takes into
account the fact that only some of the radicals from the initiator actually react with
monomers to initiate growing chains. The rest decay through some other side reactions.
Usually, f is assumed to be around 0.5.
Once the first monomer has been initiated into a radical, it can react with another
monomer to enchain it and make a new radical. This is the principal propagation step of
the chain reaction. That step will keep repeating, adding more monomers into the
chain. The rate constant for this step, kprop or kp, is identical no matter how many
monomers have been enchained, but is distinct from ki because of the different nature
of the radical intermediates in the two different steps.
41. There is one last process, or group of processes, to complete the chain reaction cycle.
In termination, two radicals combine in some way to form closed-shell products.
There are a variety of ways that can happen in a radical polymerization. The simplest
event conceptually is coupling, in which two radical chains come together and form a
bond. That step is shown below.
42. Once again, these last two rates -- of propagation and of termination -- depend on
concentrations of reactive intermediates, which we do not typically know. This time
we will use a very standard assumption, which is that the concentration of this
reactive species remains constant, being consumed as soon as it is generated. The
usual way that we apply the steady state approximation is to assume zero change in
concentration of the reactive intermediate. That means that the sum of all the rates
for processes generating the intermediate equal the sum of all the rates consuming
the intermediate. In polymer chemistry, we take a slight shortcut, and just assume
that the rate of appearance of the radical in the first place equals its rate of
disappearance. We already have expressions for both of those rates.
By rearranging, we can get an expression for the
reactive chain end concentration. Then we can just
substitute the result into our expression for
propagation rate:
The result sums up the factors that control the growth
rate for the polymer. The growth rate increases linearly
with the concentration of monomer, and as the square
root of the initiator concentration. The rest of the
factors are just constants, so we can think of the rate
law as one combined constant and those two
concentration dependences.
43. Electronically conducting polymers
Electronically conducting polymers are macromolecules with greater electrical
and electronic conductivity.
Conducting polymers are conjugated polymers, namely organic compounds that
have an extended p-orbital system, through which electrons can move from one
end of the polymer to the other.
Like in metals or semiconductors, electronically conducting polymers also
resemble with the electrical conduction but with the help of conjugated
delocalized double bond.
The essential structural characteristic of all conductivity conjugated polymers is
their quasi-infinite π system extending over a large number of recurring monomer
units. This feature results in materials with directional conductivity. The extended
π system of conjugated polymer are highly susceptible to chemical or electrical
oxidation or reduction. These alter the electrical and optical properties of the
polymer, and by controlling this oxidation and reduction, it is possible to
systematically control the electrical and optical properties with a great deal of
precision.
45. Polyacetylene (IUPAC name: polyethyne) usually refers to an organic polymer with the
repeating unit (C2H2)n. The name refers to its conceptual construction
from polymerization of acetylene to give a chain with repeating olefin groups. This
compound is conceptually important, as the discovery of polyacetylene and its
high conductivity upon doping helped to launch the field of organic conductive
polymers.
Polyacetylene
Polyacetylene consists of a long chain of carbon atoms with alternating single
and double bonds between them, each with one hydrogen atom. The double bonds
can have either cis or trans geometry. The controlled synthesis of each isomer of the
polymer, cis-polyacetylene or trans-polyacetylene, can be achieved by changing the
temperature at which the reaction is conducted. The cis form of the polymer is
thermodynamically less stable than the trans isomer. Despite the conjugated nature of
the polyacetylene backbone, not all of the carbon–carbon bonds in the material are
equal: a distinct single/double alternation exists.Each hydrogen atom can be replaced
by a functional group. Substituted polyacetylenes tend to be more rigid than saturated
polymers. Furthermore, placing different functional groups as substituent's on the
polymer backbone leads to a twisted conformation of the polymer chain to interrupt
the conjugation.
46. Synthesis:
A variety of methods have been developed to synthesize polyacetylene, from
pure acetylene and other monomers. One of the most common methods
uses a Ziegler–Natta catalyst, such as Ti(OiPr)4/Al(C2H5)3, with gaseous
acetylene. This method allows control over the structure and properties of the
final polymer by varying temperature and catalyst loading. Mechanistic
studies suggest that this polymerization involves metal insertion into the triple
bond of the monomer.
Structure:
Polyacetylene is one of the most promising materials for applications in
optoelectronics.
47. Poly-sulphur nitride or Polythiazyl (SN)x
Polythiazyl (poly sulfur nitride), (SN)x, is an electrically conductive, gold- or bronze-
colored polymer with metallic luster. It was the first conductive inorganic
polymer discovered and was also found to be a superconductor at very low
temperatures (below 0.26 K). It is a fibrous solid, described as "lustrous golden on the
faces and dark blue-black", depending on the orientation of the sample. It is air stable
and insoluble in all solvents.
Structure and bonding:
The structure of the crystalline compound was resolved by X-ray diffraction. This
showed alternating SN bond lengths of 159 pm and 163 pm and SNS bond angles of 120
°C and NSN bond angles of 106 °C
48. Properties
Polythiazyl is a metallic-golden and shiny, crystalline but fibrous material.The polymer
is mostly inert to oxygen and water, but decomposes in air to a grey powder. At
temperatures above 240 °C explosive decomposition can occur. The compound also
explodes on impact.Polythiazyl shows an anisotropic electrical conductivity. Along the
fibres or SN chains, the bond is electrically conductive, perpendicular to it acts as an
insulator. The one-dimensional conductivity is based on the bonding conditions in the
S-N chain, where each sulfur atom provides two π electrons and each nitrogen atom
provides one π electron to form two-center 3π electron bonding units.
Synthesis
Polythiazyl is synthesized by the polymerization of the dimer disulfur dinitride (S2N2),
which is in turn synthesized from the cyclic alternating tetramer tetrasulfur
tetranitride (S4N4). Conversion from cyclic tetramer to dimer is catalysed with
hot silver wool.
i) S4N4 + 8 Ag → 4 Ag2S + 2 N2
ii) S4N4 (w/ Ag2S catalyst) → 2 S2N2 (w/ 77K cold finger) → S2N2
iii) S2N2 (@ 0°C, sublimes to surface) → thermal polymerization → (SN)x
Uses
Due to its electrical and electronical conductivity, polythiazyl is used
in LEDs, transistors, battery cathodes, and solar cells.
49. Poly-para-phenylene
PROPERTIES
Poly-para-phenylene (PPP), also called self-reinforced polyphenylene (SRP), is one
of the stiffest and strongest melt-processable engineering thermoplastics on the
market. Due to its inherent rigid rod-like structure, it possesses outstanding
mechanical properties over a wide temperature range including high strength and
modulus and moderate high impact strength. It also possesses a high glass
transition temperature (155°C) and a heat distortion temperature in the range of
150 - 160°C (300 - 325°F). Unlike most other high-performance thermoplasts, it has
excellent mechanical properties at very low temperatures without fiber
reinforcement. In addition, it possesses exceptional abrasion and solvent
resistance, outstanding thermal-oxidative stability, and inherent flame resistance.
Synthesis of
Poly-para-phynylene
50. Important performance properties of Poly-para-phenylene:
•Very high mechanical strength and stiffness
•High compression strength and high pressure resistance
•Excellent resistance to wear and scratching
•Good cold temperature properties (stable to about -270°C1)
•High glass transition temperature of about 155°C
•Outstanding dimensional stability before and after processing
•Low thermal expansion coefficient (low thermal shrinkage)
•Outstanding acid and base resistance
•Good solvent and hot steam resistance (but lower than PEEK1)
•Good processability (can be extruded and injection molded)
APPLICATIONS:
Its exceptional mechanical, chemical, thermal and electrical properties make SRP
an excellent choice for many very demanding applications including semiconductor
components, high performance bushings, bearings, valves, valve seats, and aircraft
substructures. Due to its high specific strength, SRP is an excellent candidate for
light-weight high-performance applications. Electrical conductive polyphenylene
(p- or n-doped) is used as an antistatic coating to protect integrated circuits from
static charges, humidity, and corrosion.
51. Poly-aniline
Polyaniline PANI is an intrinsically conductive polymer. The discovery of electrically
conductive polymer compositions based on polyaniline provides conductive materials,
which are soluble in selected organic solvents. These materials are which are melt
processable and exhibit good ambient stability characteristics.
Some polyaniline based materials are solution and melt processable. They offer clear
benefits over traditional plastics made conductive by the addition of fillers (carbon
blacks, metal particles and flakes, metal fibres, carbon fibres, and others). They provide
precisely controlled electrical conductivity over a wide range, improve phase
compatibility and thus blendability with bulk polymers, provide easier means of
processing and forming conductive products and provide low cost solutions for the
production of transparent and coloured thin films and coatings.
Synthesis of Polyaniline
52. Properties and advantages of Polyaniline
The electrical conductivity of polyaniline based compositions can be closely
controlled over a wide range.
Polyaniline based compositions can be processed using conventional techniques
such as blow and injection moulding, extrusion, calendering, film casting, and
fibre spinning.
Electrically conductive polyaniline based blends with commodity polymers can
be produced by using common solution and melt processing techniques.
Plasticised polyaniline compositions improve melt processing performance by
lowering the melt-viscosity, lowering the processing temperature and shortening
the processing time.
Electrically conductive, coloured and transparent thin films and coatings, which
would otherwise be difficult to achieve with conventional filled materials, can be
made using polyaniline based compositions.
53. Applications of Poly-aniline
• Neat materials, blends, compounds and solutions
Polyaniline based conductive polymers can be used neat, or as blends and
compounds with commodity polymers.
• Electrostatic discharge (ESD) protection materials
One target application of these materials is the protection from electrostatic
discharge (ESD).
• In terms of yarn and fiber, Polyaniline PANI can be applied for conductive textiles,
antistatic floors, automotive industry, etc.
