1 general polymer science

 Introduction to polymers
 Classification of polymers
 Structures & properties of polymers
 Biodegradable polymers
 General mechanism of drug release
 Application in conventional dosage forms
 Applications in controlled drug delivery
 References
7th Sept. 2010 KLECOP, Nipani
1

 A polymer is a very large molecule in which one
or two small units is repeated over and over
again
 The small repeating units are known as
monomers
 Imagine that a monomer can be represented by
the letter A. Then a polymer made of that
monomer would have the structure:
-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-
A-A-A-A-A-A-A
2

In another kind of polymer, two different monomers
might be involved
If the letters A and B represent those monomers, then
the polymer could be represented as:
-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-
B-A-B-A
A polymer with two different monomers is known as
a copolymer.
3

 Polymers are organic, chain molecules
 They can, vary from a few hundreds to thousands
of atoms long.
 There are three classes of polymers that we will
consider:-
a. Thermo-plastic - Flexible linear chains
b. Thermosetting - Rigid 3-D network
c. Elastomeric - Linear cross-linked chains
4

 In simple thermoplastic polymers, the chains are
bound to each other by weaker Van der Waal’s forces
and mechanical entanglement.
 Therefore, the chains are relatively strong, but it is
relatively easy to slide and rotate the chains over each
other.
5

 Common elastomers are made from highly coiled,
linear polymer chains.
 In their natural condition, elastomers behave in a
similar manner to thermoplastics (viscoelastic)
– i.e. applying a force causes the chains to uncoil and
stretch, but they also slide past each other causing
permanent deformation.
 This can be prevented by cross-linking the polymer
chains
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6

 Polymers can be represented by
 – 3-D solid models
 – 3-D space models
 – 2-D models
7

 The mechanical properties are also governed by the
structure of the polymer chains.
 They can be:
Linear Network (3D)
Branched
Cross-linked
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8

 Before we discuss how the polymer chain molecules
are formed, we need to cover some definitions:
 The ethylene monomer looks like
 The polyethylene molecule looks like:
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9

 Polyethylene is built up from repeat units or mers.
 Ethylene has an unsaturated bond. (the double bond
can be broken to form two single bonds)
 The functionality of a repeat unit is the number of sites
at which new molecules can be attached.
10

 When polymers are fabricated, there will always be a
distribution of chain lengths.
 The properties of polymers depend heavily on the
molecule length.
 There are two ways to calculate the average molecular
weight:
1 Number Average Molecular Weight
2. Weight Average Molecular Weight
11

 Number Average Molecular Weight
Mn= Σ Xi Mi
Where, xi = number of chains in the ith weight range
Mi = the middle of the ith weight range
 Weight Average Molecular Weight
Mw = Σ Wi Mi
Where, wi = weight fraction of chains in the ith range
Mi = the middle of the ith weight range
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12

 The mechanical properties of a polymer are dictated in
part by the shape of the chain.
 Although we often represent polymer chains as being
straight,
 They rarely are.
13

 The carbon – carbon bonds in simple polymers form
angles of 109º
7th Sept. 2010
Contd…
14

 Thermoplastic polymers go through a series of
changes with changes in temperature. (Similar to
ceramic glasses)
 In their solid form they can be semi-crystalline or
amorphous (glassy).
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 The ability of a polymer to crystallize is affected by:
1. Complexity of the chain: Crystallization is easiest for
simple polymers (e.g. polyethylene) and harder for
complex polymers (e.g. with large side groups, branches,
etc.)
2. Cooling rate: Slow cooling allows more time for the
chains to align
3. Annealing: Heating to just below the melting
temperature can allow chains to align and form crystals
4. Degree of Polymerization: It is harder to crystallize
longer chains
5. Deformation: Slow deformation between Tg and Tm can
straighten the chains allowing them to get closer
together.
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CLASSIFICATION POLYMERS:
 ON BASIS OF INTERACTION WITH WATER:
 Non-biodegradable hydrophobic Polymers
E.g. polyvinyl chloride, polyethylene vinyl acetate
 Soluble Polymers E.g. HPMC, PEG
 Hydrogels E.g. Polyvinyl pyrrolidine
 BASED ON POLYMERISATION METHOD:
 Addition Polymers E.g. Alkane Polymers
 Condensation polymers E.g. Polysterene and Polyamide
 Rearrangement polymers
 BASED ON POLYMERIZATION MECHANISM:
 Chain Polymerization
 Step growth Polymerization
19

 BASED ON CHEMICAL STRUCTURE:
 Activated C-C Polymer
 Polyamides, polyurethanes
 Polyesters, polycarbonates
 Polyacetals, Polyketals, Polyorthoesters
 Inorganic polymers
 Natural polymers
 BASED ON OCCURRENCE:
 Natural polymers E.g. 1. Proteins-collagen, keratin,
albumin, 2. carbohydrates- starch, cellulose
 Synthetic polymers E.g. Polyesters, polyamides
Contd….
20

 BASED ON BIO-STABILITY:
 Bio-degradable
 Non Bio-degradable
Contd….
21

 Should be versatile and possess a wide range of
mechanical, physical, chemical properties
 Should be non-toxic and have good mechanical strength
and should be easily administered
 Should be inexpensive
 Should be easy to fabricate
 Should be inert to host tissue and compatible with
environment
22

 The polymer should be soluble and easy to synthesis
 It should have finite molecular weight
 It should be compatible with biological environment
 It should be biodegradable
 It should provide good drug polymer linkage
23

 There are three primary mechanisms by which active
agents can be released from a delivery system: namely,
 Diffusion, degradation, and swelling followed by
diffusion
 Any or all of these mechanisms may occur in a given
release system
 Diffusion occurs when a drug or other active agent
passes through the polymer that forms the controlled-
release device. The diffusion can occur on a
macroscopic scale as through pores in the polymer
matrix or on a molecular level, by passing between
polymer chains
GENERAL MECHANISM OF DRUG RELEASE FROM
POLYMER
24

Drug release from typical matrix
release system
25

 For the reservoir systems the drug delivery rate can remain
fairly constant.
 In this design, a reservoir whether solid drug, dilute
solution, or highly concentrated drug solution within a
polymer matrix is surrounded by a film or membrane of a
rate-controlling material.
 The only structure effectively limiting the release of the
drug is the polymer layer surrounding the reservoir.
 This polymer coating is uniform and of a nonchanging
thickness, the diffusion rate of the active agent can be kept
fairly stable throughout the lifetime of the delivery system.
The system shown in Figure a is representative of an
implantable or oral reservoir delivery system, whereas the
system shown in b.
26


27


28

 It is also possible for a drug delivery system to be
designed so that it is incapable of releasing its agent or
agents until it is placed in an appropriate biological
environment.
 Controlled release systems are initially dry and, when
placed in the body, will absorb water or other body
fluids and swell,
 The swelling increases the aqueous solvent content
within the formulation as well as the polymer mesh
size, enabling the drug to diffuse through the swollen
network into the external environment.
29

 Examples of these types of devices are shown in
Figures a and b for reservoir and matrix systems.
 Most of the materials used in swelling-controlled
release systems are based on hydrogels, which are
polymers that will swell without dissolving when
placed in water or other biological fluids. These
hydrogels can absorb a great deal of fluid and, at
equilibrium, typically comprise 60–90% fluid and only
10–30% polymer.
30


Drug delivery from (a) reservoir
and (b) matrix swelling-controlled
release systems.
31

Stimulus Hydrogel Mechanism
pH Acidic or basic
hydrogel
Change in pH-
swelling- release of
drug
Ionic strength Ionic hydrogel Change in ionic
strength change in
concentration of ions
inside gel change in
swelling release of
drug
Chemical species Hydrogel
containing
electron-accepting
groups
Electron-donating
compounds formation
of charge/transfer
complex change in
swelling release of
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32

Enzyme-
substrate
Hydrogel
containing
immobilized
enzymes
Substrate present
enzymatic conversion
product changes swelling
of gel release of drug
Magnetic Magnetic particles
dispersed in
alginate
microshperes
Applied magnetic field
change in pores in gel
change in swelling release
of drug
Thermal Thermoresponsive
hrydrogel poly(N-
isopro-
pylacrylamide
Change in temperature
change in polymer-polymer
and water-polymer
interactions change in
swelling release of drug
33

 The pharmaceutical applications of polymers range
from their use as binders in tablets
 Viscosity and flow controlling agents in liquids,
suspensions and emulsions
 Polymers are also used as film coatings to disguise
the unpleasant taste of a drug, to enhance drug
stability and to modify drug release characteristics.
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 Tablets :
- As binders
- To mask unpleasant taste
- For enteric coated tablets
 Liquids :
- Viscosity enhancers
- For controlling the flow
 Semisolids :
- In the gel preparation
- In ointments
 In transdermal Patches
35

 Reservoir Systems
- Ocusert System
- Progestasert System
- Reservoir Designed Transdermal Patches
 Matrix Systems
 Swelling Controlled Release Systems
 Biodegradable Systems
 Osmotically controlled Drug Delivery
36

BIO DEGARADABLE POLYMERS
37

 Biodegradable polymers can be classified in two:
 Natural biodegradable polymer
 Synthetic biodegradable polymer
 Synthetic biodegradable polymer are preferred more than
the natural biodegradable polymer because they are free of
immunogenicity & their physicochemical properties are
more predictable &reproducible
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 PHYSICAL FACTORS
 Shape & size
 Variation of diffusion coefficient
 Mechanical stresses
 CHEMICAL FACTORS
 Chemical structure & composition
 Presence of ionic group
 Distribution of repeat units in multimers
 configuration structure
 Molecular weight
 Morphology
 Presence of low molecular weight compounds
39

 Processing condition
 Annealing
 Site of implantation
 Sterilization process
 PHYSICOCHEMICAL FACTORS
 Ion exchange
 Ionic strength
 pH
CONTD
40

 Localized delivery of drug
 Sustained delivery of drug
 Stabilization of drug
 Decrease in dosing frequency
 Reduce side effects
 Improved patient compliance
 Controllable degradation rate
41

The polymer can protect the drug from the physiological
environment & hence improve its stability in vivo.
Most biodegradable polymer are designed to degrade within the
body as a result of hydrolysis of polymer chain into biologically
acceptable & progressively small compounds.
TYPES OF POLYMER DRUG DELIVERY SYSTEM:
MICRO PARTICLES: These have been used to deliver
therapeutic agents like doxycycline.
NANO PARTICLES: delivery drugs like doxorubicin,
cyclosporine, paclitaxel, 5- fluorouracil etc
42

 POLYMERIC MICELLES: used to deliver therapeutic agents.
 HYDRO GELS: these are currently studies as controlled
release carriers of proteins & peptides.
 POLYMER MORPHOLOGY:
The polymer matrix can be formulated as either
micro/nano-spheres, gel, film or an extruded shape.
The shape of polymer can be important in drug release
kinetics.
43

 For specific site drug delivery- anti tumour agent
 Polymer system for gene therapy
 Bio degradable polymer for ocular, non- viral DNA,
tissue engineering, vascular, orthopaedic, skin adhesive
& surgical glues.
 Bio degradable drug system for therapeutic agents such
as anti tumor, antipsychotic agent, anti-inflammatory
agent and biomacro molecules such as proteins,
peptides and nucleic acids
44

 Polymers play an vital role in both conventional as well as
novel drug delivery. Among them , the use of bio
degradable polymer has been success fully carried out.
 Early studies on the use of biodegradable suture
demonstrated that these polymers were non- toxic &
biodegradable.
 By incorporating drug into biodegradable polymer whether
natural or synthetic, dosage forms that release the drug in
predesigned manner over prolong time
45

 The release of drugs from the erodible polymers occurs
basically by three mechanisms,
I. The drug is attached to the polymeric backbone by a
labile bond, this bond has a higher reactivity toward
hydrolysis than the polymer reactivity to break down.
II. The drug is in the core surrounded by a biodegradable
rate controlling membrane. This is a reservoir type device
that provides erodibility to eliminate surgical removal of
the drug-depleted device.
III. a homogeneously dispersed drug in the biodegradable
polymer. The drug is released by erosion, diffusion, or a
combination of both.
46

Schematic representation of drug release mechanisms In mechanism 1, drug is released by
hydrolysis of polymeric bond. In mechanism 2, drug release is controlled by biodegradable
membrane. In mechanism 3, drug is released by erosion, diffusion, or a combination of both
47

 The term 'biodegradation' is limited to the description of
chemical processes (chemical changes that alter either the
molecular weight or solubility of the polymer)
 ‘Bioerosion' may be restricted to refer to physical
processes that result in weight loss of a polymer device.
 The erosion of polymers basically takes place by two
methods:-
1. Chemical erosion
2. Physical erosion
48

 There are three general chemical mechanisms that cause
bioerosion
1. The degradation of water-soluble macromolecules that are
crosslinked to form three-dimensional network.
As long as crosslinks remain intact, the network is intact
and is insoluble.
Degradation in these systems can occur either at crosslinks
to form soluble backbone polymeric chains (type IA) or at
the main chain to form water-soluble fragments (type IB).
Generally, degradation of type IA polymers provide high
molecular weight, water-soluble fragments, while
degradation of type IB polymers provide low molecular
weight, water soluble oligomers and monomers
49

50

2. The dissolution of water-insoluble macromolecules with
side groups that are converted to water-soluble polymers
as a result of ionization, protonation or hydrolysis of the
groups. With this mechanism the polymer does not
degrade and its molecular weight remains essentially
unchanged. E.g. cellulose acetate
3. The degradation of insoluble polymers with labile bonds.
Hydrolysis of labile bonds causes scission of the polymer
backbone, thereby forming low molecular weight, water-
soluble molecules. E.g. poly (lactic acid), poly (glycolic
acid)
The three mechanisms described are not mutually exclusive;
combinations of them can occur.
51

 The physical erosion mechanisms can be
characterized as heterogeneous or homogeneous.
 In heterogeneous erosion, also called as surface
erosion, the polymer erodes only at the surface,
and maintains its physical integrity as it degrades.
As a result drug kinetics are predictable, and zero
order release kinetics can be obtained by applying
the appropriate geometry. Crystalline regions
exclude water. Therefore highly crystalline
polymers tend to undergo heterogeneous erosion.
E.g polyanhydrides
52

 Homogeneous erosion, means the hydrolysis
occurs at even rate throughout the polymeric
matrix. Generally these polymers tend to be
more hydrophilic than those exhibiting surface
erosion. As a result, water penetrates the
polymeric matrix and increases the rate of
diffusion. In homogeneous erosion, there is
loss of integrity of the polymer matrix. E.g
poly lactic acid
53

 Natural polymers
 Polymers are very common in nature
 some of the most widespread naturally occurring substances are
polymers Starch and cellulose are examples
 Green plants have the ability to take the simple sugar known as
glucose and make very long chains containing many glucose units
These long chains are molecules of starch or cellulose
If we assign the symbol G to stand for a glucose molecule, then starch
or cellulose can be represented as:
 -G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-G-
54

 Natural polymers remains the primary choice of
formulator because
- They are natural products of living organism
- Readily available
- Relatively inexpensive
- Capable of chemical modification
 Moreover, it satisfies most of the ideal requirements of
polymers.
 But the only and major difficulty is the batch- to-batch
reproducibility and purity of the sample.
55

 Examples :
1) Proteins :
- Collagen : Found from animal tissue.
Used in absorbable sutures, sponge
wound dressing, as drug delivery vehicles
- Albumin : Obtained by fabrication of
blood from healthy donor.
Used as carriers in nanocapsules &
microspheres
- Gelatin : A natural water soluble polymer
Used in capsule shells and also as coating
material in microencapsulation.
56

2) Polysaccharides :
- Starch : Usually derivatised by introducing acrylic
groups before manufactured int microspheres.
Also used as binders.
- Cellulose :
Naturally occuring linear polysaccharide. It
is insoluble in water but solubility can be obtained by
substituting -OH group.
Na-CMC is used as thickner, suspending agent, and
film formers.
3) DNA & RNA :
They are the structural unit of our body.
DNA is the blueprint that determines everything
of our body.
57

 Diffusion controlled systems
 Solvent activated systems
 Chemically controlled systems
 Magnetically controlled systems
58

 Reservoir type
 Shape : spherical, cylindrical, disk-like
 Core : powdered or liquid forms
 Properties of the drug and the polymer : diffusion
rate and release rate into the bloodstream
 Problems : removal of the system, accidental rupture
 Matrix type
 Uniform distribution and uniform release rate
 No danger of drug dumping
59

 Osmotically controlled system
 Semipermeable membrane
 Osmotic pressure decrease concentration gradient
 Inward movement of fluid : out of the device
through a small orifice
 Swelling controlled system
 Hydrophilic macromolecules cross-linked to form a
three-dimensional network
 Permeability for solute at a controlled rate as the
polymer swells
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60

 Pendant-chain system
 Drug : chemically linked to the backbone
 Chemical hydrolysis or enzymatic cleavage
 Linked directly or via a spacer group
 Bioerodable or biodegradable system
 Drug : uniformly dispersed
 Slow released as the polymer disintegrates
 No removal from the body
 Irrespective of solubility of drug in water
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61

 Cancer chemotherapy
 Selective targeting of antitumor agents
 Minimizing toxicity
 Magnetically responsive drug carrier systems
 Albumin and magnetic microspheres
 High efficiency for in vivo targeting
 Controllable release of drug at the microvascular
level
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62

 Medisorb
• Microencapsulation by PLA, PGA, PLGA
• Drug release : week to one year
 Alzamer
• Bioerodible polymer : release at a controlled rate
• Chronic disease, contraception, topical therapy
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63

 Poly(L-lactic acid) for release of progesterone, estradiol,
dexamethasone
 Copolymer of gluconic acid and –ethyl-L-glutamte as bioerodible
monolithic device
 PLA, PGA, PLGA for parenteral administration of polypeptide
 Sustained release (weeks or months)
Orahesive® : sodium carboxymethyl cellulose, Pectin,
gelatin
 Orabase ® : blend in a polymethylene/mineral oil base
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 Novel drug delivery systems – Y.W.Chien –
Dekker 50
 Bio–adhesive drug delivery system –
Dekker 98
 Encyclopedia of controlled drug delivery
systems.
 www.google.com
7th Sept. 2010
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Spherulite, rubber specimen. Chain-folded lamellar crystallites, ~10 nm thick, 30,000×

69
ISSUES TO ADDRESS...
• What are the general structural and chemical
characteristics of polymer molecules?
• What are some of the common polymeric
materials, and how do they differ chemically?
• How is the crystalline state in polymers different
from that in metals and ceramics ?

Structures of Polymers
• Introduction and Motivation
– Polymers are extremely important materials (i.e. plastics)
– Have been known since ancient times – cellulose, wood, rubber,
etc..
– Biopolymers – proteins, enzymes, DNA …
– Last ~50 years – tremendous advances in synthetic polymers
– Just like for metals and ceramics, the properties of polymers
• Thermal stability
• Mechanical properties
Are intimately related to their molecular structure …

Originally natural
polymers were used:
 Wood
 Rubber
 Cotton
 Wool
 Leather
 Silk
71
Oldest known use:
Rubber balls used by Incas
Noah used pitch (a natural polymer) for the ark
Noah's pitch
Genesis 6:14 "...and cover it inside
and outside with pitch."
gum based resins
extracted from
pine trees

Most polymers are hydrocarbons
– i.e., made up of H and C
 Saturated hydrocarbons
 Each carbon singly bonded to four other atoms
 Example:
 Ethane, C2H6
72
C C
H
H H
H
H
H

 Double & triple bonds somewhat unstable
 Thus, can form new bonds
 Double bond found in ethylene or ethene - C2H4
 Triple bond found in acetylene or ethyne - C2H2
73
C C
H
H
H
H
C C HH

 about hydrocarbons
 Why? Most polymers are hydrocarbon (e.g. C, H) based
 Bonding is highly covalent in hydrocarbons
 Carbon has four electrons that can participate in bonding,
hydrogen has only one
 Saturated versus unsaturated
C C
C C
H
H
H
H
H H
Ethylene
Acetylene
C C
H
H
H
H
H
H
Ethane
Unsaturated Saturated
• Unsaturated – species contain
carbon-carbon double/triple
bonds
• Possible to substitute
another atom on the carbon
• Saturated – carbons have four
atoms attached
• Cannot substitute another
atom on the carbon

c04eqf02
Hydrocarbon Molecules
Ethylene
Ethene
Acetylene
Ethyne
(normal) butane
isobutane
Hydrocarbons have strong chemical bonds, but
interact only weakly with one another (van der
Waals’ forces)

compounds with same chemical formula can have
quite different structures
for example: C8H18
 normal-octane
C C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=
H3C CH
CH3
CH2 CH
CH2
CH3
CH3
H3C CH2 CH3( )
6

Isomerism – compounds of the
same chemical composition but
different atomic arrangements (i.e.
bonding connectivity)
2,4-dimethylhexane

Polymer Molecules
Molecules are gigantic
Macromolecules
Repeat units
Monomer

4.3 Polymers
• Polymer molecules
– what is a polymer?
– Polymers are molecules (often called
macromolecules) formed from a series of building
units (monomers) that repeat over and over again
*
C
C
H H
poly-ethylene
*
H H
mer unit :
C
C
H H
H H
n
n is often a very large number!
e.g. can make polyethylene with MW > 100,000! ~3600 mers ~7200 carbons
• polymers can have a range of
molecular weights
• There are many monomers
• Can make polymers with
different monomers, etc..

Chemistry of polymer molecules
Example: ethylene
• Gas at STP
• To polymerize ethylene, typically increase T, P and/or add an initiator
C C
H
H
H
H
+ R C C
H
H
H
H
R
C C
H
H
H
H
R + C C
H
H
H
H
C C
H
H
H
H
R C C
H
H
H
H
R* = initiator; activates the monomer to begin chain growth
After many additions of monomer to the growing chain…
*
C
C
H H
poly-ethylene
*
H H
n
Initiation
Propagation
C
H
H
O O C
H
H
C
H
H
O2 R= 2
Initiator: example - benzoyl peroxide

4.4 Polymer chemistry
• Polymers are chain molecules. They are built
up from simple units called monomers.
• E.g. polyethylene is built from ethylene units:
which are assembled into long chains:
Polyethylene or polythene (IUPAC name poly(ethene)) is a
thermoplastic commodity heavily used in consumer products
(notably the plastic shopping bag). Over 60 million tons of the
material are produced worldwide every year.

c04eqf08
c04eqf09
Tetrafluoroethylene monomer polymerize to form PTFE or
polytetrafluoroethylene
Vinyl chloride monomer leads to poly(vinyl chloride) or PVC
poly(tetrafluoroethene) or poly(tetrafluoroethylene) (PTFE) is a synthetic
fluoropolymer. PTFE is the DuPont brand name Teflon. Melting: 327C
PVC: manufacturing toys,
packaging, coating, parts in motor
vehicles, office supplies,
insulation, adhesive tapes,
furniture, etc. Consumers: shoe
soles, children's toys, handbags,
luggage, seat coverings, etc.
Industrial sectors: conveyor belts,
printing rollers. Electric and
electronic equipment: circuit
boards, cables, electrical boxes,
computer housing.

84
Adapted from Fig.
4.1, Callister &
Rethwisch 3e.
Note: polyethylene is a long-chain hydrocarbon
- paraffin wax for candles is short polyethylene
• Polymer = many mers
Adapted from Fig. 14.2, Callister 6e.

Polymer chemistry
– In polyethylene (PE) synthesis, the monomer is ethylene
– Turns out one can use many different monomers
• Different functional groups/chemical composition – polymers have very
different properties!
*
C
C
H H
poly(ethylene)
(PE)
*
H H
n *
C
C
F F
poly(tetrafluoroethylene)
(PTFE, teflon)
*
F F
n
*
C
C
H H
poly(vinylchloride)
(PVC)
*
Cl H
n *
C
C
H H
poly(styrene)
(PS)
*
H
n
Monomers
C C
H
H
H
H
C C
F
F
F
F
C C
H
H
H
Cl
C C
H
H
H

Homopolymer and Copolymer
• Polymer chemistry
– If formed from one monomer (all the repeat units are
the same type) – this is called a homopolymer
– If formed from multiple types of monomers (all the
repeat units are not the same type) – this is called a
copolymer
• Also note – the monomers shown before are
referred to as bifunctional
– Why? The reactive bond that leads to polymerization
(the C=C double bond in ethylene) can react with two
other units
– Other monomers react with more than two other units
– e.g. trifunctional monomers

88
Molecular weight, M: Mass of a mole of chains.
low M
high M
Not all chains in a polymer are of the same length
i.e., there is a distribution of molecular weights

 The properties of a polymer depend on its length
 synthesis yields polymer distribution of lengths
 Define “average” molecular weight
 Two approaches are typically taken
 Number average molecular weight (Mn)
 Weight-average molecular weight (Mw)

90
xi = number fraction of chains in size range i
moleculesof#total
polymerofwttotal
nM
iiw
iin
MwM
MxM


Adapted from Fig. 4.4, Callister & Rethwisch 3e.
wi = weight fraction of chains in size range i
Mi = mean (middle) molecular weight of size range i

Molecular weight
Are the two different? Yes, one is essentially based
on mole fractions, and the other on weight fractions
They will be the same if all the chains are exactly of the
same MW! If not Mw > Mn
Get Mn
from this
Get Mw from
this

Molecular weight
– Other ways to define polymer MW
– Degree of polymerization
• Represents the average number of mers in
a chain. The number and weight average
degrees of polymerization are
m
M
n
n
n 
m
M
n
w
w 
m is the mer MW in both cases. In the case of a
copolymer (something with two or more mer units), m
is determined by  jjmfm
fj and mj are the chain fraction and molecular
weight of mer j

Example Problem 4.1
– Given the following data determine the
• Number average MW
• Number average degree of polymerization
• Weight average MW How to find Mn?
1. Calculate xiMi
2. Sum these!
molgM n /150,21
Number average MW (Mn)
MW range (g/mol) Mean (Mi)
Min Max xi (g/mol)
5000 10000 0.05 7500
10000 15000 0.16 12500
15000 20000 0.22 17500
20000 25000 0.27 22500
25000 30000 0.20 27500
30000 35000 0.08 32500
35000 40000 0.02 37500
xiMi (g/mol)
375
2000
3850
6075
5500
2600
750

Example Problem 4.1
Number average degree of polymerization
– (MW of H2C=CHCl is 62.50 g/mol)
m
M
n
n
n 
MW range (g/mol) Mean (Mi)
Min Max wi (g/mol)
5000 10000 0.02 7500
10000 15000 0.10 12500
15000 20000 0.18 17500
20000 25000 0.29 22500
25000 30000 0.26 27500
30000 35000 0.13 32500
35000 40000 0.02 37500
How to find Mw?
1. Calculate wiMi
2. Sum these!
molgM w /200,23
wiMi (g/mol)
150
1250
3150
6525
7150
4225
750
10.1
/150,21
/200,23

molg
molg
M
M
n
w
338
/50.62
/150,21

molg
molg
Weight average molecular weight (Mw)

DP = average number of repeat units per chain
m
M
DP
n

97
ii mfm
m


:followsascalculatedisthiscopolymersfor
unitrepeatofweightmolecularaveragewhere
C C C C C C C CH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
C C C C
H
H
H
H
H
H
H
H
H( ) DP = 6
mol. wt of repeat unit iChain fraction

Molecular Shape (or Conformation) – chain
bending and twisting are possible by rotation
of carbon atoms around their chain bonds
 note: not necessary to break chain bonds to alter
molecular shape
98
Adapted from Fig.
4.5, Callister &
Rethwisch 3e.
– C-C bonds are typically 109° (tetrahedral, sp3 carbon)
– If you have a macromolecule with hundreds of C-C bonds, this
will lead to bent chains

 Molecular shape
 Taking this idea further, can also have rotations about bonds
 Leads to “kinks”, twists
 “the end-to-end distance of a polymer chain in the solid state (or in
solution) is usually much less than the distance of the fully extended
chain!
 This is not even taking into account that you have numerous chains
that can become entangled!

 4.7 Molecular structure
 Physical properties of polymers depend
not only on their molecular weight/shape,
but also on the difference in the chain
structure
 Four main structures
• Linear polymers
• Branched polymers
• Crosslinked polymers
• Network polymers

101
Branched Cross-Linked NetworkLinear
secondary
bonding

 – polymers in which the mer units are connected end-
to-end along the whole length of the chain
 These types of polymers are often quite flexible
• Van der waal’s forces and H-bonding are the two
main types of interactions between chains
• Some examples – polyethylene, teflon, PVC,
polypropylene
Linear polymers

Branched polymers
• Polymer chains can branch:
• Or the fibers may aligned parallel, as in fibers and some
plastic sheets.
• chains off the main chain (backbone)
– This leads to inability of chains to pack very closely together
» These polymers often have lower densities
• These branches are usually a result of side-reactions during
the polymerization of the main chain
– Most linear polymers can also be made in branched forms

Crosslinked polymers
• Molecular structure
– adjacent chains attached via covalent bonds
• Carried out during polymerization or by a non-reversible reaction
after synthesis (referred to as crosslinking)
• Materials often behave very differently from linear polymers
• Many “rubbery” polymers are crosslinked to modify their mechanical
properties; in that case it is often called vulcanization
• Generally, amorphous polymers are weak and
cross-linking adds strength: vulcanized rubber is
polyisoprene with sulphur cross-links:

Network polymers
– polymers that are “trifunctional” instead of bifunctional
– There are three points on the mer that can react
– This leads to three-dimensional connectivity of the polymer
backbone
• Highly crosslinked polymers can also be classified as network
polymers
• Examples: epoxies, phenol-formaldehyde polymers

2
• Covalent chain configurations and strength:
Direction of increasing strength
POLYMER MICROSTRUCTURE

Classification scheme for the
characteristics of polymer
molecules
4.8 Molecular configurations
isomerism – different molecular
configurations for molecules (polymers) of
the same composition
Stereoisomerism
Geometrical Isomerism

4.8 Molecular Configurations
Repeat unit
R = Cl, CH3, etc
C C
R
HH
H
C C
H
H
H
R
or C C
H
H
H
R
Stereoisomers are mirror
images – can’t superimpose
without breaking a bond
Configurations – to change must break bonds
E
B
A
D
C C
D
A
B
E
mirror
plane

Head to-head
Head to-tail Typically the head-to-tail
configuration dominates

• Stereoisomerism
– Denotes when the mers are linked together in the same way
(e.g. head-to-tail), but differ in their spatial arrangement
– This really focuses on the 3D arrangement of the side-chain
groups
– Three configurations most prevalent
• Isotactic
• Syndiotactic
• Atactic

ISOTACTIC
• Stereoisomerism
– Isotactic polymers
– All of the R groups are on the same side of the chain
C
C
C
C
C
C
C
R R R R
H H H
H H H H
HHH
Isotactic configuration
• Note: All the R groups are head-to-tail
• All of the R groups are on the same side of the chain
• Projecting out of the plane of the slide
• This shows the need for 3D representation to understand
stereochemistry!

SYNDIOTACTIC
• Stereoisomerism
– Syndiotactic polymers
– The R groups occupies alternate sides of the chain
Syndiotactic configuration
• Note: The R groups are still head-to-tail
• R groups alternate – one of out of the plane, one into the plane
C
C
C
C
C
C
C
R H R H
H H H
H R H R
HHH

ATACTIC
• Stereoisomerism
– Atactic polymers
– The R groups are “random”
Atactic configuration
• R groups are both into and out of the plane, no real registry
• Two additional points
• Cannot readily interconvert between stereoisomers – bonds
must be broken
• Most polymers are a mix of stereoisomers, often one will
predominate
C
C
C
C
C
C
C
R R H R
H H H
H H R H
HHH

Stereoisomerism—Head-to-tail
Syndiotactic
conformation
Atactic conformation
isotactic configuration

115
C C
HCH3
CH2 CH2
C C
CH3
CH2
CH2
H
cis
cis-isoprene
(natural rubber)
H atom and CH3 group on
same side of chain
trans
trans-isoprene
(gutta percha)
H atom and CH3 group on
opposite sides of chain

c04eqf18
Geometrical Isomerism

4.9 Plastics
• variety of properties due to their rich chemical
makeup
• They are inexpensive to produce, and easy to
mold, cast, or machine.
• Their properties can be expanded even further
in composites with other materials.

Glass-rubber-liquid
• Amorphous plastics have a complex thermal profile with
3 typical states:
Log(stiffness)
Pa
Temperature
3
9
6
7
8
4
5
Glass phase (hard plastic)
Rubber phase (elastomer)
Liquid
Leathery phase

Thermosetting and Thermoplastic
Polymers
Another way to categorize polymers
how do they respond to elevated temperatures?

120
Thermoplastics –soften when heated, and harden when
cooled – process is totally reversible; melt and solidify
without chemical change
This is due to the reduction of secondary forces between
polymer chains as the temperature is increased
Most linear polymers and some branched polymers are
thermoplastics
They support hot-forming methods such as injection-
molding and FDM.
Thermoplastics
.

THERMOSETS
– harden the first time they are heated, and do not
soften after subsequent heating
• During the initial heat treatment, covalent linkages are formed
between chains (i.e. the chains become cross-linked)
• Polymer won’t melt with heating – heat high enough, it will
degrade
• Network/crosslinked polymers are typically thermosets

THERMOSETS
• irreversibly change when heated are called thermosets.
• Large cross-linking during change (10 to 50% of mers)
• which strengthens the polymer (setting). large cross linking
• Thermosets will not melt, and have good heat resistance.
• They are often made from multi-part compounds and formed before
setting (e.g. epoxy resin).
• Setting accelerates with heat, or for some polymers with UV light.
vulcanized rubber, epoxies, polyester
resin, phenolic resin

4.10 Structures of Polymers
• Copolymers
– Idea – polymer that contains more than one mer unit
– Why? If polymer A has interesting properties, and polymer B has
(different) interesting properties, making a “mixture” of polymer
should lead to a superior polymer
“Random” copolymer – exactly what it sounds like
“Alternating” copolymer – ABABABA…

• Copolymers
– Idea – polymer that contains more than one mer unit
– Why? If polymer A has interesting properties, and polymer B has
(different) interesting properties, making a “mixture” of polymer
should lead to a superior polymer
“Block” copolymers. Domains of “pure” mers
“Graft” copolymers. One mer forms
backbone, another mer is attached to
backbone and is a sidechain (it is “grafted” to
the other polymer)

two or more monomers
polymerized together
 random – A and B
randomly positioned along
chain
 alternating – A and B
alternate in polymer chain
 block – large blocks of A
units alternate with large
blocks of B units
 graft – chains of B units
grafted onto A backbone
A – B –
125
random
block
graft
Adapted from Fig.
4.9, Callister &
Rethwisch 3e.
alternating

 Polymers often have two different monomers along
the chain – they are called copolymers.
 With three different units, we get a terpolymer. This
gives us an enormous design space…

4.11 Polymer structure
• The polymer chain layout determines a lot of material
properties:
• Amorphous:
• Crystalline:

 Ordered atomic
arrangements involving
molecular chains
 Crystal structures in
terms of unit cells
 Example shown
 polyethylene unit cell
128
Adapted from Fig.
4.10, Callister &
Rethwisch 3e.
– Polymers can be crystalline (i.e.
have long range order)
– However, given these are large
molecules as compared to
atoms/ions (i.e. metals/ceramics)
the crystal structures/packing will
be much more complex

• Polymer crystallinity
– (One of the) differences between small
molecules and polymers
– Small molecules can either totally crystallize or
become an amorphous solid
– Polymers often are only partially crystalline
• Why? Molecules are very large
• Have crystalline regions dispersed within the
remaining amorphous materials
• Polymers are often referred to as semicrystalline

• Polymer crystallinity
– Another way to think about it is that these are two
phase materials (crystalline, amorphous)
– Need to estimate degree of crystallinity – many ways
• One is from the density
 
 
100% 



acs
asc
itycrystallin



4.11 Polymer crystallinity
– What influences the degree of crystallinity
• Rate of cooling during solidification
• Molecular chemistry – structure matters
– Polyisoprene – hard to crystallize
– Polyethylene – hard not to crystallize
• Linear polymers are easier to crystallize
• Side chains interfere with crystallization
• Stereoisomers – atactic hard to crystallize (why?); isotactic,
syndiotactic – easier to crystallize
• Copolymers – more random; harder to crystallize

Polymers rarely 100% crystalline
 Difficult for all regions of all chains to
become aligned
132
• Degree of crystallinity
expressed as % crystallinity.
-- Some physical properties
depend on % crystallinity.
-- Heat treating causes
crystalline regions to grow
and % crystallinity to
increase.
(Fig. 14.11 is from H.W. Hayden, W.G. Moffatt,
and J. Wulff, The Structure and Properties of
Materials, Vol. III, Mechanical Behavior, John Wiley
and Sons, Inc., 1965.)
crystalline
region
amorphous
region

• Molecular weight, Mw: Mass of a mole of chains.
4
• Tensile strength (TS):
--often increases with Mw.
--Why? Longer chains are entangled (anchored) better.
• % Crystallinity: % of material that is crystalline.
--TS and E often increase
with % crystallinity.
--Annealing causes
crystalline regions
to grow. % crystallinity
increases.
crystalline
region
amorphous
region
(Fig. 14.11 is from H.W. Hayden, W.G. Moffatt,
and J. Wulff, The Structure and Properties of
Materials, Vol. III, Mechanical Behavior, John
Wiley and Sons, Inc., 1965.)

4.12 Polymer crystals
 Chain folded-model
 Many polymers crystallize as very thin platelets (or lamellae)
 Idea – the chain folds back and forth within an individual
plate (chain folded model)
• Crystalline regions
– thin platelets with chain folds at faces
– Chain folded structure

 Electron micrograph – multilayered single crystals
(chain-folded layers) of polyethylene
 Single crystals – only for slow and carefully
controlled growth rates
135

 Some semicrystalline
polymers form
spherulite structures
 Alternating chain-
folder crystallites and
amorphous regions
 Spherulite structure
for relatively rapid
growth rates
136
Spherulite
surface

• Polymer crystals
– More commonly, many polymers that crystallize from a melt form
spherulites
• One way to think of these – the chain folded lamellae have
amorphous “tie domains” between them
• These plates pack into a spherical shape
• Polymer analogues of grains in polycrystalline
metals/ceramics

138
Cross-polarized light used
-- a maltese cross appears in each spherulite

The Outline
• Reactions of polymers
Addition Polymerization
Step Growth Polymerization
• Kinetic Of Polymerization
• Polymerization Processes
Bulk Polymerization
Solvent Polymerization
Suspention Polymerization
Emulsion Polymerization
Special Processes

The Outline
• Chemical and Physical Structures of Polymers
• Polymer’s molecular structures
Confriguration and conformation of polymers
Chain structures of polymers
• Physical Structures of Polymers
Polymer crystallinity
Crystallinity and amorphousness of polymers

Outline
• Types of Polymers and Polymer Processing
• Members of Polymers
Definition of Thermosets & Thermoplastics
Common products and their properties
• Forming Techniques of Polymers
Extrusion of polymers
Injection Molding
Blow Molding
Thermoforming
Compression Molding
Casting

The Outline
• Recycling of Polymers
Definiton of Recycling
Why is recycling important?
Benefits
Recycling of polymers

Addition Polymerization (Chain Growth)
Step Growth Polymerization
(Condensation)

Differences between step-growth
polymerization and chain-growth
polymerization
Step-growth polymerization Chain-growth polymerization
Growth throughout matrix Growth by addition of monomer only at
one end of chain
Rapid loss of monomer early in the
reaction
Some monomer remains even at long
reaction times
Same mechanism throughout Different mechanisms operate at
different stages of reaction (i.e.
Initiation, propagation and
termination)
Average molecular weight increases
slowly at low conversion and high
extents of reaction are required to
obtain high chain length
Molar mass of backbone chain increases
rapidly at early stage and remains
approximately the same throughout the
polymerization
Ends remain active (no termination) Chains not active after termination
No initiator necessary Initiator required

Step of Radical Chain
Polymerization
• Initiation
• Propagation
• Termination

TERMINATION
Dead Polymer
i.) Coupling or Combination;
ii.) Disproportionation

CHAIN TRANSFER
REACTIONS
Transfer to monomer reaction
Transfer to initiator reaction
Transfer to solvent reaction

IONIC CHAIN POLYMERIZATION
• Using catalyst, not initiator
• Highest reaction rate
• Termination step is just disproportionation
• Environment must be pure
• Reaction occurs in the cold

Anionic Polymerization=Living Polymerization
If the starting reagents are pure and
the polimerization reactor is purged of
all oxygen and traces of water,
polimerization can proceed until all
monomer is consumed.

CONDENSATION
POLYMERIZATION
• Using catalyst
• Minumum two functional groups required
• Usually linear
• Molecular weight increases slowly at low
conversion
• High extents of reaction are required to

KINETICS OF
POLYMERIZATION
• Reaction rate of ionic polimerization more
than radicalic polimerization
• So kinetics of ionic polimerization are not
calculated
• But kinetics of radicalic polimerization can
be analysed

Kinetic of Radicalic
Polymerization
Initiation;
Propagation;
Termination;

Kinetic of Radicalic
Polymerization
• Ro = overall rate
of polimerization
• Rp = rate of chain
propagation
• Ri = rate of
initiation step
• Rt = rate of

Kinetic of Condensation
Polymerization
• Equivalent reactivity
of functional groups.
• It may be first,
second or third order
by depending upon.

Kinetic of Condensation
Polymerization
• Assumption = a stoichiometry balance of monomer concentration

POLYMERIZATION
PROCESSES
• Bulk Polymerization
• Solvent Polymerization
• Suspention Polymerization
• Emulsion Polymerization
• Special Processes
 Electrochemical Polymerization
 Radiation Polymerization
 Grow-discharge (Plasma)

Bulk Polymerization
• The simplest technique
• It gives the highest-purity polymer
 Ingredients : monomer,
monomer-soluble initiator,
perhaps a chain transfer agent
Advantages Disadvantages
High yield per reactor volume Difficult of removing the lost
traces of monomer
Easy polymer recovery Dissipating heat produced during
the polimerization
Final product form

Solution Polymerization
 Ingredients : monomer
initiator
solvent
• Heat can be removed by conducting the polymerization in an organic solvent or
water
• Initiator or monomer must be soluble in solvent
• Solvents have acceptable chain-transfer characteristics
• Solvents have suitable melting or boiling points for the conditions of
polymerization
Advantages Disadvantages
Temperature control is easy Small yield per reactor volume
Easy removed Solvent recovery

Suspention Polymerization
• Coalescense of sticky droplets is prevented by PVA
• Near the end of polymerization, the particles harder and they can
be removed by filtration, then washing
 Ingredients : water-insoluble monomer,
water-insoluble initiator,
sometimes chain transfer agent
suspention medium (water-usually)
Advantages (according to bulk
polymerization)
Disadvantages
Forming process not using Polymer purity is low
Stirring is easy Reactor capital costs are higher
than for solution polymerization
Separation process is easy

Emulsion Polymerization
• Particles are formed monosize with emulsion polymerization
• Polymerization is initiated when the water-soluble radical
enters a monomer-containing micelles.
 Ingredients : water-insoluble monomer,
water-soluble initiator,
chain transfer agent,
dispersing medium (water),
fatty acid,
surfactant such as sodium salt of a long chain

Molecular structure of polymers
Typical structures are :
• linear (end-to-end, flexible, like PVC, nylon)
• branched
• cross-linked (due to radiation, vulcanization)
• network (similar to highly cross-linked structures,termosetting
polymers)
Figure1. Schematic representation of (a) linear, (b and c) branched,and (d and e) cross-linked polymers.
The branch points and junction points are indicated by heavy dots (Plastic TechnologyHandbook-ManasChanda Salil K. Roy)

Chemical Structure of Polymers
Molecular configuration of polymers
• Side groups atoms or molecules with free bonds, called free-radicals, like H, O,
methyl affects polymer properties.
Stereoregularity describes the configuration of polymer chains :
• Isotactic is an arrangement where all substituents are on the same side of the
polymer chain.
• Syndiotactic polymer chain is composed of alternating groups
• Atactic the radical groups are positioned at random
Figure 2: Isotactic Syndiotactic and Atactic combinations of a stereoisomers of polymer chain
(http://www.microscopy-uk.org.uk/mag/imgsep07/atactic.png)

FIGURE.3. Diagrams of (a) isotactic, (b) syndiotactic, and (c) atactic configuration in a vinyl polymer.
The corresponding Fischer projections are shown on the right.
(Plastic Technolgoy Handbook)

Table 1. Properties of Polypropylene Stereoisomers
(Plastic Technology Handbook)

Geometrical isomerism:
• The two types of polymer configurations are cis and trans. These structures
can not be changed by physical means (e.g. rotation).
• The cis configuration  substituent groups are on the same side of a carbon-
carbon double bond.
• Trans  the substituents on opposite sides of the double bond.
Figure4.cis trans configurations of polyisoprene
( http://openlearn.open.ac.uk/file.php/2937/T838_1_019i.jpg )

Conformations of a Polymer Molecule
• Conformation The two atoms have other atoms or groups attached
to them configurations which vary in torsional angle are known as
conformations (torsional angle:The rotation about a single bond which
joins two atoms )
• Polymer molecule can take on many conformations.
• Different conformation different potential energies of the
moleculeSome conformations: Anti (Trans), Eclipsed (Cis), and Gauche (+
or -)

Other Chain Structures
• Copolymers polymers that incorporate more than one kind of
monomer into their chain (nylon)
• Three important types of copolymers:
• Random copolymer contains a random arrangement of the multiple
monomers.
• Block copolymer contains blocks of monomers of the same type
• Graft copolymer contains a main chain polymer consisting of one type
of monomer with branches made up of other monomers.
• Figure 5 :Block Copolymer Graft Copolymer Random Copolymer
http://plc.cwru.edu/tutorial/enhanced/FILES/Polymers/struct/struct.htm

Physical Characteristics of
Polymers
• The melting or softening temperature ↑ molecular weight ↑
• The molecular shape of the polymer has influence on the elastic
properties. ↑ coils the ↑ elasticity of the polymer
• The structure of the molecular chains has an effect on the strength
and thermal stability. ↑ crosslink and network structure within the
molecule ↑ the strength and thermal stability.

Polymer Crystallinity
• Crystallinity is indication of amount of crystalline region in polymer
with respect to amorphous content
• X-ray scattering and electron microscopy have shown that the
crystallites are made up of lamellae which,in turn, are built-up of
folded polymer chains
• Figure.6 Schematic representation of (a) fold plane showing regular chain folding, (b) ideal stacking oflamellar
crystals, (c) interlamellar amorphous model, and (d) fringed micelle model of randomly distributed crystallites
• (Plastic Technology Handbook)

Polymer crystallinity
• Crystallinity occurs when linear polymer chains are structurally
oriented in a uniform three dimensional matrix. Three factors that
influence the degree of crystallinity are:
• i) Chain length
ii) Chain branching
iii) Interchain bonding
Figure 7: Crystalline chain
http://plc.cwru.edu/tutorial/enhanced/FILES/Polymers/orient/Orient.htm

Polymer cristallinity
Crystallinity influences:
Hardness,modulus tensile, stiffness, crease, melting point of polymers.
• Most crystalline polymers are not entirely crystalline. The chains, or
parts of chains, that aren't in the crystals have no order to the
arrangement of their chains
• Crystallinity makes a polymers strong, but also lowers their impact
resistance
• Crystalline polymers are denser than amorphous polymers, so the
degree of crystallinity can be obtained from the measurement of
density  Wc=Φcρc/ ρ
ρ  density of entire sample
ρc  density of the crystalline fraction.
Φc volume fraction
Wc mass fraction

Determinants of Polymer Crystallinity
• The degree of crystallinity of a polymer depends on the rate of cooling
during solidification as well as on the chain configuration.
• In most polymers, the combination of crystalline and amorphous
structures forms a material with advantageous properties of strength
and stiffness.
Figure 8: Mixed amorphous crystalline macromolecular polymer structure
(http://web.utk.edu/~mse/Textiles/Polymer%20Crystallinity.htm)

Polymer cristallinity
• Polymer molecules are very large so it might seem that they could not
pack together regularly and form a crystal. Regular polymers may
form lamellar crystals with parallel chains that are perpendicular to
the face of the crystals.
• A crystalline polymer consists of the crystalline portion and the
amorphous portion. The crystalline portion is in the lamellae, and the
amorphous portion is outside the lamellae .
Figure 9. Arrangement of crystalline and amorphousportions
http://pslc.ws/mactest/crystal.htm#structure

Cristillanity and amorphousness
• An amorphous solid is formed when the chains have little orientation
throughout the bulk polymer. The glass transition temperature is the
point at which the polymer hardens into an amorphous solid.
• In between the crystalline lamellae,regions with no order to the
arrangement of the polymer chains  amorphous regions
• Polyethylene can be crystalline or amorphous. Linear polyethylene is
nearly 100% crystalline. But the branched polyethylene is highly
amorphous.
Figure 10.Linear and Branched Polyethylene
(http://pslc.ws/macrog/kidsmac/images/pe03.gif )

Examples...
• Highly crystalline polymers:
Polypropylene, Nylon, Syndiotactic polystyrene..
• Highly amorphous polymers:
Polycarbonate, polyisoprene, polybutadiene
• Polymer structure and intermolecular forces has a major role of a
polymer’s crystallinity.

Classification of Polymers
…with regard to their thermal processing behavior ;
• Thermoplastic Polymers (Thermoplastics)
soften when heated and harden when cooled
• Thermosetting Polymers (Thermosets)
once having formed won’t soften upon heating

Thermoplastics
• have linear or branched structure
chains are flexible and can slide past each other

• have strong covalent bonds and weak intermolecular van
der Waals bonds
• elastic and flexible above glass transition temperature
• can be heat softened, remolded into different forms
• reversible physical changes without a change in the
chemical structure

Thermosets
• chains chemically linked by covalent bonds
• hardening involves a chemical reaction which
connects the linear molecules together to form a
single macromolecule.

Thermosets
• once polymerization is complete, cannot be softened, melted
or molded non-destructively.
• have higher thermal, chemical and creep resistance than
thermoplastics
• Thermosets suitable materials for
Composites
Coatings
Adhesive applications

Common thermoplastics
Commodity Polymers
POLYETHYLENES
POLYPROPYLENE
POLYSTYRENE
POLYVINYLCHLORIDE-PVC
POLYMETHYLMETHACRYLATE-PMMA
Engineering Polymers(have a thermal resistance 100-150°C)
POLYCARBONATE
NYLON(POLYAMIDE)
POLYETHYLEN TEREPHATALATE-PET
High Performance Polymers (have a thermal resistance >150°C)
POLYTETRAFLUOROETHYLENE-teflon
POLYARYLETHERKETONES-PEEK

POLYETHYLENE
• prepared directly from the polymerization of ethylene (C2H4).
• two main types are; low-density (LDPE) and high-density
polyethylene (HDPE)
• Advantages
cheap
good chemical resistance
high impact strength

• Limitations
low heat resistance (upper temperature limit is 60°)
degrade under UV irradiation.
high gas permeability, particularly CO2
– Applications
extensively for piping and packaging
chemically resistant fittings, garbage bags
containers, cable covering

POLYPROPLYLENE
• improved mechanical properties compared to polyethylene;
has a low density (900–915 kg/m3), harder, and has a higher
strength
Good chemical and fatigue resistance
• Disadvantages
Oxidative degradation, high thermal expansion,
high creep poor UV resistance
– Applications
medical components, films for packaging (e.g. cigarette
packets)reusable containers, laboratory equipment

POLYSTYRENE
• a light amorphous thermoplastic
• Advantages
low cost, easy to mould, rigid, transparent
no taste, odor, or toxicity, good electrical insulation
– Disadvantages
sensitive to UV irradiation (e.g. sunlight exposure)
chemical resistance is poor, brittle
– Applications
CD-DVD cases, electronic housings, food packaging, foam
drink cups and egg boxes

• was the first thermoplastic used in industrial applications
• very resistant to strong mineral acid and bases, good
electrical insulators, flame-retardant
• Two grades of the PVC material are available:
rigid PVC is used in the construction industry for piping
cold water and chemicals
flexible PVC is used in wire and cable coating, paints, signs

Common thermosets
• EPOXIES
• UNSATURATED POLYESTERS
• PHENOL FORMALDEHYDE (PHENOLIC)
• POLYURETHANES

EPOXIES
• Advantage
mechanically strong, highly adhesive
good chemical and heat resistance
electrical insulators
• Disadvantage
expensive
• Applications
as industrial adhesives, coatings or as matrices in
advanced
reinforced plastics and also as encapsulation media

UNSATURATED POLYSTERS
• Advantage
hard, high strength
cheap compared to Epoxy
good electrical insulator
high heat resistance
• Disadvantage
poor solvent resistance compared to other thermosets
• Applications
molding or casting materials for a variety of electrical
applications, matrix for composites such as fiberglass
boats, fences, helmets, auto body components

PHENOLICS
• most commonly used thermosets
• high hardness, excellent thermal stability;
low tendency to creep
• Applications
wiring devices, bottle caps, automotive parts,
plugs
and switches, as adhesives coatings and
molded
components for electrical applications

POLYURETHANES
• depending on the degree of cross-linking they behave as
thermosets or thermoplastics
• low cost, high impact strength, high adhesion properties
• be processed into coatings, adhesives, binders, fibers and
foams

Methods of polymer fabrication
 Extrusion of polymers
 Injection Molding
 Blow Molding
 Thermoforming
 Compression Molding
 Casting

Extrusion of polymers
• method used mainly for thermoplastics
• is a continuous process as long as raw pellets are supplied
• is a process of manufacturing mostly long products of
constant cross-section;
i.e.. rods, sheets, pipes, films, wire insulation coating

… extrusion
• pelletized material is successively compacted, melted and
formed into a continuous charge of viscous fluid
• temperature of the material is controlled by
thermocouples
• forcing soften polymer through a die with an opening
• the product going out of the die is cooled by blown air or in
water bath

Injection Molding
• most widely used technique for thermoplastics
• highly productive method, profitable in mass production of
large number of identical parts
• polymer in form of pellets is fed into machine and is pushed
forward into a heating chamber then the molten plastic is
forced through a nozzle into the enclosed mold cavity
• pressure is maintained until solidification and then the mold
opens and the part is removed

Blow Molding
• is a process in which a heated hollow thermoplastic tube
(parison) is inflated into a closed mold
• disposable containers, recyclable bottles, automotive fuel
tanks, tubs are produced
• involves manufacture of parison by extrusion, injection or
stretching

• parison in a semi molten state is placed in a two piece mold
having the desired shape
• parison is inflated by air blown, taking a shape conforming
that of the mold cavity
• parison is then cut on the top, mold cools down, its halves
open, and the final part is removed

Thermoforming
• is a process of shaping flat thermoplastic sheet
• softening the sheet by heat, followed by forming it in the
mold cavity
• Thermosets can not be formed by the thermoforming
because of their cross linked structure
• widely used in the food packaging industry; manufacturing of

Thermoforming methods
three thermoforming methods, differing in the forming stage:
1. Vacuum Thermoforming; shaping a preheated thermoplastic
sheet by means of vacuum produced in the mold cavity
2. Pressure Thermoforming;... by means of air pressure.
3. Mechanical Thermoforming;... by direct mechanical force

Thermoforming by vacuum and mechanical
force

Compression Molding
used mostly for molding thermoset resins
• pre-weighed amount of a polymer mixed with additives is
placed into the lower half of the mold
• polymer is preheated prior to placement into heated mold
cavity ,half of the mold moves down, pressing on the polymer
charge and forcing it to fill the mold cavity
• suitable for molding large flat or moderately curved parts;
side panels for automotive, electric housings etc.

Casting
• both thermosets and thermoplastics may be cast.
• molten polymer is poured into a mold and allowed to solidify
• for thermoplastics solidification occurs upon cooling
while thermoset’s hardening is a consequence of
polymerization reaction

REFERENCES
 François Carderelli, Materials Handbook: A Concise Desktop
Reference,2nded.,Springer
 Donald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis
Group
 J. A.Brydson, Plastics Materials, 7thed., Heinemann
 William D. Callister ,Materials Science and Engineering,7th ed., Wiley
 http://www.substech.com
 http://www.azom.com
 http://en.wikipedia.org

Recycling:
A Sector of Solid
Waste Management
http://environment.utk.edu/policy.html

What is Recycling?
Recycling refers to the process of collecting used materials
which is usually considered as ‘waste’ and reprocessing
them. Recycling varies from ‘re-use’ in the sense that
while re-use just means using old products repeatedly,
recycling means using the core elements of an old
product as raw material to manufacture new goods.

Why Recycling is Important?
• Recycling Saves Energy
• Recycling Saves Environmental Conditions and Reduces
Pollution
• Recycling Saves Natural Resources
• Economic Benefits
• Recycling Saves Space for Waste Disposal

Benefits
• Conserves Resources
• Prevents emissions of greenhouse gasses &
water pollutants
• Supplies valuable raw materials to industry
• Saves tax-payer dollars
• Creates jobs
• Stimulates development of greener technologies
• Reduces the need for new landfills and
incinerators

Recycling of polymers
Recycling of Polymers
Mechanical recycling
Chemolysis
Glycolysis
Methanolysis
Hydrolysis
Chemical recycling
Energy recycling
Thermolysis
Pyrolysis
Hydrogenation

Why do we use mechanical, chemical and
energy recycling?
• Hence mechanical recycling is realy best suited to clean plastic
waste,such as packaging material.
•Chemical recycling of waste plastics is important issue.
We have applied reaction in water or organic solvent in
sub- or supercritical condition to convert polymers into its monomers.
Condensed polymers such as polyethylene terephthalate or
nylon 6 were depolymerized to its monomers by hydrolysis of
alcoholysis in supercritical water or alcohol.

Conclusive Facts
1 t = 20,000 plastic bottles
• 25,000 t of bottles recycled in the UK in 2003 saved approximately
25 million kWh of energy
• 25 recycled PET bottles can be used to make an adult’s fleece
jacket
• Recycling a single plastic bottle can conserve enough energy to light
a 60 W lightbulb for up to 6 h

We have done it!!!
Ref: http://www.container-recycling.org/ assets/ppt/1PlasticDebrisConference9.ppt

Study Questions
• Define the following terms:
[Polymer, homopolymer, copolymer, Stereoisomerism, Isotactic polymer, Syndiotactic polymer, etc]
• Respond to the following questions:
 State and explain the classification of polymers
 State and explain the characteristics of ideal polymers
 State and describe nature of pharmaceutical products which use polymers as their
physicochemical components
 Describe the pros and cons of biodegradable polymers in drug delivery process
 Describe the mechanisms involved in polymeric controlled release of drug entities for
therapeutical effects
 Write on the physicochemical nature of polymeric structures .
 What factorial considerations apply to the choice of a polymeric material for drug dosage form
 What are some advantages and disadvantages of polymeric materials over others for dosage form
formulations
• Group work discussional questions:
 Write on the physicochemical nature of polymeric structures .
 What factorial considerations apply to the choice of a polymeric material for drug dosage form
 What are some advantages and disadvantages of polymeric materials over others for dosage form
formulations

Look at the changes you could
make with recycling...
http://environment.utk.edu/policy.html

REFERENCES
 François Carderelli, Materials Handbook: A Concise Desktop
Reference,2nded.,Springer
 Donald Hudgin, Plastics Technology Handbook, 4th ed., Taylor & Francis
Group
 J. A.Brydson, Plastics Materials, 7thed., Heinemann
 William D. Callister ,Materials Science and Engineering,7th ed., Wiley
 Plastic Technology Handbook, 4th Edition, Authors: Manas Chanda,Salil K.
Roy

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