Polymer science

Mr. K K MaliMr. K K Mali
Assistant ProfessorAssistant Professor
Yashoda Technical Campus, SataraYashoda Technical Campus, Satara

Content
Introduction
Classification
Types of Polymers
Applications of polymers
Mechanism of Polymerization
Polymerization Reactions
Methods of Polymerization
Characterization of polymers
Thermodynamics of polymer solution

Introduction
Monomer (Small molecules)
Linked together to give Polymer
mono →single
mer → single part
Polymer (Large molecules)
poly → many
mer → single part
(Greek) “Macromolecules”

Introduction
Macromolecule that is formed by linking of repeating
units through covalent bonds in the main backbone
Properties are determined by
Length
Molecular weight
Backbone structure
Side chains
Resulting macromolecules have huge molecular
weights

Introduction
Polymerization
Process of formation of macromolecules by linking
number of monomers together
Degree of Polymerization (DP)
Average molecular weight of the polymer divided by
the molecular weight of the monomer

Classification of Polymers
By Chain Structure
By Chemical Composition
By Polymer Architecture
By Source
By Backbone

By Chain Structure
 Linear polymer (e.g., high density Polyethylene)
 Branched polymer (e.g., low density Polyethylene)
 Network polymer (e.g., cross linked polymers,
elastomer)
 cross-linked polymers(e.g., melamine formaldehyde resin)

By Chemical Composition
Homopolymer
 Contain a single kind of monomer. Polyethylene
Copolymer
 Contain more than one kind of monomer. Nylon-66
( Hexamethylene diamine and adipic acid)
 Random Eg. Poly (styrene – methylmethacrylate)
 Alternating Eg. Nylon
 Block Eg. Methyl methacrylate
 Graft Eg. Polybutadiene
-A-A-A-A-A-A-A-A-
-A-B-B-A-B-A-A-B-
-A-B-A-B-A-B-A-B-
-A-A-A-A-B-B-B-B-
-A-A-A-A-A-A-A-A-
B-B-B-B-B-B-
Homopolymer
Random copolymer
Alternating copolymer
Block copolymer
Graft copolymer

By polymer architectures
Star polymer: contains ≥3 chains emanating from a core
Eg. Polymethyl methacrylate
Comb polymer: contains pendant chains
Eg. Polyalkyl(meth) acrylates (PAMAs)
Ladder polymer: has recurring fused-ring structures
Eg. Alkyl tri- alkoxyl silane
Semi-ladder polymer: has fused-ring sections interspersed with open-
chain units
Supra-molecular assemblies: molecules linked by non-covalent
bonding

By polymer architectures
Dendrimers
dendritic, starburst.
Dendron (Greek) → tree

By Source
Natural
 MW= 1,50,000 to > 1,000,000
 Polysaccharides like chitosan, Agarose,
 Protein based like Albumin, Gelatin
Synthetic
 Cellulose derivatives like CMC, EC
 Polyanhydrides like Polyadipic acid

By Backbone
With Carbon-chain backbone
Polyethylene
Polypropylene
Polyvinyl Alcohol
With Hetero-chain backbone
Amylase
Cellulose
Polyethylene oxide

Types of Polymers
Thermosetting
Thermoplastic
Elastomer

Types of Polymers
Thermosetting
cross linked polymer
do not flow
can not be reformed or recycled.
presence of extensive crosslink between long chains.
induce decomposition upon heating and renders
thermosetting polymers brittle.
can not dissolve, swell depend on crosslink density
epoxy and polyesters.

Types of Polymers
Thermoplastic
linear, branched polymers, no crosslinks
polymers that flow when heated.
easily reshaped and recycled by heat or pressure due to
presence of long chains with limited or no crosslink
Soluble in certain solvent
polyethylene, polyvinylchloride

Types of Polymers
Elastomers
intermediate between thermoplastic and thermosetting
polymers
some cross-linking
can undergo extensive elastic deformation
natural rubber, silicone

Types of Polymers
Elastomers
(a) When the elastomer contains no cross-links, the application of a force causes both elastic and
plastic deformation; after the load is removed, the elastomer is permanently deformed. (b) When cross-
linking occurs, the elastomer still may undergo large elastic deformation; however, when the load is
removed, the elastomer returns to its original shape.

Types of Polymers
Comparison
BehaviorBehavior General structureGeneral structure ExampleExample
ThermoplasticThermoplastic Flexible linearFlexible linear
chainschains
polyethylenepolyethylene
ThermosettingThermosetting Rigid threeRigid three
dimensional networkdimensional network
polyurethanespolyurethanes
ElastomerElastomer Consist of spring likeConsist of spring like
moleculesmolecules
NaturalNatural
rubberrubber

Mechanism of Polymerization
 Two common types of polymerization
Condensation polymerization (or step-growth
polymerization)
Addition reaction (or chain polymerization)

 Condensation
two monomers react to establish a covalent bond
a small molecule, such as water, HCl , methanol, or CO2
is released.
the reaction continues until one type of reactant is
used up

 Condensation
The molecular structures of the monomers are shown above. The linear
nylon chain is produced when a hydrogen atom from the hexamethylene
diamine combines with an OH group from adipic acid to form a water
molecule.

 Addition Polymerization
monomers react through stages of initiation,
propagation, and termination
initiators such as free radicals, cations, anions opens
the double bond of the monomer
monomer becomes active and bonds with other such
monomers
rapid chain reaction propagates
reaction is terminated by another free radical or
another polymer

The addition reaction for producing polyethylene from ethylene molecules.
The unsaturated double bond in the monomer is broken to produce active
sites, which then attract additional repeat units to either end to produce a
chain.

Polymerization Reaction
 Chain Polymerization (Vinyl)
 Step growth Polymerization

 Chain Polymerization (Vinyl)
Discrete initiation, propagation & termination
steps
Rapid preferential growth of polymer once
started
Monomer concentration decreases steadily as
polymerization proceeds.

 Step growth Polymerization
No discrete initiation, propagation &
termination steps.
Any two molecular species can react.
Polymer molecular weight rises throughout the
reaction.
Monomers disappears earlier

 Comparison
Step Growth Polymerization Chain Polymerization
Growth occurs throughout the matrix
by reaction between monomer,
oligomer & polymers
Growth occurs by successive
addition of monomer units to
limited no. of growing chains
Monomer consumed rapidly while mol.
Wt. increases slowly.
Monomer consumed relatively
slowly but mol. Wt. increases
rapidly.
No initiator needed, same reaction
mechanism throughout.
Initiation & propagation
mechanisms are different.

 Comparison
Step Growth Polymerization Chain Polymerization
No termination steps end groups are
still reactive.
Usually chain termination step is
involved
Polymerization decreases steadily as
functional group consumed
Polymerization rate increases
initially as initiator units generated,
remains relatively constant until
monomer is depleted.
Degree of polymerization is low to
moderate.
Degree of polymerization is very
high.

 Classification of Chain Polymerization (active
centre)
Free radical
Anionic
Cationic
Ziegler-Natta
Chemical structure and nature of substituent on vinyl group

Chain Polymerization
 Free radical Polymerization
 Free radical is a species bearing an odd no of electron
 Unstabilised free radicals are extremely reactive molecules
 Generation of free radical is first step which will then react vinyl
monomer in initiation reaction
 It can be generated by homolytic decomposition of covalent bond energies
about 30-40kcal/mol.
 Three steps:
Initiation
Propagation
Termination

 Initiation
I - I (homolytic decomp of covalent bond with energy 30-40 kcal/mole) 2 I
.
I
.
+ CH2
= CHR I-CH2
-CHR .
 Propagation
I-CH
2
-CHR .
+ CH
2
=CHR
HIGH POLYMER ICH
2
CHRCH
2
CHR.

 Termination
 Coupling
P-CH2
-CHR .
+ .
R CHCH2-P P-CH2CHR-CHR-CH2-P
 Disproportionation
P-CH2
-CHR .
+ .
R CHCH2-P P-CH2CH2R + CR=CH-P

 Termination
Termination occurs in free radical polymerization by one of two mechanisms, combination or
disproportination. Either mechanism involves the reaction between two growing chain ends.
Some monomers terminate exclusively by combination, some by disproportionation, some by
both mechanisms.
Coupling Disproportionation
Two radicals at the chain termini simply
join to form a single bond
The radical at the end of one chain
attacks a hydrogen atom at the carbon
atom in the second chain

 Chain transfer reaction
 Abstraction
P-CH2CHR.
+ P-CH2CHR-P
P-CH2CH2R + P-CH2-CR
.
-P

 Branching
P-CH2-CR
.
-P + CH2=CHR
P-CH2-CR-P Branch growth
CH2
.
C
.
HR

 Hydrogen abstraction
P-CH2CHR.
+ MH P-CH2CH2R+M.
.
 If radical M.
initiates monomer then MH is called as
chain transfer agent. Used to control mol. Wt. of
polymers in controlled amt.

 Anionic

 Anionic
Initiation (by organic bases)
BM B
-
+ M
+
B-
M
+
+ CH
2
=CHR
B-CH
2
CHR
-
M
+

 Anionic
Propagation
B-CH
2
-CHR
-
M
+
+ CH
2
=CHR
B-CH
2
CHRCH
2
CHR
-
M
+

 Anionic polymerisation features
Fast initiation
Slow propagation
No termination
No chain transfer
“living” polymerization

 Cationic polymerisation
Cationic polymerizations are initiated with acids (Proton)
Electron donating substituent is necessary
Nature of counter ion & solvent has an important effect on
polymerization
Chain transfer to monomer or polymer is common

 Initiation
HX + CH
3
-C=CH
2
[CH
3
-C=CH
2
]+
X-
CH3
CH3
{ π-Complex }
+
CH
3
-C-CH
3

 Propagation
CH2R
P-CH2-CH+
+ CH2=CHCH2R
+
CHR X
i)P-CH2-CH2-CH2R + CH2=CH
CH2R CH2R
ii) P-CH=CH + CH3-CH+
x -

 Chain Transfer
+
X-
P-CH
2
CHR + P-CH
2
CHR-CH
2
P
+
X-
PCH
2
CH
2
R + P-CH
2
CRCH
2
P

 Termination
P - CH2
-C+
-CH3
PCH2
C=CH2
+ H+
X-
CH3
X-
CH3

Ziegler-Natta Polymerization
Transition metal catalysts are involved
Example is ethylene
Chain is bound to metal atom with coordinative vacancy
New ethylene molecule is inserted by bonding between C
atom and metal
Active site of growing chain is the C atom bound to the
metal
Branching does not occur
Metal alkyls + transition metal catalyst system

Copolymerization
(a) alternating monomers, (b) random monomers, (c) block copolymers,
and (d) grafted copolymers. Circles of different colors or sizes represent
different monomers.

Polymerization Methods
Bulk polymerization
Solution polymerization
Suspension polymerization
Emulsion polymerization

Bulk polymerization
Advantages Disadvantages
 Simple, only the monomer and
initiator are present in the reaction
mixture
 High molecular weight
• Exotherm of the reaction might
be hard to control
The polymer is soluble
in the monomer:
The polymer is not soluble
in the monomer:
Viscosity of the reaction
increases markedly (gel
effect)
Polymer precipitates
out without increase in
solution viscosity

Solution polymerizationSolution polymerization
Monomers are dissolved in suitable solvent which should be
same for the polymer.
Concentration of monomer is adjusted to control vicosity of
final solution.
Polymer is isolated by solvent evaporation or using nonsolvent
precipitation.

Solution polymerization
Advantages
o Heat evolution can be controlled by external cooling.
Disadvantages
o Excess monomer concentration lead to highly viscous
solution.
o Long heating under vacuum is necessary.

Suspension polymerization
Monomer is dispersed in dispersing medium.
Polymerization occurs in monomer droplets suspended in
medium.
Can be used with free radical polymerization in which
initiator is dissolved in monomer.
Monomer is dispersed in medium using emulsifying agent.

Suspension polymerization
Advantages
o Heat dissipation is not a problem.
o Excessive viscosity build up is not a problem.
o Very high monomer concentration can be used.
o Polymers obtained are spherical in shape.

Emulsion polymerization
Initiator is insoluble in monomer and soluble in
water
Monomer is insoluble in water
Polymer particle are 0.1 ц in diameter

REPRESENTATION OF
EMULSION POLYMERIZATION

Polymer Properties
Molecular weight & Molecular weight distribution
A number-average molecular weight (Mn)
 Molecular weight is determined by calculating the total
molecular weight of monomer and total number of
monomer.
 Mi- total molecular weight of monomer.
 Ni- number of monomer molecules.
 Mn- number average molecular weight
Low MW – less mechanical properties
∑
∑=
i
ii
N
MN
nM

Polymer Properties
A weight average molecular weight Mw
 Mw-weight average molecular weight.
 Mi- total molecular weight of monomer.
 Ni- number of monomer molecules
Low MW – less mechanical properties
∑
∑=
ii
ii.i
MN
MMN
wM

Polymer Properties
 Plot of tensile strength against number average molecular
weight for polystyrene

Polymer Properties
Polymer hydrophobicity
 Hydrophobic polymer
 Hydrophillic polymer
 Water soluble polymer
 Hydrogels

Polymer Properties
 Hydrophobic polymer
 Water impermeable
 Water absorption less than 5%
 Structural properties like-
 Chain stiffness
 High degree of crystallinity
 Presence of highly hydrophobic groups

Polymer Properties
 Hydrophilic polymer
 Water permeable
 Water absorption more than 5%
 Structural properties like-
 Chain flexibility
 absence of crystallinity
 Presence of amino, carboxyl, hydroxyl etc groups

Polymer Properties
 Water soluble polymer
 Water soluble

Polymer Properties
 Hydrogels
 Highly hydrophilic/ Water soluble
 Crosslinked by covalent bonds
 Water absorption more

Polymer Properties
Glass Transition Temperature
Amorphous polymers exists in glassy state- no
molecular motion.
Glassy state- characterised by – hardness, stiffness,
brittleness
As temp raised polymer undergo transition, known as
glass transition temp, Tg, glass to rubbery, flexible,
plastic
Polymer undergoes changes in properties –
permeability, heat content, refractive index, hardness

Polymer Properties
Glass Transition Temperature

Polymer Properties
Crystallinity
Crystalline regions act as crosslinks – stiffen & toughen
the polymer & reduce swelling
Crystalline regions are impermeable to diffusing
molecules- enhancement of crystallinity – decreases
polymer permeability
Crystalline regions are impermeable to water

Polymer Properties
Viscosity:
The dissolved macromolecules have ability to build up the
relative viscosity of their solution.
Solubility :
water soluble polymer interact with water and increase the
viscosity of the solvent
Synersis :
Synersis is a form of instability in aqueous gels and non
aqueous gel in this liquid separate out from a swollen gel
Polymer complex :
polymers from complexes in solution e. g. polyacid mixed
with polyglycols in water.

Polymer Properties
Interaction of polymers with solvent :
A polymer dissolve in liquid completely or swollen by a given
liquid in cross linked polymer solution cannot occur by
imbibition of liquid polymer will swell and from gel
Polymer dissolution:
Dissolution of polymer in solvent is important since it has
many application e.g . Drug delivery plastic recycling
Polymer erosion:
Degradation of polymer is a chemical process erosion is a
physical phenomenon dependent on dissolution and
diffusion process

Polymer Properties
Adsorption of macromolecules:
At the interfaces is used in suspension and emulsion
stabilization
Bioadhesivity of water soluble polymer:
The adhesive performance of polymers is good in case of
carbopol and carboxy methyl cellulose

Polymer Characterization
Molecular Mass
Gel permeation chromatography- molecular weight distribution
Molecular Structure
Ultraviolet-visible spectroscopy, infrared spectroscopy, Raman
spectroscopy, nuclear magnetic resonance spectroscopy, electron
spin resonance spectroscopy, X-ray diffraction, and mass
spectrometry [Functional groups]
Morphology
X-ray diffraction, Transmission Electron Microscopy, Scanning
Transmission Electron Microscopy, Scanning Electron Microscopy,
and Atomic Force Microscopy

Polymer Characterization
Thermal Properties
Differential scanning calorimetry, Dynamic mechanical
spectroscopy and Dielectric spectroscopy
Mechanical Properties
Tensile strength and Young's modulus of elasticity
Viscometry, rheometry, and pendulum hardness.

Applications of Polymer
 Sustained-release dosage form e.g shell for capsulate drug
 Enteric coating. e.g. eudragit
 Film coating. e.g. cellulose acetate phthalate
 Binder. e.g. acacia, gelatin ,ethylcellulosed
 Water soluble polymer .e.g. hydroxypropyl methylcellulose
 Disintegrant.e.g. carboxy –methyl starch
 Protective colloides. e.g. glatin
 Composition of hard and soft gelatin capsule.
 Exipients. e.g. insulin ,heparin
 Containers and closers e.g. Plastic rubber

References
A book of Fundamentals of Polymer Science by Jorge Heller
A text book of Polymer Science by Fred W. Billmeyer
A book of Pharmaceutical Product Development by N. K. Jain
A Primer on Dosage Form Design by NPS Sengar, Ritesh Agrawal,
Ashwini Singh.
Dosage from design, Ritesh Agrawal
Martin’s physical pharmacy and pharmaceutical sciences, by Patrick J
Sinko

Polymer science

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