The document discusses various topics related to polymers including their classification, types, mechanisms of polymerization, and methods of polymerization. Polymers can be classified based on their chain structure, chemical composition, source, and backbone. The main types are thermoplastics, thermosets, and elastomers. Polymerization can occur via addition or condensation reactions and methods include bulk, solution, suspension, and emulsion polymerization.
3. Introduction
Monomer (Small molecules)
Linked together to give Polymer
mono →single
mer → single part
Polymer (Large molecules)
poly → many
mer → single part
(Greek) “Macromolecules”
4. 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
5. 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
11. Classification of Polymers
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
14. 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.
15. 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
16. Types of Polymers
Elastomers
intermediate between thermoplastic and thermosetting
polymers
some cross-linking
can undergo extensive elastic deformation
natural rubber, silicone
17. 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.
18. 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
19. Mechanism of Polymerization
Two common types of polymerization
Condensation polymerization (or step-growth
polymerization)
Addition reaction (or chain polymerization)
20. Mechanism of 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
21. Mechanism of Polymerization
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.
22. Mechanism of Polymerization
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
24. Mechanism of Polymerization
Addition Polymerization
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.
26. Polymerization Reaction
Chain Polymerization (Vinyl)
Discrete initiation, propagation & termination
steps
Rapid preferential growth of polymer once
started
Monomer concentration decreases steadily as
polymerization proceeds.
27. Polymerization Reaction
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
28. Polymerization Reaction
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.
29. Polymerization Reaction
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.
30. Polymerization Reaction
Classification of Chain Polymerization (active
centre)
Free radical
Anionic
Cationic
Ziegler-Natta
Chemical structure and nature of substituent on vinyl group
31. 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
32. Chain Polymerization
Free radical Polymerization
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.
34. Chain Polymerization
Free radical Polymerization
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
37. Chain Polymerization
Free radical Polymerization
Chain transfer reaction
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.
42. Chain Polymerization
Free radical 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
48. 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
50. Copolymerization
(a) alternating monomers, (b) random monomers, (c) block copolymers,
and (d) grafted copolymers. Circles of different colors or sizes represent
different monomers.
53. 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
54. 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.
55. 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.
56. 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.
57.
58. 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.
59. Emulsion polymerization
Initiator is insoluble in monomer and soluble in
water
Monomer is insoluble in water
Polymer particle are 0.1 ц in diameter
61. 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
62. Polymer Properties
Molecular weight & Molecular weight distribution
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
63. Polymer Properties
Molecular weight & Molecular weight distribution
Plot of tensile strength against number average molecular
weight for polystyrene
65. Polymer Properties
Polymer hydrophobicity
Hydrophobic polymer
Water impermeable
Water absorption less than 5%
Structural properties like-
Chain stiffness
High degree of crystallinity
Presence of highly hydrophobic groups
66. Polymer Properties
Polymer hydrophobicity
Hydrophilic polymer
Water permeable
Water absorption more than 5%
Structural properties like-
Chain flexibility
absence of crystallinity
Presence of amino, carboxyl, hydroxyl etc groups
71. 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
72. 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.
73. 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
74. 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
75. 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
76. 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.
77. 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
78. 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