2. Introduction:
• Polymers are derived from GREEK words ; poly – many and meros – units
(or) parts.
• Polymers are the synonym for plastics.
• All plastics are polymers, but not all polymers are plastics.
Eg: n (CH2˭CH2) (-CH2-CH2-)n
Ethylene Polyethylene
• The properties of the polymers depends on their
a) molecular configuration
b) Polymerization
c) Branching
d) Cross-linking.
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3. Definition:
• Polymers are the high molecular weight compounds whose structures
are of a large number of simple repeating units.
• The repeating units are usually obtained from low molecular weight
simple compounds referred as monomers.
• Monomer is a micro-molecule (smaller molecule) which combines with
each other to form a polymer.
eg: ethylene, vinyl chloride, styrene, etc
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4. • Copolymer:
Polymers formed from two or more different monomers are
called as copolymers.
- 𝐴 − 𝐵 − 𝐴 − 𝐵 − 𝐴 − 𝐵 -
• Homo-polymer:
Polymers formed from bonding of identical monomers are called as
homo-polymers.
- 𝐴 − 𝐴 − 𝐴 − 𝐴 − 𝐴 -
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5. Importance of polymer:
• Polymers are used as carrier materials in the formulation of controlled
drug delivery system.
• The selection of the polymer depends upon the intended use and the
desired release profile.
Ideal characteristics of polymer:
1. Inert and compatible with environment.
2. Nontoxic.
3. Easily administrable.
4. Easy and inexpensive to fabricate the dosage form.
5. Good mechanical strength.
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6. Monomers are linked together in different forms to form:
• Linear or branched polymer:
o They are also known as thermoplastic materials.
o They flow when heated.
o They can be fabricated by the application of heat and pressure.
o They are soluble in certain solvents.
oThese polymers consist of a long and straight chains.(linear polymer)
o These polymer contains linear chain with some branches.(branched)
e.g; polyesters, polyamides, polyolefins, LDPE (low density polyethylene),
HDPE(high density polyethylene), etc
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7. • Cross-linked chain polymer:
o These are usually formed from bi-functional and tri-functional
monomer and contain strong covalent bonds between various linear
polymer chain.
o They are also known as thermosetting plastics.
o They can’t be fabricated by the application of heat and pressure.
o Since, all the polymer chains are interconnected by the covalent cross
links, these polymers cannot be dissolved and only swell to the extent
allowed by cross-linking density.
• e.g; Bakelite, melamine.
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8. Classification of polymers:
• Natural
• Semi-synthetic
• synthetic
Based on origin
• Addition polymer
• Condensation polymer
Based on method of
polymerization
• Chain polymerization
• Step-growth polymerization
Based on the
mechanism of
polymerization
Based on the
degradability of
polymer
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9. 1) Classification based on source:
Natural polymer:
These are the polymers found in plants and animals. E.g; proteins,
cellulose, resin, rubber, starch.
Semi-synthetic polymer:
These are generally the cellulose derivative like cellulose acetate
(rayon), cellulose nitrate.
Synthetic polymer:
These are the man-made polymers such as plastic (polythene),
synthetic fibres (nylon-6,6), synthetic rubber (Buna-S)
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10. Polymerization:
It is a process in which a large number of small molecules (monomer) combine to form a big
molecule (polymer) with or without elimination of small molecules of H2O, CH3OH , etc
Degree of polymerization:
The degree of polymerization (n or N) is defined as the number of monomeric units in a
macromolecule or polymer or oligomer molecule.(polymer consist of chain of different length,
hence the average value is taken).
Co-polymerization:
It is defined as the process of combining two polymers that are different.
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11. 2) Based on the method of polymerization:
Addition polymerization :
The repeating unit of the polymer have the same molecular formula
as the monomers
They are prepared by the polymerization of the monomers bearing
≥ 1 double or triple bonds or by the ring opening reactions of the
cyclic structures.
e.g; HDPE (high density poly ethylene), LDPE (low density poly
ethylene), PVC (poly vinyl chloride), PS (polystyrene), poly tetra fluoro
ethylene, poly vinyl acetate.
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12. Condensation polymerization :
These are formed by the successive reactions of the functional
groups
Since, the by-product formed is a smaller molecule, the repeating
units of the polymer have fewer atoms than the monomer.
e.g; polyesters like dacron, mylar, etc
polyamides like nylon-6, nylon-6,6 , perlon, Kevlar, nomex, etc
polyurethanes like spandex, etc
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13. 3) Based on the mechanism of polymerization:
Chain (addition) polymerization:
The polymerization reaction proceeds via
discrete initiation,
propagation and
fermentation steps.
Once the polymerization starts, each polymer chain undergoes rapid
preferential growth in terms of molecular weight with a steady decrease
in monomer concentration.
e.g; vinyl polymers, LDPE, HDPE, PVC, poly styrene, poly tetra fluoro
ethylene, poly vinyl acetate.
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14. Step growth (condensation) polymerization:
In this there are no discrete initiation, propagation and termination steps.
The reaction proceeds via specific reaction between the functional groups
and thus any 2 molecular species with appropriate groups react.
The molecular weight of the polymer increases steadily throughout the
reaction and monomer disappears easily in the reaction.
e.g; polyesters like dacron, mylar, etc
polyamides like nylon-6, nylon-6,6 , perlon, Kevlar, nomex, etc
polyurethanes like spandex, etc
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ACTIVE SITE SYNTHESIS TECHNIQUE
Free radical Free radical polymerization
Carbanion Cationic polymerization
Co-ordination with transition metals Zeigler Natta polymerization
15. 4) Based on the degradability of the polymer:
Degradability of polymer
biodegradable
Natural polymer
Gelatin,
collagen, etc
Synthetic polymer
PGA (poly glycolic
acid), PLA (poly
lactic acid), etc
Non-biodegradable
Semi-synthetic
polymer
EC (ethyl cellulose),
HEC (hydroxy ethyl
cellulose), HPMC,
HPC, etc
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16. Biodegradable polymer:
• The monomers are linked by their functional group & have unstable
linkages in their backbone.
• Polymers are biologically degraded or eroded into oligomer/monomer
by the enzymatic reaction that can be metabolised and excreted.
Ideal characteristics of biodegradable polymer:
should be biocompatible - (shape, surface and leachable)
should be bio absorbable - (degradability profile, reabsorption of
degradation products)
should be bifunctional - (physical, chemical and biological)
should be stable - (processing, sterilization and storage)
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17. • The 3 basic approaches which governs CDDS containing biodegradable
polymer;
1. Erosion of polymer surface with concomitant release of the physically
entrapped drug
2. Cleavage of the covalent bond between the polymer & the drug occurring at
the diffusion drug release
3. Diffusion control release of the physically entrapped drug with bio
absorption of the polymer delayed until drug depletion
Mechanism of release through biodegradable polymer:
Diffusion
Swelling
Erosion
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18. a) Natural polymer:
• They are attractive class of biodegradable polymer.
• Derived from natural sources
• Easily available
• Relatively cheap
• Qualify for a number of chemical modification
• Can be protein on a polysaccharide in chemical origin
• By enzymatic alteration/chemical modification the biodegradation profile
can be increased.
e.g; protein : albumin, collagen, gelatin,etc
polysaccharide : sodium alginate, chitin, chitosan, cellulose, dextran,
inulin, starch, etc
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19. b) Synthetic polymer:
• They are the most attractive class of polymer
• Biocompatible, versatile in terms of physical, chemical and biological
properties.
e.g; aliphatic polyesters: PGA, PLA, poly hydroxy butyrate, poly β-malic
acid
poly phosphoesters
poly anhydride
poly ortho esters
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20. Synthesis of polymer:
Initiation:
It involves the formation of free radical.
Each initiating radical has the ability to attack the double bond of a
monomer.
The radical is transmitted to monomer & monomer radical is formed.
Addition can occur at either end of the polymer.
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Initiation
(birth)
Propagation
(growth)
Termination
(death)
21. Propagation:
The monomer radical is also able to attack
another monomer and so on.
This step is called as chain propagation by
which macroradical is formed.
This entire reaction takes place within a
fraction of a second
Termination:
This reaction ceases the formation of reactive
intermediates in chain propagation
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22. Mechanism of release through biodegradable polymer:
Diffusion
Swelling
Erosion
diffusion:
• The diffusion occur on a macroscopic scale through pores in the polymer
matrix by passing through the polymer chains.
• When the polymer absorbs water it swells in size creating a voids throughout
the interior polymer.
• Smaller drug molecules escape from the void spaces at a known rate
controlled by molecular diffusion
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23. erosion: (e.g; poly anhydride)
• when polymer is exposed to water hydrolysis occurs.
• hydrolysis degrades the large polymers into smaller biocompatible
compounds.
• these smaller compounds diffuse from the interface of the polymer.
• note: these polymers don’t swell.
• the erosion of polymers takes place by:
i. Hydrolytic mechanism
ii. Enzymatic mechanism
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24. a) Hydrolytic mechanism:
• hydrolytic degradation of polymer can be defined as the breaking the
chemical bonds in the polymer by the attack of water to form oligomer and
finally monomers.
• all biodegradable polymers contain hydrolysable bonds like glycosides, esters,
orthoesters, anhydrides, carbonates, amides.
b) Enzymatic mechanism:
• hydrolysis reaction is catalysed by enzymes like proteases, esterases,
glycosidases, etc
• enzymatic degradation occurs when enzymes can’t penetrate the interior of
the polymer, due to high cross-link density forcing the exterior bonds to
cleave first.
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25. swelling:
• these systems are initially dry on the absorption of water/other fluids it
swells
• swelling increases the aqueous contents within the formulation as well as
the polymer mesh size, enabling the drug to diffuse through the swollen
network into external environment.
e.g; ethylene-vinyl alcohol
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27. Application of polymers in controlled drug delivery
system:
lactic acid and glycolic acid are widely used in drug delivery due to
their versatility in polymer properties.
poly-anhydride are used in CDDS because of their unique property of
surface erosion
poly caprolactone is used with other polymer in designing CDDS
poly ortho esters are used in developing implants and oral CDDS
pseudo-amino acids are used in CDDS
hyaluronic acid is used in controlled release ophthalmic preparations.
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