2. Polymer
“Polymer” word is derived from Greek roots “Polus” meaning
many and “Meros” meaning parts.
Definition :
Polymers are high molecular weight chemical compounds
(macromolecules) assembled from a large number of
repeating units called as monomers.
3. Classification of polymers
1. Based on nature of monomers
a) Homopolymers
b) Copolymers
2. Based on the arrangement of monomers
a) Random copolymers
b) Graft copolymers
c) Block copolymers
3. Based on the structure of the polymers
a) Linear
b) Branched
c) Cross-linked
4. Based on thermal response and polymer
property
a) Thermoplastics
b) Thermosets
c) Elastomers
5. Based on the source
a) Natural Polymers
b) Semisynthetic polymers
c) Synthetic polymers
4. 6. Based on the form and use
a) plastics
b) Elastomers
c) Fibers
d) Liquid resins
7. Based on bio-stability
a) Biodegradable polymers e.g. polyesters, proteins,
carbohydrates
b) Non-biodegradable polymers e.g. ethyl cellulose,
HPMC, acrylic polymers, silicones.
5. Copolymer:
Polymer formed from two or more different monomers is called as
copolymer.
- [A – B – A – B – A – B] –
Homopolymer:
Polymer formed from bonding of identical monomers is called as
homopolymer.
- [A – A – A – A – A] –
6. Characteristics for Ideal Polymer
Should be inert and compatible with theenvironment.
Should benon-toxic.
Should be easilyadministered.
Should be easy and inexpensive tofabricate.
Should have good mechanicalstrength.
Should provide drug attachment and release sites for drug
polymer linkages.
7. Applications in Conventional Dosage Forms
Tablets :
- As binders
- Tomask unpleasant taste
- For enteric coated tablets
Liquids:
- Viscosity enhancers
- For controlling the flow
Semisolids :
- In the gel preparation
- In ointments
In transdermal Patches
8. Applications in Controlled Drug Delivery
Reservoir Systems
- Ocusert System
- Progestasert System
- Reservoir Designed Transdermal Patches
Matrix Systems
Swelling Controlled Release Systems
Biodegradable Systems
Osmotically controlled Drug Delivery
9. Biodegradable Polymers
Definition :
Biodegradable polymers are defined as polymers comprised of
monomers linked to one another through functional groups
and have unstable links in the backbone.
They slowly disappear from the site of administration in
response to a chemical reaction such as hydrolysis.
10. Synthetic Polymers :
a) Aliphatic polymers
b) Polyphospho-esters
c) Polyanhydrides
d) Polyorthoesters
Natural Polymers :
a) Collagen
b) Albumin
c) Casein
d) gelatin
Environment Responsive Polymers :
a) Thermo-sensitive – Poly acryl amide
b) pH sensitive – Methyl vinyl ether
11. Mechanism of Biodegradation
A. Hydrolytic Degradation :
Breakdown of polymer by water by cleaving long
chain into monomeric acids. This is done by two
ways:
a)Bulk eroding polymers e.g. Polylactic acid
(PLA),Polyglycolic acid (PGA)
b) Surface eroding polymers e.g. Polyanhydrides
B. Enzymatic Degradation :
Exact mechanism is not known but may be due to
lysis of long polymer chain by attaching to it.
12. Factors affecting Biodegradation
Polymermorphology
pH & ionicstrength
Drug – polymer interaction
Chemical composition andstructure
Processing methods andconditions
Presence of chain defects
