2. DEFINITION
The word ‘polymer’ comes from the Greek words
poly (meaning ‘many’) and meros (meaning ‘parts’).
Example: POLYBUTADIENE =
(BUTADIENE+ BUTADIENE+......)n
Where n = 4,000
Polymers are very large molecules made when hundreds of monomers join
together to form long chains.
3. INTRODUCTION
• Polymers are complex and giant molecules usually with
carbons building the backbone, different from low
molecular weight compounds.
• The small individual repeating units/moleules are known
as monomers(means single part).
• 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
• This kind of polymer is known as HOMOPOLYMER.
4. CONT…..
• 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 / HOMOPOLYMER.
5.
6. Molecular Structure of Polymer
Linear
– High Density Polyethylene (HDPE), PVC, Nylon,
Cotton
Branched
– Low Density
- Polyethylene (LDPE)
Cross-linked
– Rubber
Network
– Kevlar, Epoxy
7. CHARACTERISTICS OF
IDEAL POLYMER
• Should be inert and compatible with
the environment.
• Should be non-toxic.
• Should be easily administered.
• Should be easy and inexpensive to
fabricate.
• Should have good mechanical
strength.
8. POLYMERISATION
• The process by which the monomer molecules are linked
to form a big polymer molecule is called ‘polymerisation’.
• Polymerization is a process of bonding monomer, or
“single units” together through a variety of reaction
mechanisms to form longer chains named Polymer
• As important as polymers are, they exist with monomers,
which are small, single molecules such as hydrocarbons
and amino acids.
9. Addition Polymerization=
When monomers just add on to form the polymer, the
process is called ‘addition polym erisation’. The polymer
is the only product
e.g. Ethylene monomers add on to form
polyethylene. (5 Ethylene monomers)
Polyethylene formation
10. It Is useful to dIstInguIsh four
polymerIzatIon procedures fIttIng
thIs general descrIptIon.
• Radical Polymerization The initiator is a radical, and the
propagating site of reactivity (*) is a carbon radical.
• Cationic Polymerization The initiator is an acid, and the
propagating site of reactivity (*) is a carbocation.
• Anionic Polymerization The initiator is a nucleophile, and
the propagating site of reactivity (*) is a carbanion.
• Coordination Catalytic Polymerization The initiator is a
transition metal complex, and the propagating site of
reactivity (*) is a terminal catalytic complex.
11. CONT….
Condensation polymerisation=
• The molecules do not just add on but also undergo some reaction in
forming the polymer, the process is called ‘condensation
polymerisation’.
• Here the two molecules condense to form a polymer.The
condensation takes place between two reactivefunctional groups,
like the carboxyl group(of an acid) and the hydroxyl group(of an
alcohol). While forming the polymer water molecules also get
eliminated.
• In A. P. mol. weight of polymer is roughly equal to that of all
monomers, while in C. P. the mol. weight of polymer is lesser by the
weight of simple molecules eliminated during the condensation
process. E.g. Condensation polymerization diacid
diamine.
12.
13. 1. Natural and Synthetic Polymers
Polymers which are isolated from natural materials,
are called as ‘natural polymers’.
E.g. : Cotton, silk, wool, rubber.
natural rubber
Polymers synthesized from low molecular weight
compounds, are called as, ‘synthetic polymers’.
E.g. polyethylene, nylon, terylene.
Polyethylene
15. 2. Organic and Inorganic
Polymers
A Polymer whose backbone chain is essentially made of
carbon atoms is termed an ‘Organic polymer’.
Examples- cellulose, proteins, polyethylene, nylons.
A Polymer which does not have carbon atom in their
chain is termed as ‘Inorganic polymer’ .
Examples- Glass and silicone rubber
16. 3. Thermoplastic and Thermosetting
Polymer
Some polymer are soften on heating and can be converted into
any shape that they can retain on cooling.
Such polymer that soften on heating and stiffen on cooling are
termed as `thermoplastic’ polymers.
Ex. Polyethylene, PVC, nylon, sealing wax.
Polymer that become an infusible and insoluble mass on heating
are called ‘thermosetting’ polymers. Plastics made of these
polymers cannot be stretched, are rigid and have a high melting
point.
17. 4. Plastics, Elastomers, Fibres & Liquid
resins
Polymer is shaped into hard and tough utility articles by application
of heat and pressure, is known as ‘plastics’.
E.g. polysterene, PVC, polymethyl methacrylate.
When plastics are vulcanised into rubbery products exhibiting good
strength and elongation, polymers are known as ‘elastomers’.
E.g. silicone rubber, natural rubber, synthetic rubber, etc.
Long filament like material whose length is atleast 100 times it’s
diameter, polymers are said to be ‘fibres’.
E.g. Nylon, terylene.
Polymers used as adhesives, potting compounds, sealants, etc., in
a liquid form are described as ‘liquid resins’.
E.g. Epoxy adhesives and polysulphides sealants.
18. Common Addition Polymers
Structure Chemical Name Trade Name or
CommonName
poly(tetrafluoroethylene) Teflon
polypropylene Herculon
polyisobutylene butyl rubber
polyethylene
19. STEPS FOR SYNTHESIS
OF POLYMERS
There are three significant reactions that take place in addition
polymerization:
20. 1. INITIATION
INITIATOR:
• A relatively unstable molecule that decomposes into a
free radical. Used to "initiate" a polymer growth reaction.
(A molecule with an unpaired electron, making it highly
reactive).
• The stability of a radical refers to the molecule's
tendency to react with other compounds. An unstable
radical will readily combine with many different
molecules. However a stable radical will not easily
interact with other chemical substances.
21. CONT….
• The first step in chain polymerization- Initiation involves
the formation of a free radical. Addition can occur at
either end of the monomer. This process is illustrated in
the following animation in which a chlorine atom
possessing an unpaired electron (often indicated as cl-)
initiates the reaction.
22. .
2. PROPAGATION
• Propagation is the middle step in chain polymerization where
successive monomers are attached to the growing chain. In the
propagation stage, the process of electron transfer and
consequent motion of the active center down the chain proceeds.
• In following reaction(chain), refers to a chain of connected
monomers, and X refers to a substituent group (a molecular
fragment) specific to the monomer. For example, if X were a methyl
group, the monomer would be propylene and the polymer,
polypropylene.
• The entire propagation reaction usually takes place within a fraction
of a second.
23. 3. TERMINATION
• Termination of reaction is nothing but stop the further
propagation of chain.
• In theory, the propagation reaction could continue until
the supply of monomers is exhausted. Most often the
growth of a polymer chain is halted by the termination
reaction. Termination typically occurs in two ways:
Combination occurs when the polymer's growth is
stopped by free electrons from two growing chains that
join and form a single chain. The following diagram
depicts combination, with the symbol (R) representing
the rest of the chain.
Combination Disproportionation
24. CONT….
Disproportionation halts the propagation reaction when
a free radical strips a hydrogen atom from an active
chain. A carbon-carbon double bond takes the place of
the missing hydrogen.
- Disproportionation can also occur when the radical
reacts with an impurity. This is why it is so important that
polymerization be carried out under very clean
conditions.
25. LIVING POLYMERISATION
• There exists a type of addition polymerization that does
not undergo a termination reaction. This so-called "living
polymerization" continues until the monomer supply has
been exhausted. When this happens, the free radicals
become less active due to interactions with solvent
molecules. If more monomers are added to the solution,
the polymerization will resume.
• Uniform molecular weights (low polydispersity) are
characteristic of living polymerization. Because the
supply of monomers is controlled, the chain length can
be manipulated to serve the needs of a specific
application. This assumes that the initiator is 100%
efficient.
26. MOLECULAR WEIGHT
DETERMINATION
• There are two ways to calculate the average molecular
weight:
1. Number Average Molecular Weight
2. Weight Average Molecular Weight
27. CONT…
1. Number Average Molecular Weight
• 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.
∑
∑=
i
ii
N
MN
nM
28. CONT…
2. Weight Average Molecular Weight
• Mw- weight average molecular weight.
• Mi- total molecular weight of monomer.
• Ni- number of monomer molecules.
∑
∑=
ii
ii.i
MN
MMN
wM
29. APPLICATIONS
Mainly used for drug delivery.
– As a coating material
examples: Hydroxyl propyl methyl cellulose(HPMC),
Methyl cellulose,
Propylene glycol.
– As a binders in tabletting granulation
examples: Acacia, Gelatin, Sodium alginate.
– As a disintegrants
examples: starch, HPMC
– As a thickening agent in suspension and ophthalmic preparations
Example: methyl cellulose.
– To form bases in ointments.
– In hard and soft capsule gelatin is used.
– Gelatin also used as suppository base, as an emulsifying agent and
suspending agent.
30. THERMAL
CHARACTERIZATION
Thermal analysis of the polymers is the
important phenomenon to study the
stability and degradation of polymers.
Method :-
a) TGA
b) DSC
c) Thermo mechanical analysis
31. Thermo-gravimetric Analysis (TGA)
• This method provides indication for thermal
stability and upper limit of thermal degradation
where loss of sample begins.
• This method only measures loss of volatile
content from the polymer.
• This method has limitation that it can not detect
temperature at chain cleavage of chain takes
place.
32. Differential Scanning Calorimetry
(DSC)
Parameters measured-
1. Glass transition temperature (Tg)
2. Crystalline melting point
3. Heat of fusion
4. Heat of crystallization
• It requires placing of Reference and test sample
for the continuous monitoring in the heating
chamber.
33. Thermo Mechanical Analysis
(TMA)
• This method is used for determination of
deformation of polymer sample as a function of
temperature placed on platform in contact with
probe.
• It measures transition from glassy to a rubbery
polymer and gives idea about softening
temperature.
34. 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.
• Material progressively releasing dissolved or dispersed
drug, with ability of functioning for a temporary period
and subsequently degrade in the biological fluids under a
controlled mechanism, in to product easily eliminated in
body metabolism pathway.
35. Classification
• Biodegradable polymers can be classified in two:
1. Natural biodegradable polymer
examples:
a) Collagen
b) Albumin
c) Casein
d) gelatin
e) xanthum gum
f) gaur gum
g) chitosan
h) chtin
2. Synthetic biodegradable polymer
examples: Polyanhydrides, Poly(ß-Hydroxybutyric Acids) etc.
• Synthetic biodegradable polymer are preferred more than the natural
biodegradable polymer because they are free of immunogenicity & their
physicochemical properties are more predictable &reproducible
36. ADVANTAGES
• Localized delivery of drug
• Sustained delivery of drug
• Stabilization of drug
• Decrease in dosing frequency
• Reduce side effects
• Improved patient compliance
• Controllable degradation rate
