Introduction to Polymers.

1. A Seminar on
POLYMER SCIENCE
(GENERAL SYNTHESIS)
By: DHIRAJ SHRESTHA
M.Pharma (Pharmaceutics)

2. INTRODUCTION
Derived from Greek word “polus” meaning many and
“meros” meaning parts.
Polymers are very large macromolecules consisting of many
repeating units.
Also k/a Macromolecules.
They are formed by a process called Polymerization, which
links together small molecules called Monomer.
Ex— A gaseous compound called Butadiene gives a polymer
k/a Polybutadiene (synthetic rubber).

3. IDEAL POLYMER
 Ideal polymers must be :-
 Inert to tissues and compatible with environment.
Non toxic and non antigenic.
 Should be bio-degradable and must be eliminated from
the body.
 Should have good mechanical strength, tensile strength,
hydrophobicity and crystallinity.

4. Should have drug attachment site.
Should be easily processed and shaped.
Inexpensive
Readily available
Easily processed on a large scale

5. Classification of polymers
A. Based on source of availability.
B. Based on the structure of polymers.
C. Based on polymerization process.
D. Based on molecular forces.
E. Based on ultimate form and use.

6. General synthesis
1. Bulk polymerization
2. Precipitation polymerization
3. Emulsion polymerization
4. Suspension polymerization
5. Poly-condensation
6. Interfacial poly-condensation

7. Monomer purification
Unsaturated monomers are highly reactive
and can polymerize during transport or
storage.
To avoid such polymerization, they are
transported and stored in an inhibited
condition.
Inhibitors such as hydroquinone or tertiary
butyl catechol are used for this purpose.

8. Monomers are freed of inhibitors by :-
i. Distillation of monomers
ii. Washing with dilute
Saturated monomers containing functional
groups (used for step polymerization)
should be purified to render them free of
non-functional and mono-functional
impurities.

9. 1. Bulk polymerization of Styrene
50mg Azobis isobutyronitrile (AIBN), freshly recrystallized
↓
Add 10ml styrene polymer and swirl
↓
Add 40ml styrene and 500mg Dodecyl mercaptan (DDM)
↓
Flush content with Oxygen free Nitrogen for 15 min.
maintaining flask at 70+ 1°C
↓
Fit water condenser to the flask
↓

10. Remove flask from bath when high viscosity like honey is
attained
↓
Wash flask with toluene and add to a beaker
↓
Stir to form a homogeneous solution
↓
Remove polymer by pouring solution slowly into distilled
methanol under agitation
↓
Wash with methanol and dry under vacuum at 60°C
 Other example :- Methyl methacrylate.

11. 2. Precipitation polymerization
of Acrylonitrile
50mg AIBN dissolved in 50ml acrylonitrile monomer
↓
Add 200ml toluene and flush with nitrogen
↓
Polymerization starts at 70+1°C
↓
After sometimes, turbidity develops and white ppt. starts
collecting at the bottom
↓
Filter, wash with methanol and dried in vacuum at 60°C

12. 3. Suspension polymerization
of Methyl Methacrylate
 Used with free radical polymerizations where the
initiator is dissolved in the monomer and then dispersed
in water using an emulsifying agent.
 Very high monomer conc. can be used.
 Polymers obtained by this method are spheres.
0.1g benzoyl peroxide dissolved in 100g of Methyl
methacrylate in 500ml RBF
↓
Add 180ml distilled water containing 0.02g cetyl dimethyl
benzyl ammonium chloride and 0.05g of PVA

13. ↓
Flush with nitrogen and place on water bath at 75+1°C
↓
In starting, monomer gets dispersed in water phase as tiny
droplets
↓
Continue for 8 hrs
↓
Fine spherical beads of polymethyl methacrylate settle at
the bottom of flask
↓
Filtered and washed with warm water.

14. 4. Emulsion polymerization of styrene
 It is identical to suspension polymerization, but differ in
that the initiator is insoluble in the monomer and
soluble in water.
 Polymer particles produced by this method are typically
0.1µm in diameter.
Take 180ml distilled water in 3 necked RBF
↓
Add 100mg potassium persulfate, 100mg NaHPO4, and
0.1g SLS
↓

15. Pour 100ml styrene in flask and fitted to a water
condenser, high speed stirrer and an inlet tube dipping
into the contents of flasks
↓
Flush Nitrogen gas for few minutes, then remove it and
close mouth with a stopper
↓
Maintain bath temp. at 70+1°C with vigorous stirring
↓
Continue for 4-6 hours
↓
Latex is formed
↓

16. To it add 5ml of 3% sol. of aluminium sulfate
in water
↓
Stir gently till emulsion brokes and coagulate
to give polystyrene
↓
Wash with warm water and methanol and
finally dried in vacuum at 60°C.
 There are 2 important consequences of this unique
polymerization process:-
i. Due to lower frequency of termination, chain growth
can continue for longer periods of time and hence
polymers prepared can have very high molecular
weights.

17. ii. In conventional free radical
polymerization, the propagation rate is
described by —
rp = kp [M] [M·]
Whereas in emulsion polymerization, the rate
is described by-
rp = kp [M] [N/2]
Where [M] is the conc. of monomer,
[M·] is the conc. of radical chain ends,
[N] is the no. of micelles.
 Due to bimolecular termination reaction,
the conc. of free radical chain-ends [M·] is

18. 5. Polycondensation of Ethylene glycol with Maleic acid
Take 500ml of xylene, 62g ethylene glycol, 116g maleic
acid and 1g Þ-toluene sulphonic acid catalyst in 1lit. 3
necked RBF
↓
Add 1-2 fragments of pumic stone
↓
Place flask on an electrical heating mantle with an energy
regulator
↓
Bubble slow stream of CO2 gas by fixing a gas inlet to side
of the neck

19. ↓
To the central neck of flask attach a Dean & Stark
apparatus filled with xylene up to graduated portion and
it is fitted with a Liebig condenser
↓
3rd neck fixed with mercury for the thermometer
↓
Heat flask until its content become homogeneous
↓
When the azetropic vapour mixture condenses at the
receiver part of Dean & Stark apparatus, the xylene and
water separates out and only xylene returns to the
reaction flask
↓

20. Reaction is carried out until 18ml of water is collected
↓
Xylene is separated by distillation
↓
Liquid polymer obtained is purified by washing with
methanol and drying in vacuum at 60°C
↓
Product obtained is an unsaturated polyester
↓
Cured by cross-linking with styrene using a free-radical
indicator.

21. 6. Interfacial polycondensation of Terephthaloyl chloride and
Ethylene diamine
This method can only be applied to very rapid reactions
such as the reaction between an acid chloride and an
amine.
Thus, polyamides can easily be formed by this process
by placing the amine in water and the diacid chloride in
carbon tetrachloride.
20g Terephthaloyl chloride dissolved in 200ml carbon
tetrachloride in 500ml beaker {Solution A}
↓

22. Separately, dissolve 2-3 NaOH pallets in 50ml water and
add 5g ethylene diamine and mix. {Solution B}
↓
Add solution B to solution A slowly
↓
Beaker allowed to stand undisturbed
↓
Opaque film is formed after few minutes at the interface
between the organic and the aqueous layers.
 This is the polyamide formed by condensation
between the acid chloride the amine at the interface.

23. References
1. Textbook of polymer science by Fred W. Bill
Meyer, JR.
2. Polymer science by V R Gowariker and
Sreedhar.
3. Controlled drug delivery by Joseph R.
Robinson & Vincent H. Lee
4. Controlled release of biologically active
agents by Richard W. Baker

24. Thank you