CBSE Class 12 Chemistry Notes: Polymers

Copolymerisation:-when two or more different monomers are allowed to polymeric together the product formed is called a polymer and the process is called copolymerisation.

Example:-

Properties of copolymers:-

They have similar properties like alloying in mettalurgy.
Polystyrene is a good electrical insulator.
Buna – S have very fough, it possess very high abrasion resistance

Rubbers:-

(i) Natural rubber:-natural rubber has remarkable elasticity and it undergoes long range reversible extensions.

It is manufactured from latex-latex is obtained from bark trees.

Structure:-chemically natural rubber is a linear 1,4-addition polymer of isoprene (2-methyl-1, 3-Butadiene)

Vulcanized Rubber:-Natural rubber is very soft and brisky. It has high water absorption capacity and low tensile strength.

Its properties can be improved by a process called vulcanization. It is consist of heating raw rubber with sulphur at 373-415 K to increase rate of reaction zinc oxide is added.
During vulcanization sulphur bridges are or cross links between polymer chains are introduced either at their reactive allylic position or at double bond site.
Thus due to vulcanization rubber becomes hard and stronger and remove tackiness of natural rubber.

Synthetic rubbers:-

These may be defined as vuclcanizablerubber like polymers which is capable of getting stretched twice to its length.

1. Neoprene:-it is polymer of chloroprene (2-chloro,-1,-chloro,-1,3-butatiene)

Uses:-

It is used in manufacture of noses, gaskets.
It is used as an insulator and for making conveyor belts and printing rollers.

2. Buna-N:-it is arubber obtained by copolymerisation of 1,3-butadiene and acrylonitrile in presence of peroxide catalyst.

Uses:-

it is resistant to the action of petrol, lubricating oils and organic solvents, it is used for making oil seals, hoses and tank linings.

3. Thiokol:– it is prepared by copolymerisation of 1,2-dichloroethane with sodium tetra sulphide [Na2SO4] in presence of Mg(OH)2

Molecular mass of polymers:-

The properties of polymers depends largely upon their molecular mass, size and structure.

Biodegradable polymers:-The biopolymers which disintegrates by themselves in biological systems during a certain period of time by enzymatic hydrolysis and to some extent by oxidation are called biodegradable polymers.

(i) Poly-B-hydroxybutyrate-CO-B-hydroxyvalerate(PHBV): it is a copolymer of 3-hydronypentanoic acid in which monomer unit are connected by the ester linkage.

Uses:-

It is used in speciality packaging orthopaedic devices and in controlled drug release.
Poly(glycolic acid) (lactic acid):-This copolymer is called dentron.

It is used for:-

For stitching of wounds after operation.
It is used for the body securing purposes.

(ii) Nylon-2-Nylon-6:-it is an alternating polyamide glycine [containing two carbon atoms] and amionocaproicacid and 6–aminohexanioc acid [containing six carbon atoms]