CBSE Class 12 Chemistry Notes: Polymers – Copolymerisation

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:-

1. They have similar properties like alloying in mettalurgy.
2. Polystyrene is a good electrical insulator.
3. 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:-

1. It is used in manufacture of noses, gaskets.
2. 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:-

1. 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:-

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

It is used for:-

1. For stitching of wounds after operation.
2. 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]

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