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]
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CBSE Class 12 Chemistry Polymers All Topic Notes CBSE Class 12 Chemistry All Chapters Notes
