Copolymerisation or Heteropolymerisation Preparation and Properties
→ Copolymerisation is a polymerisation reaction in which a mixture of more than one monomeric species is allowed to polymerise and form a copolymer. The copolymer can be made not only by chain growth polymerisation but by step growth polymerisation also. It contains multiple unit of each monomer used in the same polymeric chain. It is generally represented as:
Styrene butadiene rubber is formed by addition co-polymerisation.
→ Nylon 6,6 is formed by condensation copolyrnerisation because it contains two types of monomers Adipic acid and hexamethylene diamine. Thus, polymers formed by condensation copolymerisation are called copolymers.
Types of copolymers
→ In Copolymers. different monomer units are joined in different types. On the basis of arrangement of monomer units, polymers are of four types
→ Random Copolymers : In these polymers, there is no regular arrangement of monomer units. These can be represented as:
→ Alternating Copolyiner : In these polymers. monomer units are joined in alternating manner. These can be represented as:
→ Block Copolymers : In these polymers. first a block is formed by one type of monomer units, and second block is formed by another monomer units. This process continues. This can be represented as:
→ Graft Copolymers : In this, one monomer units combine to form a chain then another monomer units adds as branches. It can be represented as:
Uses of Copolymerisotion
Copolymers can be used commercially by modifying their properties as:
→ Nylon 6,6 which is a polymer of Hexamethylene Diamine and Adipic acid is formed by condensation polymersation but it has low melting point and and a hard crystalline solid. If Terepthalic acid is added to it by copolymerisation, then crystalline property and melting point both will increase.
→ The copolymer formed by adding 20-30% Acrylonit rile to Styrene is resistant to impact and Hydrocarbons.
→ Copolymer of Styrene and Butadiene is synthetic rubber.
→ Homopolymer is formed by polymerisation of same monomer units and a copolymer shows properties of two homopolymers. Thus, copolymerisation is a useful method for increasing commercial applications of polymers. In this, properties of more than one homopolymers can be mixed.