Copolymerization, Chemistry tutorial

Introduction

When a polymer is made via bonding only one kind of tiny molecule or monomer mutually, it is said a homopolymer. When 2 dissimilar kinds of monomers are connected in the similar polymer chain, the polymer is said a copolymer.

Copolymerization might be described as the simultaneous polymerization of two or more monomers to form a polymer enclosing both or all the monomers. The product is termed a copolymer. There is a definite reaction between the monomers, and the procedure can be symbolized as 

            A + B                        ~A-A-B-B-B-A-A-B-B-A~

Simultaneous polymerization of more than 2 monomers is generally termed to as multicomponent copolymerization through the products termed terpolymer, quadripolymer, and so on.

Types of copolymers   

The synthesis of macromolecules composed of more than one monomeric repeating unit has been explored as a means of controlling the properties of the resulting material. In this respect, it is useful to distinguish several ways in that different monomeric units might be incorporated in a polymeric molecule. Assume that two monomers will be said A and B, instances comprise:

(a) Random copolymers - Here the monomeric units are distributed arbitrarily, and sometimes unevenly, in the polymer chain:   

                             ~A-B-B-A-A-A-B-A-A-B-B-B-A-B-A-A-B-A~       

(b)  Alternating copolymers - The monomeric units are distributed in a regular alternating fashion, through nearly equimolar amount of each in the chain:

               ~A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B~

(c) Block copolymers - Instead of a blended distribution of monomeric units, a long sequence or blocks of one monomer is joined to a block of the 2nd monomer:

A-A-A-A-A-B-B-B-B-B-B-A-A-A-A-A-A-B-B-B-B~

(d) Graft copolymers - Here the blocks of one monomer are grafted or connected to the backbone of another monomer as branches. 

Block and Graft copolymers are of particular interest. Their most interesting traits are that they exhibit many properties connected through each homopolymer. Therefore they demonstrate two transition temperatures and if both polymer kinds are crystalline, two crystalline melting points are examined. Random and alternating copolymers on the other hand, have traits somewhere between those of the 2 homopolymers. 

Benefits of copolymerization 

Copolymerization provides a means of exercising control over polymer properties - It progress tensile strength, impact strength (toughness), ductility (elongation of break), flexibility, chemical resistance, and permeability to water vapour, gas permeability, surface modification, and ease of processing. Instances -

  • Polystyrene is a brittle thermoplastic with poor impact strength, poor solvent resistance and low softening point. However, copolymerization of styrene with acrylonitrile yields a transparent product through better contact strength, increased solvent resistance and higher softening point.
  • Copolymerization through butadiene yields elastomers while copolymerization of 3 monomers, styrene, acrylonitrile and butadiene a product in that all the 3 properties are all together developed (a true engineering plastic).

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