Copolymerization

The type of monomers used and their structural distribution in the chain dictate a copolymer’s properties. It’s called copolymerization, when monomers are polymerised together to form copolymers. When two different monomer types are copolymerized together to form a polymer, the result is a bipolymer.

Terpolymers and quaterpolymers have three and four monomers, respectively.

Examples of Copolymers 

Copolymerization of 1,3-butadiene and styrene yields the Butadiene-Styrene copolymer.

 It’s a durable synthetic rubber substitute found in various products, including motor tyres, floor tiles, cable insulation, and footwear components. Hexamethylenediamine/adipic acid copolymerised with nylon 6-6 to form nylon 6-6.

Two common copolymers used in tiles, tyres, and cable insulation are butadiene-styrene (BST).

Created by combining the polymers 1, 3-butadiene, and styrene.

Types of Copolymers

Copolymers are available in a wide range of shapes and sizes.

1. Linear Copolymers

Linear copolymers are available in a wide range of forms and sizes.

There are several varieties of linear copolymers, including alternating and statistical copolymers. This classification is based on the arrangement of monomers in the main chain.

2. Block Copolymers

A block copolymer is a single-chain macromolecule formed when covalent connections join more than one homopolymer unit.

A junction block joins two homopolymer chains together.

A diblock copolymer has two homopolymer blocks, while a triblock copolymer has three homopolymer blocks.

The polymer acrylonitrile butadiene styrene, more often known as SBS rubber, is an example of this type of material.

3. Statistical Copolymers

Statistical copolymers are polymers made up of two or more monomers arranged in a statistically determined sequence.

It is claimed that a polymer is random if the mole fraction of a monomer equals the probability of finding a residue of that monomer at any position along the chain of the chain.

The free-radical polymerisation process is commonly used to produce these polymers.

Rubber manufactured from styrene and butadiene copolymers is known as a statistical polymer.

4. Alternating Copolymers

The primary chain of an alternating copolymer is composed of alternating monomers.

(-A-B-)n is the generic formula for an alternating copolymer composed of monomers A and B.

Hexamethylenediamine and adipic acid units alternate in the alternating copolymer Nylon 6,6.

5. Periodic Copolymer

The monomers are arranged in a single chain with a repeating sequence in these polymers. 

6. Gradient and Stereoblock Copolymers

Gradient copolymers are single-chain copolymers in which the monomer composition of the main chain varies with time. A stereo block copolymer is a macromolecule in which the tacticity of the monomers varies according to the polymer’s blocks or units.

 7. Branched Copolymer 

As the name implies, a branched copolymer is a polymer in which the monomers are arranged in a branching form. Branched copolymers include star, comb, grafted, and brush copolymers.

In a star copolymer, several polymeric chains are linked to the same central core.

The diagram above shows the architecture of many different types of star-shaped copolymers. They are made up of a multifunctional core that is coupled to three or more polymer chains.

8. Graft Copolymer

Graft copolymers are branched copolymers with main chains and side chains with various structures.  

Importance of copolymerization 

• Copolymerization allows for the development of a practically unlimited range of polymers, and it is frequently used in commercial applications of polymeric materials to obtain a better balance of properties
• Copolymers can be made using chain growth and step-growth condensation polymerization processes
• Only about a third of the total is made up of styrene homopolymer.
• Polystyrene is a brittle, low-impact, low-solvent-resistance material. Copolymerization and mixing significantly improve the utilisation of polystyrene. Styrene copolymers and blends of copolymers are useful as elastomers
• Impact and solvent resistance is improved by copolymerization styrene with acrylonitrile, but elastomeric properties are improved by copolymerization with 1,3-butadiene
• Blends of styrene, acrylonitrile, and 1,3-butadiene increase all three properties at once.

Conclusion

Copolymerization is a process of chemically combing the copolymers. Copolymers are of different types and it’s really important to understand the properties of copolymers to make a clear understanding of the mechanism of copolymerization. Thermoplastics [e.g., poly(styrene-co acrylonitrile), SAN] and elastomers [poly(styrene-co-butadiene), SBR, and poly(styrene-block butadiene-block styrene), SBS] are examples of copolymers having styrene as a comonomer.