Brief Notes on Copolymerization

A polymer is a natural or manmade material that is made up of very big molecules. Many of the components found in living creatures are polymers, such as proteins, cellulose, and nucleic acids. They also serve as the foundation for minerals like diamond, quartz, and feldspar, as well as man-made materials like concrete, glass, paper, plastics, and rubbers.

Copolymerization provides versatility in terms of monomer options and a wide range of polymeric products, but it also introduces composition drift, which must be avoided or used in a regulated manner for certain structure-property correlations.

What are Co-polymers?

A copolymer is a polymer made up of two or more separate repeating units known as “monomers.” It creates high molecular weight molecules by chemical reactions or monomer polymerization. It’s used to make plastics, tyres, and tubes, among other things. Copolymer differs from homopolymer in that it comprises at least two types of monomers, whereas homopolymer has just one.

Copolymerization can alter the characteristics of polymers to fulfill specific requirements. Corrosion inhibitors are also made from copolymers. They aid in the improvement of plastic materials’ mechanical characteristics.

What is Co-Polymerization?

Metals are frequently alloyed to improve their qualities, and while many polymers are relatively pure today (e.g., polystyrene, nylon), a growing number are combinations of two or more polymers. One rationale for this, like with metals, is to broaden the variety of characteristics. However, the main practical issue is that homopolymers mix poorly, and even when blends are feasible, such as in some thermoplastics, phase separation can occur quickly.

Copolymerization, or the polymerization of a combination of monomers, is a common solution to this problem.

Because of the possibilities of branching, structural isomerism within a single monomer, and the way the various repeat units may be joined together, it provides a significantly wider spectrum of structures than combining homopolymers. Furthermore, composition and, of course, molecular mass can be altered to create the required balance of attributes in the final product.

Types of Co-polymers

A copolymer includes at least two types of monomers, and the copolymers are divided into different categories based on how these monomers are placed in the chain. There are two fundamental types:

1. Copolymers with a linear structure
2. Copolymers with Branches

The linear copolymers, which have a single main chain, are divided into three types: alternating, statistical, and block copolymers. Grafted and star-shaped copolymers are two types of branched copolymers.

• Block Copolymer- The resultant polymeric chain is called a Block copolymer when two or more homopolymer chains are linked by covalent connections. A junction block is an intermediary unit where they connect. These copolymers might be diblock or triblock.

For example-  1) SBS rubber is a block copolymer that is used to create automotive tyres (acrylonitrile butadiene styrene). 

2) Polystyrene and polybutadiene are the building ingredients of SBS rubber (Styrene Butadiene Styrene). Copolymers include nitrile and ethylene-vinyl acetate.

• Statistical Copolymer- A statistical copolymer is one in which the sequencing of monomeric units follows a statistical rule. Furthermore, a random polymer is defined as one in which the probability of finding a given monomer at a specific location in a chain is equal to its mole fraction in the chain.

For example- rubber is made of styrene-butadiene copolymers, styrene-acrylic resins, and so on.

• Alternating Copolymer- A copolymer with two kinds of monomeric units dispersed in an alternating sequence is known as an alternating copolymer.

For example- Nylon 6,6. The monomers A and B have the following generic formula: -(-A-B-)n- 

• Grafted Copolymer- Special branched copolymers with structurally distinct side chains from the main chain. The main chain can be covalently connected to one or more side chains in this configuration.

For example- Polystyrene chains can be grafted into polybutadiene.

Importance of Co-Polymerization

Styrene homopolymer makes up only approximately a third of the total. Polystyrene is a brittle, low-impact plastic with low solvent resistance. Polystyrene’s use is substantially enhanced through copolymerization and mixing. Styrene copolymers and blends of copolymers can be used as elastomers as well as plastics. Styrene copolymerization with acrylonitrile improves impact and solvent resistance, whereas copolymerization with 1,3-butadiene improves elastomeric characteristics. Styrene, acrylonitrile, and 1,3-butadiene blends improve all three qualities at the same time. Copolymerization is used in these and other technical applications.

Conclusion

Copolymerization is the chemical combination of copolymers. Copolymers come in a variety of kinds, and it’s critical to grasp their features in order to fully comprehend the copolymerization procedure. Copolymers with styrene as a comonomer include thermoplastics [e.g., poly(styrene-co-acrylonitrile), SAN] and elastomers [poly(styrene-co-butadiene), SBR, and poly(styrene-block butadiene-block styrene), SBS].