Copolymerization

Despite significant advances in understanding single monomer polymerization, a comprehensive study of copolymerization has been impeded. 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. However, the phrases “terpolymerization” and “multicomponent polymerization” are widely used to refer to the polymerization of three monomers and three or more monomers, respectively.

Copolymerization

Many monomers form a chain-like structure called ‘Polymers’. These polymers have repeating subunits. The name of the process through which polymers are formed is called Polymerization. In such a polymer if the monomers are from different species then it is called a copolymer. These copolymers are formed by a process called Copolymerization.

Definition of Copolymerization

Copolymerization is a process in which two or more types of different monomers polymerize to form a Copolymer. A copolymer is different from a homomer. In homomers, only the same type of monomer polymerizes rather than in a copolymer different types of monomers polymerize. 

Sequence of homomer

A – monomeric subunit

Examples of homomer

Poly-ethylene or -(-CH2CH-)n–

Sequence of copolymer

A – monomer 1

B – monomer 2

Examples of copolymer

nitrile rubber, acrylonitrile butadiene styrene, and polyethylene-vinyl acetate (PEVA).

Types Of Copolymerization

Copolymers can be broadly classified into two categories. They are linear polymers and branched polymers. 

Structure of a linear polymer

Structure of a branched polymer

Linear Polymers

A linear chain, or a single backbone with no branches, is the most basic polymer architecture. A linear polymer is a long chain of carbon-carbon bonds in which the remaining two valence bonds are primarily coupled to hydrogen or a minor hydrocarbon component. The linear copolymers are further classified into four types based on the order of different monomers in the linear chain of polymers. The four classifications are:

1. Block Copolymers
2. Statistical Copolymer
3. Alternating Copolymers
4. Periodic Copolymers
5. Gradient and Stereoblock Copolymers

Block Copolymers

A block copolymer is a polymer made up of molecules arranged in a linear pattern, with a block defined as a piece of a polymer molecule in which the monomeric units have at least one constitutional or configurational trait that the surrounding portions do not. The resulting single-chain macromolecule is called a block copolymer when more than one homopolymer unit is joined together by covalent connections. A junction block is an intermediary unit that connects the two homopolymer chains. A diblock copolymer is made up of two homopolymer blocks, whereas a triblock copolymer is made up of three homopolymer blocks. The constitutional property of a block copolymer is that each of the blocks is made up of units produced from a specific monomer species. At nanoscopic length scales, block copolymers can create a variety of ordered phases. When block copolymers are coupled with rigid templates of various shapes and sizes, limiting environments severely limit the morphologies that the block copolymers can produce.

Illustration of a Block Copolymer

Example of Block Copolymer

PS-b-PMMA or polystyrene-b-poly(methyl methacrylate) (where b = block)

Statistical Copolymer

In statistical copolymers, the sequential distribution of monomeric units follows well-known statistical laws. For example, the monomer sequence distribution could follow Markovian statistics of zeroth (Bernoullian), first, second, or higher order. The entire polymer is known as a random polymer if the mole fraction of a monomer is equal to the chance of finding a residue of that monomer at any point in the chain. The free-radical polymerization process is commonly used to make these polymers. The elementary processes that lead to the production of a statistical sequence of monomeric units may not always proceed with equal probability kinematically. These processes can result in a variety of sequence distributions, including those in which monomeric unit organization tends toward alternation, clustering of like units, or no ordering tendency at all.

Illustration of a Statistical Copolymer

Example of Statistical Copolymer

Styrene and butadiene copolymerized rubber

Alternating Copolymers

A copolymer with two kinds of monomeric units dispersed in the alternating sequence is known as an alternating copolymer. As a result, the arrangement -ABABABAB- or (AB)n denotes an alternating copolymer. (A-alt-B) is the alternate sequence arrangement of monomeric units (A-alt-B), and poly is the alternating copolymer that corresponds to it (A-alt-B). Alternating sequence arrangements can result in constitutionally regular structures, which can be termed using the structure-based nomenclature for regular single-strand organic polymers in those circumstances.

Illustration of an Alternating Copolymer

Example of Alternating Copolymer

Nylon 6, poly[styrene-alt-(maleic anhydride)]

Periodic Copolymers

The monomers are organized in a single chain in these polymers, which has a repeating sequence. CRP methods can also be used to make periodic and alternating copolymers. They can be made from comonomers with a natural inclination to alternate, such as copolymerization reactions involving a strong electron accepting monomers like maleic anhydride or N-substituted maleimides and an electron-donating monomer like styrene.

Illustration of a Periodic Copolymer

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Gradient and Stereoblock Copolymers

Gradient copolymers are single-chain copolymers in which the monomer content gradually changes throughout the main chain. A stereoblock copolymer is a macromolecule in which the tacticity of the monomers varies with different blocks or units of the polymer. Stereoblock polymers are made by making sudden modifications to the chain at specific points.

Branched Copolymer

A branched copolymer is a polymer in which the monomers are arranged in a branching structure, as the name suggests. Sidechains or branches sprout out from the main chain in branched polymers. The same repeating units make up the side chains and branches as the main polymer chains. Side reactions during polymerization cause the branches. Branching is more likely in monomers with two or more end groups. The different types of branched polymers are: 

• grafted copolymer

1. Comb copolymer
2. Brush copolymer
3. Star-shaped copolymer

Grafted copolymer

Graft copolymers are branched copolymers with different-structured main chains and side chains. Graft copolymers have molecular architectures that are branched. A seemingly linear main chain (the backbone) has polymeric side chains (grafts) of various chemical types connected to it, which are arranged randomly in most situations.

Illustration of Graft Copolymer

Comb copolymer

Comb-shaped copolymers are complex polymers with a primary chain (or backbone) onto which chemically distinct side chains are grafted. Cement and concrete, limestone, silica, gypsum, barium titanate, and magnesia have all used comb-shaped copolymers with an anionic backbone as dispersants to stabilize diverse suspensions. A comb polymer, according to the IUPAC gold book, is a polymer made up of comb macromolecules. In other words, it is made up of side chains on the same side of the backbone, resulting in a comb-like polymer.

Illustration of Comb Copolymer

Brush copolymer

The backbone of this type of polymer is replaced with side chains from various points, giving it the appearance of a brush. These polymers have a high density.

Illustration of Brush Copolymer

Star-shaped copolymer

Star polymers are three-dimensional hyperbranched polymers with linear arms of the same or differing molecular weight radiating from a central core. Arm-first or core-first approaches can be used to make star polymers.

Illustration of star-shaped copolymer

Copolymerization is a technique for altering the properties of manufactured plastics to satisfy specific requirements, such as lowering crystallinity, changing the glass transition temperature, controlling wetting qualities, or increasing solubility. This procedure, known as rubber toughening, improves mechanical qualities. When a rigid matrix is impacted, elastomeric phases within the matrix operate as crack arrestors, increasing the energy absorption. A common example is acrylonitrile butadiene styrene.

Conclusion:

A polymer is a giant molecule containing a high number of repeating units. Polymers can be grouped as linear polymers and branched polymers depending on their structures. The main difference between branched polymer and linear polymer is that branched polymers have a branched structure whereas linear polymers have a linear structure.A linear polymer is a macromolecule made out of many monomer units arranged in a straight line. A linear polymer consists of a single continuous chain of repeating units.

A branched polymer is a macromolecule made from the polymerization of monomers and has a branched structure.