Question

What are the methods of polymerization?

Answer 1

To determine the methods of polymerization, we first need to know what polymers are. A compound that is formed by the combination of several molecules called monomers and has a high molecular weight is known as polymers.

Complete answer:
The process of conversion of monomers (small units or simple molecules) into a polymer is known as polymerization.
There are two major methods of polymerization
1. Addition polymerization is also known as chain-growth polymerization
In chain-growth polymerization or addition polymerization, monomeric units are added to each other successively to form polymers. As the name suggests, it follows a chain-by-chain mechanism.
During the process of addition polymerization, the formation of active intermediate species like anions, cations, or free radicals takes place. The polymerization methods for these species are
A Radical polymerization
In radical polymerization, unsaturated compounds such as dienes or alkenes are used to form polymers. The monomer alkene is converted into a radical using a radical initiator. The monomer reacts with this radical form and this process keeps on growing the chain and the chain is formed endlessly.
B. Cationic polymerization
In cationic polymerization, an alkene is converted into a cation upon the addition of an electrophile initiator like $B{{F}_{3}}$ or $A{{l}_{3}}C{{l}_{3}}$. This cation forms reacts with another monomer to form a cation and the process continues endlessly.
C. Anionic polymerization
In anionic polymerization, an alkene is converted into an anion i.e., a propagating site upon the addition of a nucleophile initiator. Styrene, acrylonitrile, vinyl chloride, etc are produced using this process.
2. Condensation polymerization is also known as step-growth polymerization
In condensation polymerization, a series of independent reactions take place through intermolecular condensation. This reaction takes place in monomer molecules that have multiple functional groups that are either dissimilar or similar.
In every reaction, there is a condensation process that involves the release of simple molecules like $N{{H}_{3}}$, ${{H}_{2}}O$, HCl, etc.
Polymers like nylon, bakelite, and dacron are formed using condensation polymerization.

Note:
It should be noted that during anionic addition polymerization, an alkene having a substituent which is electron-withdrawing is attached to is used along with a strong nucleophile since alkenes are electron-rich species and the attack of nucleophile isn't easy.