Polymer is a Greek word that means many parts. A polymer, also known as a macromolecule, is a large molecule of numerous subunits. Polymers are available in almost every area, from DNA to polypropylene. Natural polymers are found naturally in plants and animals, while synthetic polymers are produced artificially. Polymers contain a variety of chemical or physical qualities that enable compounds to be used in daily life.
Polymerization is a chemical reaction in which many monomer molecules combine to produce a polymer. A polymerization can yield macromolecules with a linear or branching structure. They can also take the form of a three-dimensional, complicated network. Polymerization reactions are divided into various types, the most famous of which are chain-growth polymerization, condensation polymerization, and step-growth polymerization.
Initiation, propagation, and termination are the three stages of polymerization. In terms of reaction mechanisms, polymerization is achieved by two methods, which are the
- Chain-growth mechanism
- Step-growth mechanism.
Chain Growth Polymerization
The monomer molecules are combined to form a long chain in chain-growth polymerization. The monomers may be of the same type or a different type. Alkadienes, Alkenes, and their derivatives are used. Chain lengthening happens in this phase of the production of ionic species or free radicals.
Step Growth Polymerization
Polymers are synthesised by reacting between the functional groups of simple monomer units in step-growth polymerization.
- Condensation polymerization is an example of step-growth polymerization, in which a water molecule is evolved as the chain lengthens. To generate a longer-length molecule, every step in step-growth may consist of a mixture of two polymers of differing or equal lengths.
- The reaction takes a long time to complete, and the molecule mass increases at a relatively slow rate.
Classification of Polymers
Polymers are categorised into three groups based on their structure: cross-linked polymer, linear polymers, and branched-chain polymers.
|Cross-linked polymers have cross-linkages between them. They’re usually made up of bi or tri-functional monomers.Example: Melamine
|A linear polymer is made up of monomers with long, straight chains.Example: PVC
|Linear polymers with some branches are known as branched polymers.Example: LDPE(Low-density polyethene)
Polymers are divided into three types based on their origin: natural polymer, semi-synthetic polymer, and synthetic polymer.
|Polymers that occur spontaneously in plants and animals are known as natural polymers.Example: Starch
|Natural rubber is treated with synthetic polymers. That is, natural rubbers are chemically modified to make them semi-synthetic.Example: Cellulose nitrate
|The term synthetic polymer refers to totally man-made polymers.Example: Nylon 66
Preparation of Polymer
Synthetic polymer refers to polymers that are created in laboratories. Scientists and engineers from petroleum oil create synthetic polymers. Polythene, nylon, polyester, epoxy, and teflon are instances of synthetic materials which can be prepared using particular catalyst and conditions.
|LDPE (Low-density polyethene)
|Temperature – 350 to 520KPressure – 1000 to 2000 atmospheresCatalyst – Dioxygen or peroxide initiator
|HDPE (High-Density Polyethene)
|Temperature – 343 KPressure – 3 to 4 atmospheresCatalyst – Triethyl aluminium and titanium tetrachloride.
|Free radicalHigh pressure