Classify the polymers on the basis of their physical properties with example from each class in organic chemistry
Answers
The word “Polymer” is derived from two Greek words, ‘Poly’ that means many (numerous) and ‘Mer’ which means units. In basic terms, a polymer is a long-chain molecule that is composed of a large number of repeating units of identical structure. These identical structures, we understand as a unit made up of two or more molecules, join together to form a long chain.
polymers
Simply stated, a polymer is a long-chain molecule that is composed of a large number of repeating units of identical structure. Those monomers can be simple — just an atom or two or three — or they might be complicated ring-shaped structures containing a dozen or more atoms.
Classification Of Polymers
Since Polymers are numerous in number with different behaviours and can be naturally found or synthetically created, they can be classified in various ways. The following below are some basic ways in which we classify polymers:
1] Classification Based on Source
The first classification of polymers is based on their source of origin, Let’s take a look.
(i) Natural polymers
The easiest way to classify polymers is their source of origin. Natural polymers are polymers which occur in nature and are existing in natural sources like plants and animals. Some common examples are Proteins (which are found in humans and animals alike), Cellulose and Starch (which are found in plants) or Rubber (which we harvest from the latex of a tropical plant ).
(ii) Synthetic polymers
Synthetic polymers are polymers which humans can artificially create/synthesize in a lab. These are commercially produced by industries for human necessities. Some commonly produced polymers which we use day to day are Polyethylene (a mass-produced plastic which we use in packaging) or Nylon Fibers (commonly used in our clothes, fishing nets etc.)
(iii) Semi-Synthetic polymers
Semi-Synthetic polymers are polymers obtained by making modification in natural polymers artificially in a lab. These polymers formed by chemical reaction (in a controlled environment) and are of commercial importance. Example: Vulcanized Rubber ( Sulphur is used in cross bonding the polymer chains found in natural rubber) Cellulose acetate (rayon) etc.
Classification of polymers based on their structure can be of three types:
(i) Linear polymers:
These polymers are similar in structure to a long straight chain which identical links connected to each other. The monomers in these are linked together to form a long chain. These polymers have high melting points and are of higher density. A common example of this is PVC (Poly-vinyl chloride). This polymer is largely used for making electric cables and pipes.
(ii) Branch chain polymers:
As the title describes, the structure of these polymers is like branches originating at random points from a single linear chain. Monomers join together to form a long straight chain with some branched chains of different lengths. As a result of these branches, the polymers are not closely packed together. They are of low density having low melting points. Low-density polyethene (LDPE) used in plastic bags and general purpose containers is a common example
(iii) Crosslinked or Network polymers:
In this type of polymers, monomers are linked together to form a three-dimensional network. The monomers contain strong covalent bonds as they are composed of bi-functional and tri-functional in nature. These polymers are brittle and hard. Ex:- Bakelite (used in electrical insulators), Melamine etc.
3] Based on Mode of Polymerisation
Polymerization is the process by which monomer molecules are reacted together in a chemical reaction to form a polymer chain (or three-dimensional networks). Based on the type of polymerization, polymers can be classified as:
i) Addition polymers:
These type of polymers are formed by the repeated addition of monomer molecules. The polymer is formed by polymerization of monomers with double or triple bonds (unsaturated compounds). Note, in this process, there is no elimination of small molecules like water or alcohol etc (no by-product of the process). Addition polymers always have their empirical formulas same as their monomers. Example: ethene n(CH2=CH2) to polyethene -(CH2-CH2)n-.
ii) Condensation polymers:
These polymers are formed by the combination of monomers, with the elimination of small molecules like water, alcohol etc. The monomers in these types of condensation reactions are bi-functional or tri-functional in nature. A common example is the polymerization of Hexamethylenediamine and adipic acid. to give Nylon – 66, where molecules of water are eliminated in the process.