Polymer

Polymer: “Polymers having long chain macromolecules, which are built up by the linking together of a large number of small molecules, called monomer”. “The polymer (poly- many; mer-unit or parts) is a high molecular weight compound, formed by the combination of small molecules of low molecular weight”.

                                                OR

Polymers are a large class of materials consisting of many small molecules (called monomers) that can be linked together to form long chains, thus they are known as macromolecules

                                                OR

The chemical approach assumed that polymer (poly- many; mer-unit or parts) is a high molecular weight compound, formed by the combination of a large number of one or more types of molecule of low molecular weight.

Basic Terms of Polymers

Polymerization: Polymers are giant molecules, called macromolecules, which are built up by the linking together of a large number of small molecules, called monomers and the reaction by which monomers combine to form polymers is known as polymerization

Degree of Polymerization (DP): The numbers of repeating unit present in it call degree of polymerization (DP).

Addition Polymerization: When molecules just add on to form the polymer, the process is called addition polymerization. The molecular Weight is just multiple of the molecular weight of the monomer.

Condensation Polymerization: When, however, molecules do not just add on but also undergo some reaction in forming the polymer, the process is called condensation polymerisation

The molecular weight of polymer is lesser by the weight of simple molecules eliminated during the condensation process

The condensation takes place between the two reactive functional groups, like the carbonyl group (of an acid) and hydroxyl group (of an alcohol) to form polyesters.

Polymer Material Properties Depends on

1. Degree of Polymerization

2. Molecular Weight of the Polymer

3. Molecular Weight Distribution

4. Glass Transition Temperature

5. Percentage of Crystallinity

6. Percentage of Amorphous Content in the Polymer

7. Structure and Distribution of Chain Branching

A polymer consist of identical monomers or monomers of different chemical structure and accordingly they are called homopolymer and copolymers respectively. If the main chain is made up of same species of atoms, the polymer is called homochain polymer Graft copolymer are branched structures in which the monomer segments on the branches and backbone differ

The monomeric unit in a polymer may be present in a linear, branched or cross-linked (three dimensional) structure.

TACTICITY

1. The head to tail configuration in which the functional groups are all on the same side of the chain, is called isotactic polymers.

2. If the arrangements of functional groups are at random around the main, it is called atactic polymers e.g. polypropylene.

3. If the arrangements of side groups is in alternating fashion, it is called synditactic polymers e.g. gutta percha.