2.1 INTRODUCTION

The word polymer is made from greek words, poly meaning many and meros meaning parts or units. It is defined as a high molecular weight compound formed by the combination of a large number of one or more types of molecules of low molecular weight. In other words polymers are giant molecules of high molecular weight, called macromolecules, which are built up by linking together large numbers of small molecules, called monomers, and the reaction by which the monomers combine to form polymers is known as polymerization. For example, if a simple molecule is x, then the molecule x _n, represented by the formula

is the polymer of x.

Polymers with a high degree of polymerization are called high polymers and those with low degree of polymerization are called oligo polymers. Macromolecules of biological significance, such as proteins, carbohydrates, etc., are called biopolymers. Silicates, silicones, etc. are termed as inorganic polymers.

2.2 CLASSIFICATION OF POLYMERS

Polymers can have different chemical structures, physical properties, mechanical behaviors, thermal characteristics, etc., and can be classified in different ways (see Figure 2.1). Some common classes of polymers based on their characteristics are:

1. Origin. Based on the origin, polymers are classified as:

   1. Natural Polymers. These are available in nature and include natural rubber, natural silk, cellulose, starch, proteins, etc.

   2. Semi-synthetic Polymers. These are chemically modified natural polymers such as hydrogenated, halogenated or hydrohalogenated natural...