Introduction

The performance properties of fibres are determined by the structure of the fibres, which in turn depends on the processing technique, and chemical structure and physical properties of polymers. (e.g. molecular wt / molecular weight distribution, side reactions, thermal stability, chemical nature etc.) The key properties of polymers influencing fibre formation and properties are:

a) Chemical structure and properties

b) Mol wt and distribution

c) Defects in linear chain structure

d) Impurities or side reaction products

In this chapter, some important aspects of preparation of fibre forming polymers, especially synthesis and related problems are considered. The main reactions used in the preparation of polymers, with their respective mechanisms, kinetics, catalysis and side reactions, are discussed. The emphasis is more on the basic synthesis chemistry of fibre forming polymers rather than the production technology. The detailed production technology and commercial aspects of fibre forming polymers is available in various books and reviews.

Types of Polymerizations

Polymers are macromolecules built up by linking up of large number of smaller molecules termed as monomers. Two main routes are used for synthesis of these macromolecules:

Step and chain growth polymerization differ in the nature of starting monomer units and the manner in which polymer molecular size depends on the extent of conversion.

What is step growth polymerization?

Step growth polymerizations generally proceed by condensation reaction between the functional groups of reactant molecules and elimination of small molecular weight molecules like water. In condensation reactions each of the two reactants can react at one point. Therefore, in monofunctional reactants, once this reaction has taken place the product is incapable of taking part in any further reactions as shown in equation [1-3]. Now, if the reactants capable of reacting at two sites are used the linear polymers suitable for fibre forming can form. In synthesis of polymers a minimum functionality of two is essential.

What is chain growth polymerization?

In chain growth polymerization the situation is quite different; the reactive double bond of the monomer is activated and opened up to form new bonds as shown in table 1.1. The chain polymerization is characterized by three steps: the initiation, the growth reaction and the termination reaction.