Question

In a step-growth polymerization where “A” reacts with “B” forming “AB”, describe what happens when the ratio of reactants “A” and “B” is not 1:1.

Answer 1

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. 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. in case of ratio of reactants “A” and “B” is not 1:1, in such cases the polymerization reaction occurs via step growth manner till the one of the reactant (which exist in less concentration) should completly consumes.