Question

Q2

(a) Explain the effect of each of the following changes on the molar mass of a polymer formed by radical polymerisation, assuming everything else is kept constant as much as possible:

(i) Doubling the initiator concentration

(ii) Reducing the monomer concentration by a factor of five

(iii) Adding a chain transfer agent

Answer 1

A. As the concentration of initiator increase, the no.of radicals doubles . As a result more no.of radicals of monomers start reacting. Even from the rate of polymerization equation, rate is directly proportional to the square root of initiator concentration and monomer concentration. So on doubling initiator concentration, rate of polymerization increases but molecular weight decreases.

B. If the concentration of monomers is decreased, the scope for chain propagation increases. Again using the same equation of rate of polymerization, the decrease in concentration of monomers by 5 time leads to a decrease in rate of polymerization but an increase in molar weight of polymer.

C. Chain Transfer agent transfers the activity of a growing polymer chain to another molecule . Chain Transfer reaction reduce the average molar weight of the resulting polymer.