Question

A random poly(isobutylene-isoprene) copolymer has a number-average molecular weight of 202000 g/mol and a degree of polymerization of 3030. Compute the fraction of (a) isobutylene and (b) isoprene repeat units in this copolymer.

Answer 1

The fraction of isobutylene repeat units in the copolymer is 1, while the fraction of isoprene repeat units is 0.

Step-by-step explanation:

In order to calculate the fraction of isobutylene and isoprene repeat units in the copolymer, we need to consider the composition of the copolymer and the degree of polymerization.

(a) To calculate the fraction of isobutylene repeat units, we divide the number of isobutylene repeat units by the total number of repeat units:

Fraction of isobutylene repeat units = (number of isobutylene repeat units) / (total number of repeat units)

= (number of isobutylene repeat units) / (number of isobutylene repeat units + number of isoprene repeat units)

Substituting the values:

Fraction of isobutylene repeat units = (3030) / (3030 + 0)

= 1

Therefore, the fraction of isobutylene repeat units in the copolymer is 1.

(b) Similarly, to calculate the fraction of isoprene repeat units, we divide the number of isoprene repeat units by the total number of repeat units:

Fraction of isoprene repeat units = (number of isoprene repeat units) / (total number of repeat units)

= (number of isoprene repeat units) / (number of isobutylene repeat units + number of isoprene repeat units)

Substituting the values:

Fraction of isoprene repeat units = (0) / (3030 + 0)

= 0

Therefore, the fraction of isoprene repeat units in the copolymer is 0.