Neco 2017 Chemistry Question 35

A step‑growth polymer is formed by reacting monomer A (molar mass \(M_A = 100\ \text{g mol}^{-1}\)) with monomer B (molar mass \(M_B = 150\ \text{g mol}^{-1}\)) in an exact 1:1 molar ratio. After polymerisation the number‑average degree of polymerisation is measured to be \(DP_n = 250\). (a) Calculate the number‑average molecular weight \(M_n\) of the polymer. (b) The polymer is then subjected to a random chemical degradation that cleaves 5 % of the polymer bonds uniformly along the chains. Estimate the new average degree of polymerisation after degradation. (c) Assuming the tensile strength of a polymer is directly proportional to its degree of polymerisation, discuss qualitatively how the degradation will affect the tensile strength.