Neco 2021 Chemistry Question 43

A sample of poly(vinyl chloride) (PVC) shows an intrinsic viscosity \([\eta]=0.85\) dL·g⁻¹ in a particular solvent at 25 °C. The Mark-Houwink parameters for PVC in this solvent are \(K=1.2\times10^{-3}\) dL·g⁻¹ and \(a=0.80\) (\([\eta]=K\,M^{a}\)).\n(a) Calculate the number‑average molecular weight \(M_{n}\) of the polymer.\n(b) When this polymer is blended with a plasticiser, the tensile strength of the blend falls linearly with plasticiser content. A 25 % (w/w) plasticiser blend shows a 30 % reduction in tensile strength relative to the pure polymer. Assuming the same linear relationship, estimate the percentage of the original tensile strength retained in a blend containing 15 % plasticiser.