Gce Model Questions Vol1 2018 Chemistry Question 27

Consider the free‑radical copolymerisation of monomer A (\(T_{gA}=100\) °C, \(M_A=100\) g mol⁻¹) and monomer B (\(T_{gB}=200\) °C, \(M_B=200\) g mol⁻¹). The feed mole fraction of A is \(x_A=0.30\). (a) Assuming the copolymer composition equals the feed (no composition drift), calculate the glass‑transition temperature \(T_g\) of the random copolymer using the Fox equation \(\frac{1}{T_g}=\frac{w_A}{T_{gA}}+\frac{w_B}{T_{gB}}\) (temperatures in K). (b) Given reactivity ratios \(r_A=0.8\) and \(r_B=1.2\), determine the instantaneous mole fraction of A in the polymer at low conversion using the Mayo-Lewis equation \(F_A=\frac{r_A x_A^2 + x_A x_B}{r_A x_A^2 + 2 x_A x_B + r_B x_B^2}\). Then recalculate \(T_g\) for the copolymer formed under these conditions.