Effects of annealing above glass transition temperature Tg on the liquid-liquid transition of atactic polly(methyl methacrylate)

Effects of annealing temperature(T-a) and annealing time(t(a)) on the liquid-liquid transition and transition intensity of atactic poly(methyl methacrylate) were studied by means of differential scanning calorimetry. With the increase of T-a from 393 to 443 K, T-II shifted to higher temperature with the decrease in transition intensity, on the contrary, when T-a was over 443 K, T-II declined and transition intensity increased. When T-a kept constant with the increase of t(a), T-II and transition intensity varied as the results described above. Moreover, the variation extent of Tu and transition intensity increased with the increase of T-a, in other words, the time needed reaching the maximum extent of variation of the two parameters was decreased with the increase of T-a. The dependence of T-II and transition intensity on annealing conditions may be explained by the formation of local ordered structure, i.e, stereocomplex, during the annealing process by means of Van der Waals forces between isotacitic and syndiotactic segments of the same or different chains of atactic poly(methyl methacrylate).