高于玻璃化温度T_g退火对无规聚甲基丙烯酸甲酯液-液转变的影响

Effects of Annealing Above Glass Transition Temperature T_g on the Liquid-liquid Transition of Atactic Poly(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 ll shifted to higher temperature with the decrease in transition intensity, on the contrary, when T a was over 443 K, T ll declined and transition intensity increased. When T a kept constant with the increase of t a, T ll and transition intensity varied as the results described above. Moreover, the variation extent of T ll 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 ll 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).