POLYMORPHISM IN MELT CRYSTALLIZED SYNDIOTACTIC POLYSTYRENE SAMPLES

Both the crystalline forms containing zigzag planar conformations (pure or mixed) can be obtained by melt crystallization of syndiotactic polystyrene. Some of the factors that influence the polymorphic behavior in samples crystallized on cooling from the melt are described: the cooling rate from the melt, the crystalline form of the starting material, the maximum temperature of the melt, the time of residence in the melt at that temperature, and, in some cases, also the heating rate to reach melting. A possible interpretation of the observed polymorphic behavior in melt crystallizations for moderate cooling rates is that when a memory of α-form crystals remains in the melt, the acquisition of the α form is favored, otherwise the β form is obtained. The formation of the a form, also by quenching from the melt or by annealing from the amorphous phase, could be a kinetically controlled process. © 1990, American Chemical Society. All rights reserved.