Molecular mechanism of solvent-induced crystallization of syndiotactic polystyrene glass. 2. Detection of enhanced motion of the amorphous chains in the induction period of crystallization

Syndiotactic polystyrene (sPS) glassy sample crystallizes into the polymer-solvent complex of delta form with T(2)G(2) helical conformation when it is exposed to the atmosphere of organic solvent. This solvent-induced crystallization is observed at room temperature, much lower than the glass transition temperature of sPS. This experimental fact implied that the molecular motion of the amorphous chains should be enhanced more or less by absorption of solvent even below the glass transition temperature. This prediction could be confirmed experimentally by measuring the time-dependent change in the half-width and peak position of the infrared bands of the amorphous chains on the basis of such an idea that the half-width is larger and the vibrational frequency is lower as the molecular motion is accelerated to higher extent. In fact, the half-width was found to increase largely, and the peak position shifted toward lower frequency side when the solvent was supplied to the glassy sPS sample, indicating an enhancement of the amorphous chain motion by which the random coils were regularized to form short helical segments. As the time passed furthermore, the helical length was found to increase, and these long helices gathered together to form the crystalline lattice, as being observed in the remarkable increment of the crystalline peaks of the infrared and Raman bands as well as the X-ray diffraction intensity. The accelerating rate of molecular motion of the amorphous chain and the formation rate of regular helical chains were found to be dependent on the kind of solvent used in the experiment: chloroform, benzene, and toluene.