Conformational Change and Orientation Fluctuations Prior to the Crystallization of Syndiotactic Polystyrene

Abstract

Aiming to clarify the mechanism of crystal nucleation of polymers, we have made a quantitative investigation about the conformational change of syndiotactic polystyrene (sPS) during the induction period (ca. 30 min) when crystallized at 120 °C, 25 K above the glass transition temperature Tg = 95 °C, from the glassy state, i.e., for the so-called glass crystallization by time-resolved Fourier transform infrared (FT−IR) spectroscopy. It was found that even in the induction period, the absorbance of trans conformation bands begins to increase and it continues to increase not only through the induction period but also after crystallization. This suggests that the length of rodlike segments consisting of trans sequences starts to increase in the induction period. In this connection, Doi's theory on the isotropic-to-nematic transition of polymer liquid crystals has predicted that the extension of these segments triggers the orientation fluctuations of the rod segments because the increase of their excluded volumes makes the system unstable. To confirm such orientation fluctuations directly, we have also carried out time-resolved depolarized-light-scattering (DPLS) measurements. With the temperature jump to 120 °C from the glass, orientation fluctuations actually begin to occur and increase exponentially with time in the induction period. These results also support a previous proposal that a spinodal-decomposition-type microphase separation due to orientation fluctuations occurs in the induction period.