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The phase structure of crystalline isotactic polystyrene (iPS) has been investigated with temperature-modulated differential scanning calorimetry (TMDSC), wide-angle X-ray scattering (WAXS), and Fourier transform infrared (FTIR) spectroscopy. Quenched amorphous samples have been cold-crystallized at 140 or 170°C for various crystallization times. The degree of crystallinity obtained from WAXS, with the ratio of the crystal peak intensity to the total peak intensity, shows excellent agreement with the crystallinity determined from TMDSC total heat flow endotherms. For the first time, FTIR results show that the absorbance peak ratio (I 981cm Ϫ1/I 1026cm Ϫ1) has a linear correlation with the crystalline mass fraction ( c ) for cold-crystallized iPS according to the following relation: I 981cm Ϫ1/I 1026cm Ϫ1 ϭ 0.54 c ϩ 0.16. This relationship allows the crystallinity of iPS to be determined from infrared spectroscopy analyses in cases in which it is difficult to perform thermal or X-ray measurements. On the basis of the measurements of the heat capacity increment at the glass transition, we find that a significant amount of the rigid amorphous fraction (RAF) coexists with the crystalline and mobile amorphous phases in cold-crystallized iPS. The RAF increases systematically with the crystallization time, and a greater amount is formed at a lower crystallization temperature. A three-phase model (crystalline phase, mobile amorphous phase, and rigid amorphous phase) is, therefore, appropriate for the interpretation of the structure of cold-crystallized iPS. The origin of the low-temperature endothermic peak (annealing peak) has been investigated with TMDSC and FTIR spectroscopy and has been shown to be due to irreversible relaxation of the RAF.

The molecular relaxation processes and structure of isotactic polystyrene (iPS) films were investigated with real-time dielectric spectroscopy and simultaneous wide-and small-angle X-ray scattering. The purpose of this work was to explore the restrictions imposed on molecular mobility in the vicinity of the ␣ relaxation (glass transition) for crystallized iPS. Isothermal cold crystallization at temperatures of T c ϭ 140 or 170°C resulted in a sigmoidal increase of crystallinity with crystallization time. The glass-transition temperature (T g ), determined calorimetrically, exhibited almost no increase during the first stage of crystal growth before impingement of spherulites. After impingement, the calorimetric T g increased, suggesting that confinement effects occur in the latter stages of crystallization. For well-crystallized samples, the radius of the cooperativity region decreased substantially as compared with the purely amorphous sample but was always smaller than the layer thickness of the mobile amorphous fraction. Dielectric experiments directly probed changes in the amorphous dipole mobility. The real-time dielectric data were fitted to a Havriliak-Negami model, and the time dependence of the parameters describing the distribution of relaxation times and dielectric strength was obtained. The central dipolar relaxation time showed little variation before spherulite impingement but increased sharply during the second stage of crystal growth as confinement occurred. Vogel-Fulcher-Tammann analysis demonstrated that the dielectric reference temperature, corresponding to the onset of calorimetric T g , did not vary for well-crystallized samples. This observation agreed with a model in which constraints affect primarily the modes having longer relaxation times and thus broaden the glass-transition relaxation process on the higher temperature side.

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