Phase structure and phase transitions in semicrystalline isotactic polystyrene

Semicrystalline polymers have been recognized as being in a non-equilibrium, metastable state. A single molecule can participate in several phase regimes. Thus, interpretation of the phase structure of semicrystalline polymers, and an understanding of their correspondent phase transitions are essential aspects in today's polymer physics research. The ultimate goal of this thesis is to provide general descriptions regarding understanding the metastable phase structure and correspondent phase transitions in semicrystalline polymers based on the study of simple homopolymer isotactic polystyrene. This thesis gives a detailed description about characterizing the phase structure of semicrystalline isotactic polystyrene. More importantly, this thesis investigates the most hotly debated issues regarding the phase transitions observed in semicrystalline polymers, i.e., formation (vitrification) and relaxation (devitrification) of the rigid amorphous fraction, reversible melting of crystals of semicrystalline polymer, and interpretation of multiple melting of semicrystalline polymer.;In this thesis, semicrystalline isotactic polystyrene (iPS) is obtained using two different mechanisms---crystallization from the glassy state, or crystallization from dilute solution. The experimental techniques including thermal analysis, X-ray scattering and Fourier transform infrared spectroscopy, are used to characterize the phase structure and phase transitions for both semicrystalline WS systems. The main topics contained in this thesis are: (1) Phase structure of semicrystalline isotactic polystyrene. For the WS sample crystallized from the glassy state, the experimental evidence demonstrates that the phase structure can be interpreted by a three-phase stack model comprising mobile amorphous, rigid amorphous and crystalline fractions. The phase structure of WS samples crystallized from dilute solution can be interpreted by either a two-phase or a three-phase model depending upon the sample treatment. (2) Formation (vitrification) and relaxation (devitrification) of rigid amorphous fraction. The rigid amorphous fraction is suggested to be located at the interface between the mobile amorphous and crystalline fractions. The time development (kinetics) of phase formation shows that the rigid amorphous fraction in WS is established mostly during secondary crystallization. The real time quasi-isothermal crystallization measurements demonstrate that the rigid amorphous fraction forms at the crystallization temperature for a well crystallized WS sample. (3) Reversible melting and multiple melting of semicrystalline isotactic polystyrene. The melting behavior of cold crystallized, or solution grown crystals of PS is investigated by thermal analysis and X-ray scattering. (Abstract shortened by UMI.)...