Study Of Phase Separation Behavior Of Polymer Blends And Heterogeneous Polymerization Of Polymer Hydrogels By Optical Methods

Optical techniques play important roles in the study of physical properties of polymeric materials, because one can obtain large amount of valuable information about microstructure of the materials by using optical techniques without the needs of destroying it. Furthermore, one can study the dynamic process in real time by using optical methods. In this dissertation, the time-resolved small angle light scattering (SALS) technique was employed to study the temperature dependence of spinodal decomposition (SD) behavior of LCST type polymer blends and founded the real-time laser light refraction technique to study the spatial distribution of refractive index in hydrogels during polymerization. According to the Cahn-Hilliard theory, the apparent diffusion coefficient Dapp linearly depends on temperature when approaching the equilibrium spinodal temperature. The equilibrium spinodal temperature can be obtained by linear extrapolating Dapp into zero. This linear phase separation behavior could be observed in polystyrene/polyvinylmethylether (PS/PVME) blends. However, as reported in the literature, this linear regime couldn抰 be observed in some other systems such as PC/PMMA, PS/PMsC and other polymer blends. To better understand this nonlinear phase separation behavior, poly(methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMAISAN) blend system was selected in this dissertation and its phase separation behavior was investigated by using SALS method during isothermal annealing and heating process. It was found that phase separation of PMMA/SAN blends follows the SD mechanism over the temperature range from 1450C to 2080C. It was also found experimentally that no linear regime for apparent diffusion coefficient and phase separation rate can be observed over the experimental temperature range, which was much larger than that investigated by other authors. Therefore, it was impossible to obtain the equilibrium spinodal temperature by any linear extrapolation. This indicated that the experimental temperature is much higher than the equilibrium spinodal temperature. At lower temperatures, phase separation was too slow to be observed within a limited time because of thc poor motility of macromolecules at temperature close to glass transition temperature. Therefore, when determine the equilibrium phase diagram of polymer blends like PMMA/SAN by using the isothermal annealing method, it should be noted that when temperature is close to the glass transition temperature, phase separation rate is very slow and it is hard to observe obvious phase separation behavior within limited time. It was further found that the evolution of scattering intensity over a large temperature range follows the time-temperature superposition (TTS) principle could be described by the Williams-Landel-Ferry (WLF)-like function. In early stage of phase separation, time dependent scattering intensity 1(t) and temperature dependent apparent diffusion coefficient Dapp(T) can be related by WLF-like function. In coarsening process, the evolution of domain size can also be described by WLF-like function. The reason for the nonlinear phase separation behavior is that the interaction parameter between PMMA and SAN weakly depends on temperature and the phase separation kinetics within the temperature range under investigation is mainly controlled by the diffusion behavior of macromolecules and viscosity of the melts, which follows the well-known ITS principle. It is also found that the SD behavior of polystyrene/poly(methyl methacrylate-stat-c...