Influences Of Phase Separation On The Crvstallization Behavior Of PVDF/PMMI

In this dissertation, a novel crystalline/amorphous polymer blend, poly(vinylidene fluoride)/poly(n-methyl methacrylimide) blend was selected as model system to investigate the effect of liquid-liquid phase separation (LLPS) on crystallization behavior by using differential scanning calorimetry(DSC) and Polarizing Optical Microscope(POM). Furthermore, the kinetics of isothermal crystallization of PVDF/PMMI was discussed by Avrami theory.Two kinds of PMMI with different Tg were adopted to prepare blends, and they are named as PMMI1(Tg≈172℃) and PMMI2(Tg≈131℃) respectively. It is found that both the nulceation density and spherulite growth rate decrease with the increase of PMMI1during isothermal crystallization. In addition, the increase of half-time of crystallization (t1/2) for PVDF/PMMI1indicates that the addition of PMMI1leads to the increae of isothermal crystallization rate, but PMMI1has little effect on crystallizatoin rate of the non-isothermal crystallization. The addtion of PMMI2results in a dramatical decrease in spherulite growth rate, the increase of nucleation density during isothermal crystallization and the improvement of crystal perfection. The isothermal crystallization kinetics of PVDF/PMMI blends can be well described by Avrami model. It follows the prenucleation and three dimensional growth mode.According to the kinetic analytic results of isothermal crystallization for PVDF/PMMI1blend which undergo LLPS, it was found that the isothermal crystallization kinetics could still be described by Avrami theory and the t1/2increases, indicating that the crystallization rate decreases after phase separation. However, the effect of LLPS on non-isothermal crystallization of PVDF/PMMI1is very weak. For the PVDF/PMMI2, both the nucleation density and spherulite growth rate decrease during isothermal crystallization after the phase separation happened. In the non-isothermal crystallization, the crystallization exothermic peak shifts to low temperature and the peak width increases after phase separation, indicating a decreased nucleation and crystallizaiton ability.