| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === In this study, syndiotactic polystyrene (sPS, Mw~200 kg/mol) was blended with different tacticities polystyrene. We used 50/50 weight ratio to blend with three different kinds of molecular weight atactic polystyrene (aPS-M, Mw~3.68 kg/mol; aPS-H, Mw~300 kg/mol; aPS-U, Mw~1880 kg/mol), and blended different ratios (70/30, 50/50 and 30/70) with isotactic polystyrene (iPS, Mw~300 kg/mol). Then, I will discuss the crystallization behavior and morphology of these blends by a new design—time-temperature-resolved FTIR.
The first part is cold crystallization experiment. For neat sPS system, the average n value is about 2.9. Using WLF equation, we can figure out that the activation energy of the sPS chain diffusion is ca. 5.2 kJ/mol. In different molecular weight aPS system, the k values of sPS/aPS-H and sPS/aPS-U blend are bigger than the one of sPS, whereas the k value of sPS/aPS-M blend is smaller than the one of sPS. For all of these sPS/aPS blends, the average n value is about 2.5. In sPS/iPS blend system, we can find the phase separation on melt state. Going a step further to discuss the crystallization behavior, we can observe the two step crystallization obviously by plotting relative crystallinity versus time. And the n values have big difference with different iPS blend ratio (70/30, 50/50 and 30/70)－2.7, 2.2 and 1.1 individually.
In the melt crystallization experiments, we focus on a crystallized temperature－Tc=250 oC to discuss sPS/aPS blend. Unlike the cold crystallization result, the k values of sPS/aPS blend are smaller than the one of sPS. On the other hand, we design the two step crystallization experiment－250 oC to 175 oC to carry out the crystallization behavior of sPS/iPS blend system. The result shows that the higher the iPS blend ratio, the lower the n value－3.1, 2.9 and 2.3 individually. Besides, some FTIR absorbance peak would take place red shift at high temperature state.
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