| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 90 === The influence of cross-linking density on the molecular relaxation near its glass transition temperature of the copolymer ( PMMA-PBA ) is the main category we focus on. In order to learn about the effects of different levels of cross-linking density on the molecular motion, one usually probes for the storage modulus and loss modulus by DMA.
Adding various amounts of cross-linker and using the method of swelling ratio can help us to control and to know the real states about cross-link in copolymer. Moreover, the degradation temperature and glass transition temperature can be measured by TGA and DSC. Thus, we found that the Tg values we got are similar to what can be found in other dissertations when the cross-linking density is low. With the increasement of cross-linking levels, we couldn’t get the data about Tg by DSC gradually. Further, it appears that the glass transition temperature will raise as the cross-linking density becomes higher. In addition, the loss modulus peak would also shift to higher temperature region and the relaxation strength would slow down as well.
Eventually, the results from DMA were analysed using the empirical H-N equation. The fitting parameters, α and β, obtained from the data fitting were used to interpret the relation between molecular motions and structure of polymers based on the model proposed by Schonhals and Schlosser. Taking account of the variation of the values, α and αβ. During the information above, one can judge whether the relaxation behaviors between intra-chain and inter-chain are influenced by cross-link or not. Besides, the activation energy also step up with the increasement of cross-linking density.
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