| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 96 === Miscibility and stereocomplex structures formation in blends of stereoregular isotactic and syndiotactic poly(methyl methacrylate)s (i- and s-PMMA) were investigated in this study using differential scanning calorimetry (DSC), polarized-light optical microscope (POM), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical analysis (DMA). Miscibility was first confirmed as a preliminary step. The series of binary blends of aPMMA/iPMMA, aPMMA/sPMMA, and iPMMA/sPMMA all exhibited a single, composition-dependent glass transition and homogeneous phase morphology. The aPMMA/iPMMA blend exhibited a cusp in Tg-composition relationship, which could be described by Kovacs equation, with a g value of -0.042. The aPMMA/sPMMA and iPMMA/sPMMA blend could be described by Gordon-Taylor equation, with k values of 0.38 and 0.36, respectively.
This work further investigated the solvent-induced stereocomplex structures in of ternary iPMMA/sPMMA blend by adding poly(ethylene oxide) (PEO). Although formation of a stereocomplex structure in binary iPMMA/sPMMA blend is known to be kinetically hindered in noncomplexing CHCl3 solvent, stereocomplexation was found to be apparently enhanced by introducing PEO in the iPMMA/sPMMA blend. Mechanisms and influencing factors (such as thermal treatment, annealing temperature, annealing time, or PEO content in blends) on structures of stereocomplexes in the ternary iPMMA/sPMMA/PEO blends are discussed. WAXD result showed that addition of PEO to iPMMA/sPMMA blend did not alter the crystal cells in the complexes. Melting peaks associated with the complexes were analyzed for discerning possible structural mechanisms. When annealed at specific temperatures, multiple endothermic peaks of the complexes increased in intensity as PEO contents were increased in the ternary blends. Analysis shows that the lower melting peak represents shorter stereocomplex sequences or stereocomplex detached from PEO or connected with partial PEO but the higher melting peak is related to the stereocomplex interconnected with PEO. In addition, the stereocomplex could “decomplex” and the prior solvent and/or thermal histories disappeared upon heating to 240oC. Upon heating to 240oC to erase all prior thermal histories and then annealed at specific temperatures, the ternary blends would exhibit reproducible complexes; however, such complexes were not present in the binary iPMMA/sPMMA blend without PEO. Physical interaction or miscibility-enhanced chain entanglement likely exists between PEO and the stereocomplex of tactic PMMAs, leading to stereocomplex formation in the iPMMA/sPMMA/PEO ternary blend. FT-IR characterization provided evidence of weak interactions between PEO and the stereocomplex of PMMA. IR peaks sensitive to complex structures with respect to temperature were analyzed for discerning effects by adding PEO. The stereocomplex formation of ternary blends is probable due to the weak interaction of ester groups and methoxy groups between PMMA and PEO.
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