| Concerning the formation and properties of asymmetric polymeric membranes, this thesis research can be classified into two major categories. In the first part, membranes were developed by thermally induced phase separation (TIPS) techniques and characterized by both scanning electron microscopy (SEM) and mercury intrusion analysis. The effects of the phase separation mechanism, solvent properties, and coarsening on the formation of microporous polymethylmethacrylate (PMMA) membranes were investigated. Experimental observations indicated that during the very early stage of phase separation by spinodal decomposition, a lacy, interconnected membrane structure with good material strength results. In contrast, a fragile membrane structure composed of strings of small beads is a consequence of the early stages of phase separation by nucleation and growth. This study illustrates that a detailed phase diagram is the key to a true understanding of the formation of microcellular structure. For the first time in a membrane formation study, detailed cloud point and spinodal curves were obtained by both optical density and differential scanning calorimetry (DSC) techniques. For membranes prepared by quickly quenching viscous polymer solutions into the demixing region, the membrane morphology observed by SEM can be interpreted consistently in accordance with the location of the metastable and unstable regions as determined by DSC. In designing a well-defined structure with good material strength, this study illustrates not only the importance of the phase diagram but also the significance of choosing a system viscous enough to inhibit phase separation from nucleation and growth during quenching to the unstable region.; In the second part, PMMA was modified by covalently incorporating a photoresponsive unit (trans-4-stilbene methylacrylate or TSMA) into the PMMA backbone as a side group. A novel photoresponsive copolymer (poly(MMA-co-TSMA)) with various ratios of comonomer compositions was developed by free radical copolymerization and characterized by NMR spectroscopy. Its photoresponsive behavior in both solution and solid state was then investigated by various techniques. Significant changes upon irradiation in viscosity, solubility, the glass transition temperature (Tg) and gas permeability were observed. In terms of permeability, this study suggests an excellent potential for developing photoregulatable thin-film composite membrane. |
