신규 열전환 공중합체 고분자 기체 분리막

Abstract

This PhD dissertation is mainly focused on the development of novel thermally rearranged copolymers intending to apply for gas separation membranes. It is targeted to developing novel copolymer membranes based on thermally rearranged polybenzoxazole (TR-PBO) and analyzing the relationships between chemical structures and physical properties as well as gas transport properties. This work focused on improving not only gas permeabilities also mechanical properties for practical gas separation applications. This dissertation is organized into six chapters including the introduction (Chapter 1), four main research parts (Chapter 2-5) and conclusion (Chapter 6). Chapter 1 introduces the state of the art of polymeric membranes in gas separation applications, the mechanisms of gas transport through solid state polymer membranes and the summary of development of thermally rearranged polymers for gas separation membranes for last decade. Chapter 2 introduces the relationship between the thermal properties and the structures of the precursor polymers including several hydroxy polyimides and hydroxy copolyimides. Various chemical structures of precursor polymers were obtained by combining different dianhydrides and hydroxy diamines. In this study, three thermal rearrangement temperatures (TTRs) were defined. TTRs demonstrated that the beginning temperature of thermally rearrangement was significantly dependent on the chemical structures of the precursor polymers which established that there is a linear relationship between TTRs with the glassy transition temperature (Tg) of the precursor polymers. Based on the theory in Chapter 2, in Chapter 3, copolymerization with non-hydroxy diamines, so-called non-TR-able diamines, before thermal treatment was made to obtain thermally rearranged poly(benzoxazole-co-imide)s (TR-PBOIs). These poly(benzoxazole-co-imide)s have much stronger mechanical properties than common TR-PBO and in this way, these materials overcome the mechanical issue of TR-PBO membranes. The relationships with polymer rigidity and gas transport properties were intensively studied and it was concluded that the main characteristics of TR-PBOIs were tuned by the ratio of non-TR-able diamines introduced in the polymer and that the right choice of chemical structures along with the enhancement of rigidity of precursor polymers improved the gas permeabilities while a higher flexibility led to a decrease of gas permeabilities but improved the ideal gas selectivities. In Chapter 4, a new generation of TR-PBOs (spiroTR-PBOs) incorporating spirobisindane moieties into the polymer structure are introduced. Precursor HPIs were prepared using a newly synthesized monomer, 3,3,3’,3’-tetramethyl-1,1’-spirobisindane-5,5’ dimaino-6,6’-diol as hydroxy diamine. SpiroTR-PBO highly improved the mechanical properties, mainly the elongation of membrane, due to the kink structure of spiro segment. Molecular simulation analysis of structure and property of spiroTR-PBO explains that the wide angle distributions present in the macromolecular structure makes to stain against applied out-forces. Moreover, the ladder structure of spiroTR-PBO introduced by the spirobisindane group as well as the kink moiety increases the polymer rigidity which then translates to improvements of the gas permeabilities due to the increase of the fractional free volumes. Chapter 5 studies a new research topic on cross-linking effect of TR copolymers. The monomer employed in this chapter is 1,3-diamino benzoic acid (DABA). This study has permitted to interpret the effect of cross-linking on TR polymers. Consequently, is has been demonstrated that DABA units undergo cross-linking by heat treatment acting as a role of pillars between polymer chains to sustain the polymer chain (increase of rigidity) and the free volume units. Cross-linking of TR copolymers results in about 4-fold and 25 fold increase in gas permeabilities compared with those of non-cross-linked TR-PBO copolymer and HPI precursor. Furthermore, incorporating cross-linking units in TR-PBO obviously generates synergetic effects with thermal rearrangement process not only by increasing gas permeability but also by augmenting the plasticization resistance.