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The physical and gas transport properties of hyperbranched polyimide (HBPI)–silica hybrid membranes with different degrees of modification prepared with a dianhydride, 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, a triamine, 1,3,5‐tris(4‐aminophenoxy) benzene, and a coupling agent, 3‐aminopropyltrimethoxysilane, were investigated. With increasing degree of modification, the inherent viscosity of the hyperbranched poly(amic acid) increased, and the density of the HBPI decreased; this suggested the formation of crosslinking through the coupling agent. Dynamic mechanical analysis and thermomechanical analysis measurements indicated that the mobility of the HBPI molecular chains decreased in the rubbery region and that the free‐volume holes of the HBPI increased in the glassy region because of the increased degree of crosslinking through the coupling agent. The CO2 permeability and CO2/CH4 permselectivity of the HBPI–silica hybrid membranes increased with increasing silica content, with the latter increase being remarkable for the HBPI–silica hybrid membranes with a higher degree of modification. This suggested that the pronounced improvement in the CO2/CH4 permselectivity of the highly modified HBPI–silica hybrid membranes was likely caused by the contributions of both the intrinsic high‐fractional free volume attributed to crosslinking through the coupling agent and the characteristic distribution and interconnectivity of free‐volume holes created by hybridization with silica. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Hyperbranched polyimide-silica hybrids (HBPI-silica HBDs) and hyperbranched polyimide-silica composites (HBPI-silica CPTs) were prepared, and their general and gas transport properties were investigated to clarify the effect of silica sources and preparation methods. HBPI-silica HBDs and HBPI-silica CPTs were synthesized by two-step polymerization of A 2 + B 3 monomer system via polyamic acid as precursor, followed by hybridizing or blending silica sources. Silica components were incorporated by the sol-gel reaction with tetramethoxysilane (TMOS) or the addition of colloidal silica. In HBPI-silica HBDs, the aggregation of silica components is controlled because of the high affinity of HBPI and silica caused by the formation of covalent bonds between HBPI and silica. Consequently, HBPI-silica HBDs had good film formability, transparency, and mechanical properties compared with HBPI-silica CPTs. HBPI-silica HBD and CPT membranes prepared via the sol-gel reaction with TMOS showed specific gas permeabilities and permselectivities for CO 2 /CH 4 separation, that is, both CO 2 permeability and CO 2 /CH 4 selectivity increased with increasing silica content. This result suggests that gas transport can occur through a molecular sieving effect of the porous silica network derived from the sol-gel reaction and/or through the narrow interfacial region between the silica networks and the organic matrix. OPEN ACCESSPolymers 2013, 5 1363

Physical and gas transport properties of amine-terminated hyperbranched polyimide-silica hybrid (AM-HBPI-silica hybrid) membranes prepared with a dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, and a triamine, 1,3,5-tris(4-amino-phenoxy)benzene, were investigated and compared with those of dianhydride-terminated hyperbranched polyimide-silica hybrid (DA-HBPI-silica hybrid) membranes. HBPI-silica hybrid membranes were prepared via sol-gel reaction using hyperbranched polyamic acid of which end groups were modified with silane coupling agents, water and tetramethoxysilane. Although the AM-HBPI membrane was colored to dark brown, optical transmittances of AM-HBPI-silica hybrid membranes increased with increasing silica content. Thermal and dimensional stability of AM-HBPI-silica hybrids are higher than those of DA-HBPI-silica hybrids because of the rigidity of AM-HBPI molecular chains which contain more branching units. Gas permeability and CO 2 /CH 4 selectivity of DA-and AM-HBPI-silica hybrid membranes increased with increasing silica content. Especially, CO 2 /CH 4 selectivity of AM-HBPI-silica hybrid membranes remarkably increased with increasing silica content. This behavior is probably due to the characteristic distribution and interconnectivity of free volume holes created by the incorporation of silica and the high affinity of hydroxyl groups remaining in the silica domain to CO 2 .

The physical and gas transport properties of hyperbranched polyimide (HBPI)-silica hybrid membranes treated with carbon dioxide (CO 2 ) gas were investigated and compared with those of linear-type polyimide-silica hybrid membranes to estimate the influence of the molecular structure and hybridization on the stability of gas transport property. For all of the membranes examined, there was no marked change in the FT/IR spectrum or the UV-VIS spectrum before and after CO 2 treatment, indicating no influence on the polyimide molecular chain and the threedimensional Si-O-Si network themselves by the CO 2 treatment. In HBPI-silica hybrid membranes, it was suggested that CO 2 treatment did not cause deterioration of stability of gas transport property. The reason for this was that the restraints of the micro-Brownian motion or the densification of polyimide molecular chains and the stiffening of the three dimensional silica networks have been induced. In contrast, mild plasticization seems to have been caused in 6FDA-based linear-type polyimide-silica hybrid membranes. In addition, although CO 2 treatment decreased both the gas permeability and the selectivity of non-6FDA-based polyimide membranes, it increased the selectivity of the 6FDA-based polyimide membranes.