Porous polyimide films prepared by thermolysis of porogens with hyperbranched structure

Abstract

Two hyperbranched molecules, benzenetricarboxvlic acid dendritic benzyl ether ester (BTRC-BE) and benzenetricarboxylic acid polyethylene glycol ester (BTRC-PEG), were prepared and tested as pore-generating agents (porogens) for the preparation of porous polyimide. The hyperbranched molecules were thermally stable during the imidization process and completely decomposed well below the decradation temperature of polyimides, indicating that they possessed desirable thermal decomposition characteristics as porogens for the porous polyimide. From the SEM analysis dispersed domains were observed in the poly(amic acid) films containing BTRC-BE, whereas no phase separation was observed in the poly(amic acid) films containing BTRC-PEG. This may be attributable to the different polarities of the porogens because the hydrophobic BTRC-BE was phase-separated in the hydrophilic poly(amic acid) matrix but BTRC-PEG was well mixed with poly(amic acid). The morphology developed in the poly(amic acid) film was retained after imidization and decomposition of the porogens; thus only BTRC-BE produced the porous polyimide. As the content of BTRC-BE decreased from 20 to 5 wt %, the pore size decreased from 390 +/- 100 to 90 +/- 50 nm and the pore density also decreased. (C) 2004 Wiley Periodicals, Inc