Effects of the solubility parameter of polyimides and the segment length of siloxane block on the morphology and properties of poly(imide siloxane)

Abstract

The dependence of morphology of the poly(imide siloxane)s (PISs) on the solubility parameter of unmodified polyimides and the molecular weight and content of alpha,omega-bis(3-aminopropyl) polydimethylsiloxane (APPS) has been studied. The effect of the morphology on the mechanical properties is also under investigation. The domain formation in the PISs with the APPS molecular weight M-n = 507 g/mol is not found until the mol ratio of APPS/PIS greater than or equal to 0.5% in the pyromellitic dianhydride/p-phenylene diamine (PMDA/p-PDA)-based PISs, and at a mol ratio greater than or equal to 2.7% in the 3,3',4,4'-benzophenone tetracarboxylic dianhydride/2,2'-bis[4-(3-aminophenoxy)phenyl] sulfone (BTDA/m-BAPS)-based PISs. As the APPS M-n = 715 g/mol, the critical APPS concentrations of the domain formation in both types of PISs are equal to 0.1 and 1.1%, respectively. The critical concentration is equal to 0.6% in the BTDA/m-BAPS-based PIS film with the APPS M-n = 996 g/mol. The isolated siloxane-rich phase in the BTDA/m-BAPS-based PISs becomes a continuous phase as the ,ol ratio of APPS/PIS greater than or equal to 7.7, 10.0, and 16.6% as the APPS M-n = 996, 715, and 507 g/mol, respectively. Dynamic Mechanical Analysis (DMA) shows two T(g)s in the PIS films having phase separation: one at -118 similar to -115 degrees C, being the siloxane-rich phase, the other at 181-244 degrees C, being the aromatic imide-rich phase. The SEM micrographs show a significant deformation on the fractured surfaces of the BTDA/m-BAPS-based PIS films with a continuous siloxane-rich phase. This phenomenon of plastic deformation is also observed in the tensile tests at -118 degrees C and at room temperature. The highest elongation in the PIS films is found at the critical siloxane content of the continuous siloxane-rich phase formation. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2832-2847, 1999.