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 α,ω-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 Mn = 507 g/mol is not found until the mol ratio of APPS/PIS ≥ 0.5% in the pyromellitic dianhydride/p-phenylene diamine (PMDA/p-PDA)-based PISs, and at a mol ratio ≥ 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 Mn = 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 Mn = 996 g/mol. The isolated siloxane-rich phase in the BTDA/m-BAPS-based PISs becomes a continuous phase as the mol ratio of APPS/PIS ≥ 7.7, 10.0, and 16.6% as the APPS Mn = 996, 715, and 507 g/mol, respectively. Dynamic Mechanical Analysis (DMA) shows two Tgs in the PIS films having phase separation: one at −118 ∼ –115°C, being the siloxane-rich phase, the other at 181–244°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°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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2832–2847, 1999