Effects of the Solubility Parameter of Polyimides and the Segment Length of Siloxane Block on the Morphology and Properties of Poly(imide siloxane)

摘要

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(s-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 >= 0.5% in the pyromellitic dianhydride/p-pnenylene diamine (PMDA/p-PDA)-based PISs,and at a mol ratio .= 2.7% in the 3,3'4,4'-benzo-phenone tetracarboxylic dianhydride/2,2'-bis[4-(30aminophenoxy) phenyl] sulfone (BTDA/m-BAPS)-based PISs.As the APPS M_n =715 g/mol,the critical APPS concen-trations 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 mol ratio of APPS/PIS >= 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 approx -115 deg C,being the siloxane-rich phase,the other at 181-244 deg 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 ob-served in the tensile tests at - 118 deg 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.