PREPARATION AND THERMAL KINETICS OF POLY(IMIDE SILOXANES)

Thermoplastic poly(imide-siloxanes) (PISILs) were synthesized from hexafluoroisopropylidene-2,2-bis(phtalic acid anhydride) (6FDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and amine-terminated poly(dimethyl siloxanes) (PDMS) having different molecular weights. Glass transition temperatures of fully cured PISILs ranged from -91 to -48-degrees-C. Various kinetic parameters for the thermal decomposition reaction of PISILs were examined by dynamic thermogravimetric analysis (DTGA) at four different heating rates. The degradation path was a kinetically first-order reaction for PISILs (abbreviated 6FDA-860, BTDA-860, and PMDA-860, respectively) from 6FDA, BTDA, PMDA, and PDMS (M(n) = 860 g/mol). The reaction rate constant times the half-life (k X t1/2) was approximately 0.693. The activation energies for decomposition were in the following order: 6FDA-860 < BTDA-860 < PMDA-860. The lifetime of the highest heat-resistant PMDA-860 at about 200-degrees-C and at the conversion level of 10% was 6.5 X 10(5) h or 74 years. Other kinetic factors were also calculated. (C) 1993 John Wiley & Sons, Inc.