THERMAL-STABILITY OF HIGH-PERFORMANCE POLY(ARYL ETHER SULFONES) - STRUCTURE-REACTIVITY RELATIONSHIPS IN THE PYROLYSIS OF OLIGOMERIC MODEL COMPOUNDS

The model oligomers 2,2-bis[[4-(phenylsulfonyl)phenoxy]phenyl] propane (ISO) and 4,4'-bis[4(phenylsulfonyl)phenoxy]-1,1'-biphenyl (BP) were reacted neat in argon at 425 OC to compare the thermal stability of poly(aryl ether sulfones). Sulfur dioxide was the major gas product, BP generating a slightly higher evolution rate. The weight-average molecular weight increased with reaction time for both oligomers, but after 60 min, the rate of increase was higher for BP. A quantitative molecular level explanation of these observations focuses on the reactive isopropylidene link in ISO. Fission of the weak Ph-SO2-Ph bond produces phenyl radicals that abstract hydrogen and add to the oligomer backbone. The latter reaction results in increases in M(W) and a net weakening of the aryl-SO2 bond, which leads to increased rates of SO2 evolution. The value of the relative rate, R(rel), of radical addition to H-abstraction was higher for BP than for ISO due to easily abstractable isopropylidene hydrogens.