Degradation of aromatic polymers—I. Rates of crosslinking and chain scission during thermal degradation of several soluble aromatic polymers

Abstract

Five kinds of aromatic polymers [polycarbonate(PC), polyarylate(PAR), polyetherimide(PEI), polysulfone(PSF), polyethersulfone(PESF)] were degraded at 380° in vacuum. The molecular weights and molecular weight distributions of degraded samples were measured by gel permeation chromatography, using dichloromethane as eluent. It was found that crosslinking takes place during degradation of each aromatic polymer studied; chain scission occurs simultaneously to a lesser extent. A novel simulation method, with theoretical calculation of molecular weights of the degraded sample, allowed evaluation of both the crosslinking rate and the chain scission rate. The crosslinking rate decreases in the order PEI > PAR > PC ⪢ PSF ⋍ PESF , and chain scission rate decreases in the order PC > PAR > PEI > PSF > PESF. It is suggested that the isopropylidene moiety and carbonate linkage increase the rate of chain scission, while the aryl sulfone moiety decreases the rate of radical reaction.