The thermal decomposition of poly(butene-1 sulfone), poly(pentene-1 sulfone), poly(hexene-1 sulfone), poly(styrene sulfone), and polystyrene was investigated in helium at a heating rate of 20°C/min using an experimental system which consists of a programmable pyrolyzer, a thermal conductivity detector, a mass chromatograph, and a vapor-phase infrared spectrophotometer. Poly(butene-1 sulfone), poly(penetene-1 sulfone), and poly(hexene-1 sulfone) displayed two-step decomposition; the primary products of decomposition at both steps were the comonomers (olefin and SO2). For poly(styrene sulfone), in addition to styrene and SO2, products with molecular weights corresponding to dimers of styrene were observed. Decomposition of this polymer was compared with that of polystyrene, which formed mostly monomer.