Vapor phase silylation of poly(4-hydroxystyrene sulfone) (PHOSS) film was carried out with (trimethylsilyl)dimethylamine (TMSDMA) as a silylation reagent. Infrared spectroscopy was used to follow the silylation. Phenolic hydroxyl groups were trimethylsilylated, but desulfonylation of PHOSS was greatly enhanced simultaneously. The reaction rates were investigated at reaction temperatures of 50, 60, and 70 degrees C. The rate of silylation increased with increasing reaction temperature. However, the rate of desulfonylation was very fast in the presence of TMSDMA and was virtually invariant with reaction temperature. It was confirmed that trimethylsilylation in the polymer side chain of PHOSS enhanced desulfonylation in the main chain. Trimethylsilylation might be expected to lower the ceiling temperature of the polymer.