FT-IR PAS depth profiling investigation of polyethylene surface sulfonation

The treatment of polymers with fuming sulfuric acid is a well-known procedure for introducing \ue5f8SO3H groups onto the polymer surface. FT-IR photoacoustic difference spectroscopy is used to follow the treatment of low density polyethylene with H2SO4\ub7SO3 over the course of 24h. Using the unique depth profiling capability of photoacoustic spectroscopy, the extent of the reaction with the polymer and the distribution of the reaction products across the polymer film are monitored. The present spectroscopic results demonstrate that under the chosen conditions (room temperature and 32% SO3 in H2SO4) surface sulfonation initially dominates, but at longer reaction times (>70 min) oxidation becomes the main process. Phase modulated (PM) depth profiles reveal limited penetration of \ue5f8SO3HSO3 groups, while at long reaction times there is significant carboxylation of the bulk polymer. The extent of hydration into the polymer membrane parallels the extent of oxidation. The implications of the competition between surface sulfonation and bulk oxidation-hydration on the biocompatibility of low density polyethylene is discussed.Peer reviewed: YesNRC publication: Ye