FT-IR PAS DEPTH PROFILING INVESTIGATION OF POLYETHYLENE SURFACE SULFONATION

The treatment of polymers with fuming sulfuric acid is a well-known pr ocedure for introducing -SO3H groups onto the polymer surface. FT-IR p hotoacoustic difference spectroscopy is used to follow the treatment o f low density polyethylene with H2SO4 . SO3 over the course of 24 h. U sing the unique depth profiling capability of photoacoustic spectrosco py, the extent of the reaction with the polymer and the distribution o f the reaction products across the polymer film are monitored. The pre sent spectroscopic results demonstrate that under the chosen condition s (room temperature and 32% SO3 in H2SO4) surface sulfonation initiall y dominates, but at longer reaction times (> 70 min) oxidation becomes the main process. Phase modulated (PM) depth profiles reveal limited penetration of -SO3H/SO3 groups, while at long reaction times there is significant carboxylation of the bulk polymer. The extent of hydratio n into the polymer membrane parallels the extent of oxidation. The imp lications of the competition between surface sulfonation and bulk oxid ation-hydration on the biocompatibility of low density polyethylene is discussed.