Distribution of chlorosulfonyl groups in the subsurface of polystyrene substrates. Analysis by means of vibrational spectroscopy

In this work the activation of transparent PS substrates by chlorosulfonation is described and their distribution in the subsurface region is analyzed using vibrational spectroscopies. Confocal Raman microspectroscopy is shown to be insufficiently surface selective and only the highest modified samples can be analyzed using a mathematical procedure for the correction of diffraction effects on the depth profile. On the other hand, FTIR-ATR spectroscopy carried out using different internal reflection elements and varying angles of incidence allows discrimination between the different modification profiles including those with low modification degrees obtained at low treatment times. The results show that the electrophilic aromatic substitution of polystyrene in pure chlorosulfonic acid is extremely quick with the complete surface covered by chlorosulfonic groups after only 10 min reaction time at -10 °C. It is further demonstrated that the reaction is very surface selective and that even after reaction times as long as 3 h the modification is limited to a layer with a thickness of less than one m.