Infrared studies of thermal oxidative degradation of polystyrene-block-polybutadiene-block-polystyrene thermoplastic elastomers

Thermal oxidative degradation of a polystyrene-block-polybutadiene-block-polystyrene thermoplastic elastomer (SBS rubber) has been conducted in an in-situ infrared cell. By monitoring the disappearance of trans-1,4 and vinyl-1,2 double bonds and the appearance of the hydroxyl and the carboxyl/carboxylate carboxylate groups in the FTIR spectra, the temperature, air, antioxidant, and molecular microstructure dependence of the polymer degradation was studied. The experimental results indicate that the 1,4-polybutadiene portion of the SBS polymer is easier to degrade than the 1,2-polybutadiene portion and the hydroxyl group appears concomitantly with the disappearance of the polybutadiene. Based on data from the temperature-programmed desorption (TPD) of H2O, it is concluded that the formation of hydroxyl group makes the polymer hydrophilic and promotes the H2O adsorption on it. The amount of H2O adsorption varies with the temperature and the process appears reversible. At low temperatures, the moisture adsorbed onto a degraded polymer sample amounts to approximately 7-10% of total hydroxyls. 1 wt% of Irganox 1076 (antioxidant) would effectively thwart the thermal oxidation process even at severe conditions as high as 225 degrees C for 12 h. No degradation occurs in an air-free environment. (C) 1996 Elsevier Science Limited