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 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 H 2O, it is concluded that the formation of hydroxyl group makes the polymer hydrophilic and promotes the H 2O adsorption on it. The amount of H 2O 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 °C for 12 h. No degradation occurs in an air-free environment.