Dynamic mechanical spectroscopy applied to study the thermal and photodegradation of poly(2,6-dimethyl-1,4-phenylene oxide)/high impact polystyrene blends

The thermal and photooxidative degradation of high impact polystyrene (HIPS) and its blends with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) have been studied under accelerated conditions. HIPS and its blends containing 40, 50 and 60% of PPO, called PPO 40, PPO 50 and PPO 60, were submitted to thermal (ASTM-D5510) and photochemical (ASTM-G53) ageing. The extent of degradation was accompanied by infrared spectroscopy (FTIR), Raman spectroscopy (FT-Raman) and dynamic mechanical analysis (DMA). FTIR and DMA are techniques very sensitive to chemical groups and to relaxation of polymers, respectively. DMA showed that the glass transition of the polybutadiene phase of the external layers of aged HIPS and its blends is shifted to higher temperatures in comparison to non-aged reference samples. The deeper the analysed layer, the more the Tg is shifted to the Tg of the reference material. By FTIR analysis, it was possible to register spectroscopic changes only in the outermost layer (80 μm) while, by DMA, it was possible to detect changes at least to 800 μm depths. The FT-Raman showed that the cis units are the first to be degraded, which explains the shift of the Tg of the polybutadiene phase.