Phase separation and thermal aging behavior of styrene-butadiene rubber vulcanizates using liquid polymers as plasticizers studied by differential scanning calorimetry and dynamic mechanical spectroscopy

Styrene-butadiene rubber (SBR) vulcanizates were prepared using plasticizers including the four liquid types of styrene-butadiene copolymers (LPSB), polybutadiene (LPB), polyisoprene (LPI), and the hydrogenated polyisoprene (LHPI) as well as the conventional process oil, and their phase-separated structures and mechanical properties were investigated by differential scanning calorimetry and dynamic mechanical spectroscopy. The phase separation was observed for the SBR vulcanizates when LPI and LHPI were used as the plasticizers, while the LPSB and LPB gave homogeneous structures because of the good miscibility with the SBR. The phase-separated structure of the SBR vulcanizate prepared using LPI changed to the homogeneous during the thermal aging. We revealed the role of the liquid polymers as the plasticizers in maintaining the physical and mechanical properties of the SBR vulcanizates during the thermal aging process when the plasticizers were miscible to the SBR.