The evolution of microstructure of Styrene-Isoprene-Butadiene Rubber during the thermal-oxidative aging process using In-situ FTIR way

The thermal-oxidative aging of Styrene-Isoprene-Butadiene Rubber (SIBR) has been studied using transmission spectroscopy in In-situ. These In-situ FTIR imaging results have interpreted the microstructure and mechanism of SIBR in the thermal-oxidative aging process. The conjugated carbonyl group is generated in SIBR during the aging process because SIBR contains both cis 1,4-polyisoprene and 3,4-polyisoprene units. The generation rate of the conjugated carbonyl group in SIBR is significantly increased with the prolonged aging time. Moreover, due to the larger side groups in the 3,4-polyisoprene unit, it needs a higher temperature in the aging process to generate the conjugated carbonyl group. Based on the changes of methylene and -C-O bond during the aging process, the thermal-oxidative aging of SIBR has been found that the cross-linking reaction and chain scission reaction take place simultaneously, but the cross-linking reaction dominates the degradation. Compared with Solution-polymerizated-Styrene-Butadiene Rubber (SSBR) and Nd-Polyisoprene Rubber (Nd-IR), the thermal-oxidative aging rate of SIBR is between SSBR and Nd-IR in view of the changes in carbonyl group and –CO structure during the aging process.