Epoxidation of styrene-isoprene-styrene block copolymer and research on its reaction mechanism

Abstract

Styrene-isoprene-styrene (SIS) block copolymer was modified into epoxidized styrene-isoprene-styrene (ESIS) block copolymer with performic acid generated in situ from hydrogen peroxide and formic acid. The structure and property of ESIS were characterized by Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric/differential thermogravimetric (TG/DTG), melt flow rate (MFR) and dynamic mechanical analysis (DMA), and the reaction mechanism in the process of epoxidation was analyzed. The results showed that C=C double bonds of 1,4-structure were more active than that of 3,4-structure in polyisoprene chains. With epoxidation reaction proceeding, the whole tendency of molecular weight increased and molecular weight distribution widened, and MFR firstly increased and latterly decreased. The heat resistance of ESIS was superior to that of SIS. When SIS was changed into ESIS with 15.3% of mass fraction of epoxide groups, Tg of polyisoprene chains increased from −45.3 °C to 10.9 °C. In the earlier period of epoxidation, some molecular chains ruptured and new substances with low molecular weight formed. However, in the latter period, crosslinking reaction between molecular chains which was initiated by epoxide groups or C=C double bonds occurred and crosslinked insoluble substances came into being.