Thermal and crystallization behaviour of epoxidized high cis-polybutadiene rubber

High cis-polybutadiene (HCBR) was epoxidized by using in situ formed formic acid and hydrogen peroxide in the absence and presence of Tween 20 at 50 degrees C at different reaction times. Epoxidized HCBR (EHCBR) with degree of epoxidation from 3.7 to 38.8% was obtained. Low degree epoxidation EHCBR are semi-crystalline rubbers presenting lower crystallization temperatures than the non-epoxidized rubber on cooling and a cold crystallization and melting temperature on heating, differently from high epoxidation content rubbers (over 10%) which are amorphous materials. Epoxidation increases the glass transition temperature and decreases the melting temperature and the degree of crystallinity of the polybutadiene. The increase of epoxidation also decreases its thermal stability, which drops about 28 degrees C when the content of epoxidation is increased about 30%. Non-isothermal crystallization experiments of HCBR and EHCBR were systematically carried out at cooling rates of 5, 10, 20, and 30 degrees C/min to evaluate the crystallinity developed upon cooling. By increasing the cooling rate, the crystallization enthalpy increases for HCBR while it decreases for EHCBR.