Toughening epoxy resins with epoxidized styrene-butadiene-styrene triblock Co-polymers: The role of molecular topology and epoxidation degree

With the rising demand for structural materials, epoxy resins are widely used despite their low toughness. This study explores enhancing toughness through epoxidized styrene-butadiene-styrene (eSBS). Three types of SBS were examined: Calprene C501 (linear; 17.5% and 25.8% epoxidation), Solprene S4318 (linear, polydispersed; 21% and 34%), and Solprene S9618 (multi-arm; 21% and 38%), with samples at 5 wt % and 10 wt % per epoxidation level. Findings indicate that eSBS effectively promotes shear yielding when the epoxidation degree is above 21%. The toughening mechanisms vary with molecular characteristics. SBS with a smaller radius of gyration promoted a higher strain at break due to the formation of more aligned shear bands, whereas SBS with a larger radius of gyration tended to form interconnected networks within the matrix, thereby delaying yielding failure. This study highlights the importance of block copolymer properties in optimizing epoxy toughness.