Block copolymers self-assembled into vesicles and micelles can significantly increase the fracture resistance of cured epoxies with a minimum impact on glass transition temperature and modulus. This has important implications for the manufacture of printed circuit boards, composites, and other applications.
Triblock copolymers used for these purposes are composed of one block that is immiscible in the thermoset precursors and another one that is initially miscible and does not phase separate during the network formation at least up to very high conversions.
The search of a miscible block for a specific DGEBA hardener combination is not a trivial task due to the variety of mechanisms of network formation involving different types of hardeners and the fact that commercial formulations frequently contain other epoxy monomers apart from DGEBA In this study, The epoxidation of poly (styrene-block-butadiene-block-styrene ) (SBS) is done at different epoxidation degree by using H2O2 in the presence of in situ prepared water/dichloroethane biphasic system. The degree of epoxidation in epoxidised SBS was confirmed by FTIR and 1HNMR analysis. The maximum degree of epoxidation occurs as the epoxidation time is 6 hours. The blends were prepared by solvent casting method.
The miscibility studies shows as the epoxidation degree increases miscibility also increases. From the morphological studies performed using SEM and optical microscopy, it was found that at low epoxidation degree there is a heterogeneous morphology and macroscopic phase separation, as the epoxidation degree increases morphology changes to homogeneous and micro and nanostructures. The cure kinetic studies revealed also that a delay in cure kinetics occurs as the weight percentage of block copolymer increases. The fluctuation in viscosity by rheological measurements confirms the phase separation of non epoxidised polybutadiene units in epoxy matrix.
The mechanical tests have shown that the fracture toughness and impact energy values are enhanced by the addition of epoxidised block copolymer.