Structure-property relationships in block copolymer modified epoxy resins with novel morphologies

Block copolymers self-assemble into ordered or micellar morphologies in cured epoxy depending on the block copolymer concentration in the blend. Curing retains these morphologies providing conditions leading to macroscopic phase separation are avoided. Structure-property investigations on the cured blends revealed that the self-assembled block copolymer morphology influences the fracture resistance improvement in these blends. Addition of block copolymer does not reduce the epoxy glass transition temperature and can even increase it in certain cases. However, the modulus decreased as the block copolymer concentration increased.; Asymmetric block copolymers were examined in uncured and cured epoxy blends, where the shorter epoxy miscible block length results in vesicle or wormlike micelle formation in the dilute block copolymer limit. For an amine-cured epoxy, vesicles produced the highest increases in fracture resistance where these improvements correlate with the vesicle size and separation. Spherical micelles were shown to behave mechanically as small vesicles.; Because of the success in toughening amine-cured epoxies, block copolymers were used to improve the fracture resistance of flame retardant epoxies. First, block copolymers were shown to self-assemble into ordered morphologies in blends containing a brominated epoxy, providing the block copolymer molecular weight was high enough to prevent phase separation. Then, well-dispersed vesicles, wormlike micelles, and spherical micelles were documented in the phenol novolac cured brominated (and nonbrominated) resins and the mechanical properties of these materials were investigated. Wormlike micelles increased the glass transition temperature of the phenol novolac cured brominated and non-brominated epoxies and produced a dramatic increase in the fracture resistance. In fact, the increase in fracture resistance of these blends correlates with the increase in the glass transition temperature. As an added benefit, the modulus of these materials did not decrease significantly. As the glass transition temperature and fracture resistance both increased, these materials contradict the assumption that an increase in toughness necessarily comes at the expense of the use temperature.