Abstract
3,3’-(methylene-1,4-diphenylene)bis(3,4-dihydro-2H-1,3-benzoxazine) (P-d type benzoxazine, P-d) was toughened by two different toughening technologies. Toughening by employing in situ generated alternating copolymer of styrene with N-phenylmaleimide (PMS) as modifier could not be applied to P-d owing to the inhibition of a propagation of PMS polymerization in the presence of P-d. Therefore, we employed bisphenol-A diglycidylether (DGEBA) as a medium for radical polymerization of PMS. Phase separated structure in cured resins was given by the employment of DGEBA, and thus fracture toughness (KIC) was increased by 55%. On the other hand, the solubility parameters (SPs) of the modifier monomers were judiciously manipulated to prevent the inhibition of in situ generation of modifiers, by selecting novel modifiers, such as n- butyl methacrylate and styrene, with SPs that differ from SP of the matrix. By adopting this approach, KIC of P-d modified with novel in situ generated modifiers was successfully increased by 43% without sacrificing flexural strength that is unique property of polybenzoxazines.
