Abstract
Radical polymerization of vinyl monomers can proceed independently of the non-radical curing reaction of thermosetting resins. Therefore, vinyl polymer modifiers for such thermosetting resins are expected to be prepared in situ during the curing procedure. In this review, we describe toughening of the thermosetting resins using the modifiers prepared in situ by radical polymerization. Utilization of in situ polymerized modifiers is advantageous due to not only its simplified processes and decreased viscosity of the uncured resins but also the achievement of large increase in fracture toughness without sacrificing other properties such as strength and modulus. The in situ prepared alternating copolymer of styrene with N-phenylmaleimide (PMS) modified with polyoxyethylene (POE) was found to be effective for toughening of acid-anhydride-cured epoxy resin with reducing decrease in flexural strength. The modification of cyanate ester resin with the in situ generated PMS grafted with POE and crosslinked by divinylbenzene showed 2.35 times higher fracture toughness than the unmodified resin with keeping flexural strength, flexural modulus and Tg of the original resin. In situ generated crosslinked poly (benzyl methacrylate) toughened amine-cured epoxy resin, to which toughening by in situ generated PMS polymers could not be applied due to the inhibition of the alternating copolymerization by the amine used as a curing agent.
