Paper Title
Phase Separation Behavior and Fracture Toughness of Novel In-Situ Toughened Epoxy Systems

Abstract
In order to improve the fracture toughness of a cured epoxy system, novel polysulfone-analogues toughening agent such as poly[1,4-bis(azidomethyl)benzene-clicked-4,4sulfonylbis(propynyloxy)benzene][poly(p-BAB/SPB)]and polyetheretherketone-analoguoustoughening agents, i.e., poly[1,4-bis(azidomethyl)benzene-clicked-4,4-bis(2-propynyloxy)benzophenone] [poly(pBAB/PBP)]have been synthesized by using azide-alkyne click reaction, respectively. The epoxy resin based on Triglycidyl p-aminophenol (TGAP) and 4,4'-diaminodiphenyl sulfone (DDS) was toughened with poly(p-BAB/SPB) and poly(p-BAB/PBP) by in-situ azide-alkyne click polymerization during the cure process of the epoxy resin. Another epoxy system based on 2,2-bis[4-(2,3-epoxypropoxy) cyclohexyl]propane (EPCP, Hydrogenated bisphenol A type epoxy) and Isophoronediamine(IPDA) was toughened withaliphatic type of toughening agent such as poly[1,4-Cyclohexane diazidomethane-clicked-polycarprolactonediacetylene (poly(CYDA/PCLDEA) by in-situ azide-alkyne click reaction also . The novel PES-type or PEEK-type polymer toughened epoxy systems showed excellent improvement of fracture toughness below10wt% content of in-situ toughener, compared to preformed polymer toughened epoxy system. The fracture toughness of 10wt% In-situ poly (p-BAB/SPB)and poly(p-BAB/PBP)-toughened TGAP/DDS epoxies (1.83and 1.72MN•m3/2) was 2 times higher than that of the neat TGAP/DDS epoxy (0.9 MN•m3/2).Also, the other aliphatic-type polymer toughened epoxy system showed significantly high value(2.56MN•m3/2) of fracture toughness. The hompgeneousphase for the fracture surface of in-situ toughened epoxiesin SEM micrographs were quite different from the two-phase morphology for the preformed polymer toughened epoxies. All these results might be attributed to the formation of the semi-interpenetrating polymer networks (semi-IPN) composed of the TGAP/DDS network and linear poly(p-BAB/SPB) or poly(p-BAB/PBP) polymer chain. Keywords - Azide-alkyne click polymerization, In-situ Toughened Epoxy system, Semi-interpenetrating Polymer Networks(Semi- IPN), Toughening