Synthesis of Novel Epoxy Resins by Radical Copolymerization of Various Vinyl Ethers having an Epoxy Group with N-Phenylmaleimide and Properties of Their Cured Resins

To develop novel epoxy resins having both high adhesion and excellent heat resistance, radical copolymerizations of 4-vinyloxybutyl glycidyl ether (VBGE) or 2-(2-vinyloxyethoxy)ethyl glycidyl ether (VEEGE) with N-phenylmaleimide (NPMI), in addition to copolymerization of 2-vinyloxyethyl glycidyl ether (VEGE) with NPMI, which was reported in our previous study, were carried out. The effects of flexibility of the central chain unit of epoxy-containing vinyl ethers (VEs) on the thermal, mechanical, and adhesive properties of the obtained copolymers were investigated. These radical copolymerizations using AIBN as an initiator in benzene at 60 ̊C afforded copolymers having number-average molecular weights of 91,000 to 161,000 in high yield. 1H NMR analysis showed that the structure of the obtained copolymers consisted of VBGE unit or VEEGE unit and NPMI unit. The glass transition temperature (Tg) of the copolymers depended on the composition of the copolymers and decreased as the flexibility of the pendant moiety of VE units increased. The thermal decomposition temperature (Td) of the obtained copolymers was higher than 300 ̊C, indicating their high heat resistance. Tensile shear adhesion strength and tensile strength of the cured copolymers (epoxy content: 2.52~2.63 mmol/g) obtained by curing reaction with polyfunctional aromatic amines were measured. Tensile shear adhesion strength was 1.8 to 4.6 N/mm2 and tensile strength was 21 to 28 MPa, which was found to depend on the flexibility of the pendant moieties of the VE units in the copolymer.