To prepare a maleic anhydride (1)-modified epoxymethacrylic resin, 379.12 g low-M bisphenol A resin (Epidian 5) was heated 2 h at 80degreesC, 1 h at 90, 100 and 110degreesC. and 2 h at 120degreesC with 0.041 g hydroquinone, 156.72 g methacrylic acid, 12.73 g I, and 1.35 g K-54 (0.8% total wt. of methacrylic acid +1). IR spectra, acid no., and epoxy no. were determined to follow the reaction which was assumed to have been completed after the acid no. fell beneath an assumed value. The reaction mixture was cooled to 90degreesC and diluted with 450 g of hydroquinone-stabilized styrene to yield a 45% solution of the resin. A system comprising 2 wt. pts. Luperox GZN, 0.6 wt. pt. Co(II) octenoate (1% Co) in styrene, and 1.2 wt. pt. of styrenic 10% NN-dimethylaniline was used to cure I-modified and I-nonmodified resins for 24 h at room temp. and for 4 h at 80degreesC. Viscosity, density, gel time, and max. copolymerization temperature were determined at 25degreesC for the compositions to be cured and in the course of curing. Thermal stability of, and glass transition in the resins were studied over 20-1000degreesC and from -20degreesC to 240degreesC, resp. As compared with the I-nonmodified, the I-modified cured resins showed impact strength, bending strength, bending modulus, and Young's modulus higher by 35%, 26%, 10%., and 5%, resp., and breaking strength and relative elongation at break lower by 6 and 7%, resp. Brinell hardness and bending temperature were unaffected. Chemical resistance of the I-modified resins to xylene, painter's naphtha, aqueous acid, aqueous base, and tap water was studied for 16 weeks at room temperature (Fig. 2).