PURPOSE: To prepare the titled composition giving a cured product having excellent heat resistance, and suitable as a raw material of surface-protecting paint, casting resin, molding resin, and impregnating resin, by compounding a specific unsaturated compound, a polymerizable unsaturated compound, etc.

CONSTITUTION: The composition is prepared by compounding (A) 95W50pts.wt. of an unsaturated compound of formula [R1 is H of methyl; R2 is glycol residue or a straight-chain polyester oligomer residue of formula -(R'-COO-R"-COO)m-R'-(R' is glycol residue; R" is dibasic acid residue; m is 1W20); R3 is diisocyanate residue; n is 1W10], (B) 5W50pts.wt. of a compound having one or more polymerizable unsaturated groups in a molecule [e.g. (meth)acrylic acid (ester)], and (C) 0W 10pts.wt. of a radical polymerization initiator and/or a photosensitizer.