PURPOSE: To obtain a copolymer self-cured or crosslinked together with an active hydrogen-containing material to be capable of forming a well crosslinked film by copolymerizing a mono-adduct of a specific compd./amino compd. and an ethylenically unsaturated compd.

CONSTITUTION: A mono-adduct of isopropenyl-α,α-dimethylbenzylisocyanate to an amino compd. and an ethylenically unsaturated compd. copolymerizable with the mono-adduct are copolymerized to obtain a copolymer containing a large number of segments represented by the formula (wherein L and M are each an integer of 1 or more; A is an amino compd. core; R is H, an alkylol or an alkoxyalkyl; R1 and R2 are each H, cyano, a halo, an alkoxy, an acyl, aminocarbonyl, an aryl, a 1-20C alkoxycarbonyl or the like; and (n) is 1 or more). This copolymer is self-cured or crosslinked together with an active hydrogen-containing material to make it possible to generate a film showing good acid resistance characteristics, environmental etching resistance power and good balance of hardness and flexibility after curing.