A (meth)acrylate copolymer obtained by copolymerization of a monomer mixture containing a monomer (A) of the general formula (I), ##STR00001## wherein R.sub.1 is a hydrogen atom or methyl, R.sub.2 is a linear or branched alkylene group having 1 to 8 carbon atoms and Y is a single bond or an oxygen atom, a monomer (B) copolymerizable with the monomer (A) and a crosslinking monomer (C).