he general formula (I): wherein R1 is hydrogen atom or methyl group; R2 is a halogen atom, hydroxyl group, mercapto group or ???O???R3???OH group, wherein R3 is an alkylene group having 6 to 25 carbon atoms; and Y is oxygen atom or sulfur atom; and (c) at least one hydrophilic polymerizable monomer selected from the group consisting of hydroxyalkyl (meth)acrylates having an alkylene group of 2 or