), p is not less than 2 and R3, R4 and R6 each is a hydrogen atom) such as polyethylene glycol monoacrylate, polypropylene glycol monoacrylate and polybutylene glycol monoacrylate; and various alkoxy(poly)alkylene glycol monoacrylates (corresponding to the case where, in the above general formula (3), R3 and R4 each is a hydrogen atom and R6 is a hydrocarbon group containing 1 to 30 carbon atoms)