A multilayered polymer according to claim 1 or 2, wherein the polyalkylene oxide chain-containing unsaturated monofunctional monomer used for forming the third layer is represented by the formula D--O--(RO)n --X (1) wherein D is a group having an unsaturated double bond, R is an alkylene group having 1 to 4 carbon atoms, n is an integer of approximately 5 to 5