endrimer (C) containing radical-polymerizable organic groups represented by the following general formula (III): in which Y is a radical-polymerizable organic group and R1 and Xi are as hereinabove, and by subjecting them to copolymerization.The vinyl monomers (A) containing fluoro organic groups in the molecule are preferably monomers represented by the general formula:???(CH2)???CR15COORf.