Patent ID: 6846889

Claim:
A copolymer comprising from 20 to 100% by weight of at least one phosphate monomer (a) unit of the following general formula (1), from 0 to 80% by weight of at least one (meth)acrylate monomer (b) unit, and from 0 to 30% by weight of the other monomer (c) unit copolymerizable with them, and the glass transition temperature of the copolymer is 80° C. or less: wherein, R 1 in the formula represents hydrogen atom or methyl group, each R 2 and R 3 independently represents hydrogen atom, or an alkyl group or an alkyl ether group having from 1 to 8 carbon atoms, or an aryl group, and A represents an alkylene group having from 2 to 14 carbon atoms or a polyoxyalkylene group; and wherein tan δ at 25° C. and 10 Hz is 0.5 or more.