R1 is an alkylene group having from 3 to 5 carbon atoms, a has an average value of 0 to 300 and b has an average value of 0 to 30, a+b has an average value of 2 to 60, x has an average value of 1 to 500 and y has an average value of 0 to 100, and containing at least 1 Q group in each molecule.