10 carbon atoms, and R7 is an alkyl group having from 1 to 10 carbon atoms, b is an integer of from 0 to 4, and c is 0 or 1.Examples of such a radical-polymerizable organic group include 2-acryloyloxyethyl, 3-acryloyloxypropyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-vinylphenyl, 3-vinylphenyl, 4-(2-propenyl)phen