14) illustrated below, trimethylolpropane tris(3-ethyl-3-oxetanylmethyl) ether shown by the formula (15) illustrated below, and the compounds represented by formula (16) shown below. wherein R1 represents the same group as defined in the formula (2), R8 represents the same group as defined in the formula (7), R11 represents an alkyl group having from 1 to 4 carbon atoms such as a methyl group, eth