. . . "In the above formula, P is a hydrogen atom, hydroxyl group, epoxy ring (OCH2CH???), alkoxy group having 1-4 carbon atoms, alkylcarbonyloxy group having 1 to 6 carbon atoms, or alkylcarbonyl group having 1 to 6 carbon atoms; Q1, Q2, Q3, and Q4 are independently ???CqH2q-pPp??? (wherein P is the same definition as above, p is an integer from 0 to 3, and q is an integer from 0 to 10); u is an integer" . .