In the formula [B], R3 is an alkyl group of 3-20 carbon atoms or a halogenated alkyl group of 3-20 carbon atoms; B6 is --O-- or a single bond; B7, B8 and B9 are each independently --COO--, --OCO-- or a single bond; A4 and A5 are each independently a group selected from the group consisting of ##STR5## or a single bond; m is an integer of 1 to 3; and R4 is an alkyl group of 2-5 carbon atoms.