orementioned bivalent groups, or a bivalent group represented by formulae (1-a), (1-b), or (1-c): in which R1, R2, R3, and R4 are each independently an alkyl group which may have a substituent, an aryl group which may have a substituent, or a halogen atom; a and b are each independently an integer of 0 to 4; c and d are each independently an integer of 0 to 3; and l is an integer of 0 or 1, and wh