Patent ID: 7521496

Claim:
A compound represented by the following formula (I): wherein, in formula (I), R 1 , R 2 , R 3 and R4 are identical to or different from each other, and are: a C 2-8 alkyl group having a straight or branched chain, a C 5-10 cycloalkyl group which may have one or more substituents, or a C 6-15 aryl group which may have one or more substituents; or R 1 and R 2 are combined to become an alkylene group represented by the following formula (II) and form the following cyclic structure A together with the oxygen atoms and the phosphorus atom; (in cyclic structure A, —R 1 —R 2 — is the alkylene group); or R 3 and R 4 are combined to become an alkylene group represented by the following formula (II) and form the following cyclic structure B together with the oxygen atoms and the phosphorus atom; (in cyclic structure B, —R 3 —R 4 — is the alkylene group); wherein: the compound indispensably has at least one of cyclic structure A and cyclic structure B; and R 20 is a linking group having formula 67: (in formula 67, R 6 and R 7 may be identical to or different from each other; are either hydrogen, a C 1-6 alkyl group, or C 6-11 aryl group; or R 6 and R 7 may be combined to become a C 4-10 alkylene group which may have one or more substituents, the C 4-10 alkylene group forming the following cyclic structure together with the carbon atom and a total number of carbons of R 6 and R 7 is 0 to 12).