Patent ID: 8153110

Claim:
A micellar polyion complex, which comprises: a block copolymer constituted by a polyethylene glycol portion and a polycation portion having a side chain whose terminus is a thiol group; wherein the block copolymer is represented by formula (1): wherein each of R 1 and R 2 independently represents a hydrogen atom or a substitutable linear or branched alkyl group containing 1 to 12 carbon atoms; L 1 represents NH, a group represented by formula (2): —(CH 2 ) p1 —NH— (2) wherein p1 represents an integer between 1 and 5, or L 1 represents a group represented by formula (3): -L 2a -(CH 2 ) q1 -L 3a - (3) wherein L 2a represents OCO, OCONH, NHCO, NHCOO, NHCONH, CONH or COO, L 3a represents NH, and q1 represents an integer between 1 and 5; k represents an integer between 100 and 500; m represents an integer between 0 and 499; n represents an integer between 1 and 500; and m+n=10 to 500; p represents an integer between 1 and 10; q represents an integer between 1 and 10; and r represents an integer between 1 and 10, wherein the symbol “/” in formula (1) indicates that the sequence order of respective monomer units described at the left and right sides thereof (the number of units: m+n) is arbitrarily determined and wherein n/(m+n) is greater than or equal to 0.65 and less than or equal to 1; and siRNA.