Patent ID: 8668933

Claim:
A polyion complex consisting of a double-stranded ribonucleic acid and a block copolymer of formula (I) or (II), which are electrostatically bound together, wherein the polyion complex has an average particle diameter of less than 50 nm as measured by a dynamic light scattering measuring method, and wherein the block copolymer and the double-stranded ribonucleic acid are present in a ratio of N/P=1.2 to 1.5, wherein N represents the total number of cations in the block copolymer, and P represents the total number of phosphoester bonds or equivalent bonds in the double-stranded ribonucleic acid: wherein each of R 1a and R 1b independently represents a hydrogen atom or an unsubstituted or substituted linear or branched C 1-12 alkyl group, each of L 1 and L 2 represents a linkage group, R 2 represents a hydrogen atom, a protecting group, a hydrophobic group or a polymerizing group, R 3 represents a hydroxyl group, an oxybenzyl group, an —NH—(CH 2 ) a —X group (X is an amine compound residue comprising one kind or two kinds or more of a primary, secondary or tertiary amine or a quaternary ammonium salt, or a non-amine compound residue; a is an integer of 1 to 5) or an initiator residue, each of R 4a and 4b independently represents a hydrogen atom, a protecting group for amino group or —C(═NH)NHR 5 (R 5 represents a hydrogen atom or a protecting group for an amino group), m represents an integer of 5 to 20000, n represents an integer of 2 to 5000, and x represents an integer of 1 to 5.