Polymer having halogen-containing segment and pharmaceutical composition using same

A polymer represented by the following formula (I), (II), (III), or (IV):

• wherein R1 and R2 are each independently a hydrogen atom or an optionally substituted C1-12 alkyl group,
• R3 is a side chain of any amino acid,
• A is a single bond or a hydrophilic polymer chain,
• L1a and L1b are each independently a single bond or a linking group,
• L2 is a single bond or L3,
• L3 is a linker represented by the formula (V) or (VI):
• wherein m and n are each independently an integer of 0 to 5,
• * on the left side is a bonding position to an —NH— group, and
• * on the right side is a bonding position to a carbonyl group,
• B is a C1-20 haloalkyl group,
• D is a cation-containing group, an anion-containing group, or a group represented by the formula (VII):
• wherein t is an integer of 0 to 5,
• ** is a bonding position to a —(CH2)q— group, and
• G is O or NH,
• E is an NHCOR group, an NHCOOR group, a CONHR group, or a COOR group,
• R is an alkyl group having 3 to 20 carbon atoms or a group derived from a lipid,
• z is an integer of 2 to 500,
• x is an integer that is not less than 40% of z,
• y is an integer that may be 0,
• w is an integer that may be 0,
• z-x-y-w is an integer that may be 0,
• z-x is an integer that may be 0,
• p, q and r are each independently an integer of 1 to 10, and
• s is an integer of 0 to 10.
• (provided that, in the formulas (III) and (IV), (i) when A is a single bond, then (ii) m is an integer of 0 to 2).