Polymer, method for producing polymer, and drug conjugate

A method for producing a polymer, comprising:

• a step (1) of reacting a polymer (P1) which has a repeating unit (II′) represented by Formula (II′) with a compound (1a) represented by Formula (1a) to obtain a polymer (P2) which has a repeating unit represented by Formula (I′) and the repeating unit (II′);
• and
• a step (2) of hydrolyzing the polymer (P2) under a neutral condition or an acidic condition to obtain a polymer which has a repeating unit (I) represented by Formula (I) and a repeating unit (II-1) represented by Formula (II-1)
• wherein m represents 1 or 2, R2 represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group, L represents a divalent aromatic hydrocarbon group, or a divalent aliphatic hydrocarbon group, R1 represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group, Ra11 and Ra12 each independently represent a methyl group or an ethyl group or Ra11 and Ra12 are bonded to each other and represent an ethylene group or a propylene group, and Rx represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group.

A method for producing a polymer, comprising:

• a step (1) of reacting a polymer (P1) which has a repeating unit (II′) represented by Formula (II′) with a compound (1a) represented by Formula (1a) to obtain a polymer (P2) which has a repeating unit represented by Formula (I′) and the repeating unit (II′);
• a step (2a) of applying at least one treatment selected from the group consisting of hydrolysis under an alkaline condition, a transesterification reaction, aminolysis, and hydrolysis and amide coupling under an alkaline condition to the polymer (P2) to obtain a polymer (P3) which has a repeating unit (I′) represented by Formula (I′) and a repeating unit (II) represented by Formula (II);
• and
• a step (2b) of hydrolyzing the polymer (P3) under a neutral condition or an acidic condition to obtain a polymer which has a repeating unit (I) represented by Formula (I) and a repeating unit (II) represented by Formula (II)
• wherein m represents 1 or 2, R2 represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group, L represents a divalent aromatic hydrocarbon group, or a divalent aliphatic hydrocarbon group, R1 represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group, Ra11 and Ra12 each independently represent a methyl group or an ethyl group or Ra11 and Ra12 are bonded to each other and represent an ethylene group or a propylene group, X represents ORx, SRx, or NRx1Rx2, Rx represents a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group, and Rx1 and Rx2 each independently represent a hydrogen atom, an aliphatic hydrocarbon group, or an aromatic hydrocarbon group.