Method for producing maleimide polyethylene glycol derivative

A method for producing a maleimide polyethylene glycol derivative represented by the following general formula (2), comprising a reaction step of heating a maleimide polyethylene glycol derivative having a protective group represented by the following general formula (1), in a solvent in the presence of silica gel to cause deprotection:

• wherein R1, R2, R3, and R4 each independently represents a group selected from a hydrogen atom, an alkyl group, a halogen atom, a cyano group, a formyl group, an acyl group, a carboxy group, an acyloxy group, and an alkylcarbonyloxymethyl group,
• Z is a residue obtained by removing active hydrogen groups from a compound having 2 to 5 active hydrogen groups,
• Y1 and Y2 each independently represents a single bond, an ether bond, an amide bond, an ester bond, a urethane bond, a carbonate bond, a thioether bond, a disulfide bond, a thioester bond, or an alkylene group containing any of them,
• W is a group selected from an ether group, a methylene group and a dimethylvinylidene group,
• X is a hydrocarbon group having 1 to 7 carbon atoms, a protective group for a hydroxy group, a protective group for a carboxy group, a protective group for a thiol, a cyano group, or an alkylene group containing any of them,
• m1 and m2 each independently is 1 or 0,
• n1 represents the number of repeating units of the polyethylene glycol and is an integer of 0 or 10 to 2000,
• n2 represents the number of repeating units of the polyethylene glycol and is an integer of 10 to 2000,
• l represents the number of repeating units of the methylene group and is an integer of 0 or 2 to 10,
• a is an integer of 1 to 5, b is an integer of 0 to 4, and the sum of a and b is an integer of 2 to 5.