Coupling of Carboxylate-PEG Derivatives

To the stirring mPEG solution, add several 0.5 g aliquots of solid succinic anhydride over a period of several hours. 

Evaporate the pyridine solvent by using a flash evaporator or a rotary evaporator under vacuum. 

Redissolve the residue in water (the solution may have to be heated to fully dissolve) and again evaporate to dryness. Repeat until the odor of pyridine is nearly gone. 

Remove remaining reactants by dialysis against water using a membrane having a molecular weight cutoff of 1,000. 

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