Synthesis of Poly(ethylene glycol)-block-poly(ethylenimine) Possessing an Acetal Group at the PEG End

A new linear block copolymer of poly(ethylene glycol) (PEG) and poly(ethylenimine) (PEI) possessing an acetal group at the PEG chain end was prepared by a heterotelechelic PEG macroinitiator technique. Heterotelechelic PEG with an acetal group at one end and a methanesulfonic group at the other end (acetal-PEG-SO 2 CH 3 ) was synthesized by the anionic ring-opening polymerization of ethylene oxide (EO) initiated with potassium 3,3-diethoxypropanolate (PDP), followed by end-capping with methanesulfonyl chloride. Acetal-PEG-SO 2 CH 3 was then used as a macroinitiator for the cationic ring-opening polymerization of 2-methyl-2-oxazoline (Oz) to form the block copolymer, acetal-PEG-POz. The block efficiency attained almost 100%, allowing to control the molecular weight of the POz segment by the initial monomer/initiator ratio. Alkaline hydrolysis of the repeating acetyl groups in the POz segment gave the completely deacylated block copolymer retaining the acetal group at the PEG chain end. The acetal-PEG-poly(ethylenimine) block copolymer thus obtained may have a potential utility as targetable DNA carrier in the field of gene delivery.