Synthesis of Heterotelechelic Poly(ethylene glycol)‐block‐poly(succinimide) Possessing Both Acetal andTert‐Butoxycarbonyl‐amino Terminals with Narrow Molecular Weight Distribution

A novel heterotelechelic linear block copolymer of poly(ethylene glycol) (PEG) and poly(succinimide) (PSI) possessing both acetal and tert ‐butoxycarbonyl‐amino (Boc‐NH) terminals (Acetal‐PEG‐ b ‐PSI‐NH‐Boc) with a narrow molecular weight distribution (MWD) was successfully prepared by the nucleophilic attack of triethylamine (TEA) to the poly( β ‐benzyl L‐aspartate) (PBLA) segment of Acetal‐PEG‐ b ‐PBLA‐NH‐Boc. Acetal‐PEG‐ b ‐PBLA‐NH‐Boc with MWD of 1.07 was prepared by living anionic ring‐opening polymerization of β ‐benzyl L‐aspartate N ‐carboxy‐anhydride with α ‐acetal‐ ω ‐amino PEG as a macroinitiator, followed by Boc protection. The subsequent conversion of PBLA segment to PSI was successfully carried out by reacting with the catalytic amount of TEA. The characterization by 1 H NMR, GPC and IR demonstrates that the formation of poly(succinimide) proceeded completely without any remarkable side reactions. Acetal‐PEG‐ b ‐PSI‐NH‐Boc thus obtained may have a potential utility as a targetable drug carrier in the field of drug delivery system.