Preparation of pH‐sensitive star‐shaped aliphatic polyesters as precursors of polymersomes

This article reports on the synthesis of a new pH‐sensitive amphiphilic A₂B mikto‐arm star‐shaped aliphatic copolyester [with A = poly(ε‐caprolactone) and B = tertiary amine‐bearing poly(ε‐caprolactone)] with two hydrophobic arms and one hydrophilic arm when protonated at pH = 5.5. First, the ring‐opening polymerization of ε‐caprolactone (εCL) was initiated by an aliphatic diol substituted by an alkyne. The copper(I) catalyzed azide‐alkyne cycloaddition (CuAAC) was use to convert the alkyne into a hydroxyl group prone to initiate the ring‐opening copolymerization of γ‐bromo‐ε‐caprolactone (γBrεCL) and εCL. After the substitution of the bromide atoms into azide functions, the N,N‐dimethylprop‐2‐yn‐1‐amine was grafted onto the azide bearing PCL arm by CuAAC, with the purpose to make the B arm hydrophilic at low pH. The precursors of the A₂B copolymers were characterized by ¹H NMR, SEC, and MALDI‐TOF. As expected, the A₂B copolyester was soluble into water at pH = 5. The formation of polymersomes in water at pH 5 was assessed by DLS and TEM analyses. The effects of the architecture and the molecular weight of the A₂B copolymers on the formation of polymersomes were investigated. Moreover, the versatility of our approach was demonstrated by the synthesis of an AB₂ star‐shaped copolyester. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011