Synthesis of well-defined Y-shaped zwitterionic block copolymers via atom-transfer radical polymerization

A series of well-defined Y-shaped (AB(2)-type) zwitterionic block copolymers were synthesized by atom-transfer radical polymerization (ATRP). First, a bishydroxy-functional ATRP initiator was synthesized by esterification of 2-hydroxyethyl acrylate with 2-bromoisobutyryl bromide, followed by Michael addition using excess diethanolamine. 2-(Diethylamino)ethyl methacrylate (DEA) was polymerized via ATRP using this bishydroxy-functional initiator. The bromine end groups of PDEA were then quantitatively removed by radical chain transfer using excess N,N,N',N",N"-pentamethyldiethylenetri-amine (PMDETA). Esterification of the omega-bishydroxyl end groups using excess 2-bromoisobutyryl bromide afforded a PDEA-based omega-bifunctional macroinitiator [PDEA-(Br)(2)]. A series of Y-shaped zwitterionic PDEA-(PSEMA)(2) [PSEMA poly(succinyloxyethyl methacrylate)] block copolymers were synthesized via ATRP of 2-hydroxyethyl methacrylate (HEMA) using this PDEA-(Br)(2) macroinitiator, followed by reacting the HEMA hydroxyl groups with succinic anhydride. The 'schizophrenic' micellization character of these Y-shaped zwitterionic block copolymers in aqueous solution was confirmed by H-1 NMR spectroscopy, aqueous electrophoresis, and dynamic light-scattering studies.