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 ‘ ‘-pentamethyldiethylenetriamine (PMDETA). Esterification of the ω-bishydroxyl end groups using excess 2-bromoisobutyryl bromide afforded a PDEA-based ω-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 1 H NMR spectroscopy, aqueous electrophoresis, and dynamic light-scattering studies.