Synthesis and Micellization Properties of Double Hydrophilic A2BA2 and A4BA4 Non-Linear Block Copolymers

We describe the first account of the synthesis and intriguing micellization properties of nonlinear double hydrophilic block copolymers (DHBCs) of the A2BA2 and A4BA4 type. Atom transfer radical polymerization (ATRP) macroinitiators with two and four initiating sites at both ends of poly(propylene oxide) (PPO) chain were synthesized via reacting 2-hydroxyethyl acrylate and glycidol with commercially available diamine-terminated PPO, respectively, followed by esterification with excess 2-bromoisobutyryl bromide or 2-bromopropionyl bromide. Well-defined nonlinear DHBCs, (PDEA)2PPO(PDEA)2 (H-shaped) and (PDEA)4PPO(PDEA)4 (star-b-linear-b- star), were then prepared by polymerizing 2-(diethylamino)ethyl methacrylate (DEA) via ATRP in 2-propanol at 40 °C using the prepared macroinitiators, where PDEA was poly(2-(diethylamino)ethyl methacrylate). The structures of the resulting nonlinear shaped copolymers were characterized by 1 H NMR and gel permeation chromatography (GPC). The pH- and thermoresponsive micellization behavior of (PDEA10)2PPO(PDEA10)2 and (PDEA11)4PPO- (PDEA11)4 was then investigated by a combination of dynamic laser light scattering (LLS) and fluorescence techniques. Compared to the linear counterpart, the nonlinear block copolymers exhibited complex and interesting micellization properties.