Synthesis and micellization properties of double hydrophilic A ₂BA₂ 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 A₂B A₂ and A₄B A₄ 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 (DBA) 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 ¹H 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.