PH-switchable complexation between double hydrophilic heteroarm star copolymers and a cationic block polyelectrolyte

Double hydrophilic heteroarm star copolymers of poly(methacrylic acid) (PMAA) and polyethylene oxide) (PEO) were synthesized via atom-transfer radical polymerization (ATRP) using the "in-out" method. The synthesis consisted of three steps. Namely, ATRP was applied to the preparation of a star macroinitiator with PEO arms and a cross-linked core resulting from the polymerization of divinylbenzene (DVB) in the first step, chain extension with tertbutyl methacrylate (tBMA) under ATRP conditions, and subsequent hydrolysis of the tert-butyl groups afforded (PEO)_n-PDVB-(PMAA)_n heteroarm star copolymers with a cross-linked microgel core. This novel type of double hydrophilic heteroarm star copolymer can be considered as unimolecular micelles with hybrid coronas. The star copolymers exhibited pH-dependent solubility in water, being soluble at high pH and insoluble at low pH, due to the formation of hydrogen-bonded complexes between the PEO and PMAA arms. A mixed solution of the heteroarm star copolymer and a PEO-b-PQDMA diblock copolymer, where PQDMA is poly(2-(dimethylamino) ethyl methacrylate) fully quaternized with methyl iodide, remained stable in the whole pH range, and exhibited an intriguing pH-switchable complexation behavior accompanied with structural rearrangement.