Highly cross-linked soluble star copolymers with well controlled molecular weights

• Heteroarm star copolymers have been synthesized with well-controlled structure.
• They are soluble and have stimuli-responsive blocks providing surface activity.
• They can form micelles in aqueous media depending on solution pH.
• They form smaller micelles than that of the linear-analogs under same conditions.
• Finally, they have lower viscosity and CMC values than that of the linear-analogs.

We report the synthesis and characterization of water soluble star copolymers based on 2-(N-dimethylamino)ethyl methacrylate, 2-(N-diethylamino)ethyl methacrylate, and 2-(N-morpholino)ethyl methacrylate monomers via group transfer polymerization. Ethylene glycol dimethacrylate was used as a branching agent. Highly cross-linked heteroarm star copolymers were obtained with narrow molecular weight distributions and controlled molecular architectures. Star copolymers were obtained in good yield with a monomer/branching agent at the appropriate mole ratio without macrogelation. Additionally, analog linear diblock copolymers with similar comonomer ratios were also synthesized to make comprehension. Star copolymers had lower viscosities compared to linear analogs at pH 8.1. Critical micelle concentration and critical micellization pH values were also determined for these star copolymers and compared to linear diblock copolymers. All polymers were characterized using gel permeation chromatography combined with a light scattering and a refractive index detectors and 1H NMR spectroscopy, to determine the molecular weights, molecular weight distributions and comonomer compositions, respectively. Solution behaviors of the polymers were also analyzed with a viscometer, densitometer, and surface tensiometer.

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