Programmed Self-Assembly Systems of Amphiphilic Random Copolymers into Size-Controlled and Thermoresponsive Micelles in Water

• Published in: Macromolecules Vol. 51; no. 2; pp. 398 - 409
• Main Authors: Imai, Shota, Hirai, Yuji, Nagao, Chitose, Sawamoto, Mitsuo, Terashima, Takaya
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23.01.2018
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.7b01918

We report programmed self-assembly systems of amphiphilic random copolymers bearing hydrophilic poly­(ethylene glycol) (PEG) and hydrophobic alkyl pendants into size-controlled and thermoresponsive micelles in water. This system affords simultaneous and precise control of the size, aggregation numbers, and cloud point (Cp) of micelles in water by primary structure (pendant alkyl groups, composition, and chain length) that is programmed in the copolymers. Typically, random copolymers bearing PEG and alkyl pendants (butyl, octyl, dodecyl, and octadecyl groups) universally induce intermolecular self-assembly in water to produce uniform size micelles (<10 nm). The size is just determined by the content and alkyl pendant length of the hydrophobic monomers, independent of main chain length (below critical length for self-folding): The size increased with increasing the content and the pendant length. Design of hydrophobic alkyl groups with tuning composition allow us to widely control the size (molecular weight: 20K–1350K) and cloud point (from 45 to 85 °C) of the polymer micelles. We can thus tailor-make various micelles with identical size yet different Cp or those with identical Cp yet different size. Thanks to such dual controllability, self-sorting and stepwise thermoresponsive micelle systems were also created with blends of different copolymers; binary copolymers induced orthogonal self-assembly in water to provide discrete micelles with different size and cloud point.