Abstract
The microphase separation of double-hydrophilic block copolymers in water is of interest when these copolymers are utilized as molecular assemblies with mesoscale aqueous compartments. Diblock copolymers composed of a water-soluble zwitterionic polymer, poly(carboxybetaine acrylate) (PCBA2), and a hydrophilic water-insoluble nonionic polymer, poly(2-methoxyethyl acrylate) (PMEA), (PCBA2n-b-PMEAm) were synthesized, and their assembly characteristics were investigated in aqueous solutions. Well-defined PCBA2n-b-PMEAm block copolymers were synthesized by the reversible addition–fragmentation chain transfer polymerization of a carboxybetaine acrylate modified with a tert-butyl group and 2-methoxyethyl acrylate followed by tert-butyl group cleavage. PCBA2n-b-PMEAm produced particles in dilute aqueous solutions and microphase-separated structures in concentrated aqueous solutions. The hydrodynamic radius of the particles and the microphase-separated structure were associated with the block copolymer composition and degree of polymerization of the PMEA chain. The molecular assembly behavior was tolerant to NaCl concentration, providing molecular design guidelines for the use of double-hydrophilic microphase-separated compartments in physiological environments.
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Acknowledgements
This work was supported by JSPS KAKENHI Grant Number JP22H02147 (Grant-in-Aid for Scientific Research (B)) and JP22H04555, JP19H05714, JP19H05720 (Grant-in-Aid for Scientific Research on Innovative Area: Aquatic Functional Materials). YH acknowledges the Toshiaki Ogasawara Memorial Foundation for its financial support. This work was performed under the Cooperative Research Program of “Network Joint Research Center for Materials and Devices”. Synchrotron SAXS experiments were performed on the BL06 and BL11 beamlines at the SAGA Light Source (proposal numbers 2022IIK013, 2211113 F). The authors acknowledge Dr. M. Kawamoto for his assistance with the SAXS measurements. The authors gratefully acknowledge Prof. Emi Hifumi (Oita University) for her help in conducting the DLS measurements. The following supplementary information is available at the Polymer Journal website: measurements; synthesis of 2-(N-(2-acryloyloxyethyl)-N,N-dimethyl)ammonio)-1-(tert-butoxy)-1-oxoethane bromide (tert-BuCBA2); 1H-NMR spectrum of P(tert-BuCBA2)-CTA and PCBA2; appearance of PMEA76, PCBA229, and PCBA229-b-PMEA199 salt-free aqueous solutions; Rh distributions of PCBA2n-b-PMEAm in 150 mM NaCl aqueous solutions; correlation function profile for the PCBA233-b-PMEA146 60 wt% salt-free aqueous solution; phase contrast optical microscopy image of the coacervate droplets in PCBA233-b-PMEA146 solutions; and SAXS data for polymer concentration-dependent PCBA229-b-PMEA34 aggregation in salt-free aqueous solutions.
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Higaki, Y., Toyama, H., Masuda, T. et al. Microphase separation of double-hydrophilic poly(carboxybetaine acrylate)-poly(2-methoxyethyl acrylate) block copolymers in water. Polym J 55, 1357–1365 (2023). https://doi.org/10.1038/s41428-023-00831-3
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DOI: https://doi.org/10.1038/s41428-023-00831-3