Authors Flemming, P. ; Fery, A. ; Münch, A.S. ; Uhlmann, P.
Title Does chain confinement affect thermo-responsiveness? - A comparative study of the LCST and induced UCST transition of tailored grafting-to polyelectrolyte brushes
Date 21.07.2022
Abstract Polycationic poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) is a polyelectrolyte, which is appealing for the design of switchable surface coatings for sensors, catalysts, or biomaterials owing to its multiresponsiveness upon the variation of external triggers (temperature, ionic strength, pH value). In this study, a robust, efficient, and catalyst-free grafting-to approach is presented for the first time, which enables the preparation of double thermoresponsive (LCST and UCST-type transition) PDMAEMA brushes with well-controlled molecular weight and grafting density. The combination of grafting in the melt via a Huisgen 1,3 dipolar cycloaddition allows us to achieve a wide range of grafting densities (0.08–0.20 chains/nm2) even for polyelectrolyte chains with a high molecular weight of 40·000 g/mol. The synthetic control of the grafting density enables a study of the divergent impact of steric restrictions on mechanistically different thermoresponsive transitions of a homopolymer brush. Whereas a pronounced LCST transition with a reduction in brush layer thickness of more than 40% is observed via spectroscopic ellipsometry at intermediate grafting densities (0.12–0.20 chains/nm2) in 5 mM NaCl solution, the UCST transition, induced by multivalent [Fe(CN)6]3– ions, reaches a remarkable change in layer thickness of ~80% already at the lowest investigated grafting density of 0.08 chains/nm2.
Journal Macromolecules 55 (2022) 6775-6786

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