Synthesis and characterization of pH- and thermo-responsive hydrogels based on poly(2-cyclopropyl-2-oxazoline) macromono
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Synthesis and characterization of pH‑ and thermo‑responsive hydrogels based on poly(2‑cyclopropyl‑2‑oxazoline) macromonomer, sodium acrylate, and acrylamide Juan Carlos Rueda1 · Carlos Suárez1 · Hartmut Komber2 · Stefan Zschoche2 · Brigitte Voit2 Received: 6 July 2019 / Revised: 23 September 2019 / Accepted: 25 November 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract New graft copolymer hydrogels based on sodium acrylate, acrylamide, and styrylterminated poly(2-cyclopropyl-2-oxazoline) macromonomer (MM) were synthetized by free radical polymerization using N,N′-methylenebisacrylamide as crosslinker. The polymerization was carried out in water at 5 °C and was initiated by sodium peroxodisulfate/N,N,N′,N′-tetramethylethylenediamine. The MM and the hydrogels were characterized by NMR and FTIR spectroscopy. In the hydrogels, the sodium acrylate provided the sensitivity to changes in pH value while the MM provided sensitivity to temperature. In dependence of their composition, the bi-sensitive hydrogels showed conformational transitions with variation of temperature or pH value. This property was shown macroscopically as a hydrogel volume contraction or expansion as it was determined by swelling experiments in water at different pH values and temperatures. Due to phase separation within the hydrogels facilitated by the graft copolymer network structure, both sensitivities could be addressed individually by both triggers and defined swelling states could be addressed over a wide range by adjusting both temperature and pH.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s0028 9-019-03034-0) contains supplementary material, which is available to authorized users. * Brigitte Voit [email protected] 1
Polymer Laboratory, Physical Section, Research Department (DGI), Pontifical Catholic University of Peru (PUCP), Box 1761, Lima, Peru
2
Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, 01069 Dresden, Germany
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Polymer Bulletin
Introduction Responsive polymeric materials are polymers that go through a phase transition in response to an external stimulus such as temperature, pH, magnetic field, electrical impulses, and light [1–5]. This type of material is being investigated for its potential applications in biomedicine, water management, in sensors and as actuators, among others [6, 7]. Currently, many polymers that respond with changes in their solubility in aqueous solution depending on the changes of temperature are been studied in the literature [2, 5, 8]. Among them, one of the most studied is poly(N-isopropylacrylamide) (PNiPAAm), since its minimum critical solution temperature (LCST) in water, which is the temperature at which the polymer changes from hydrophilic to hydrophobic, is close to the temperature of the human body [2, 5, 8, 9]. In recent years, the thermal sensitivity of some polyoxazolines has also been investigated, such as, for example, poly(isopropyloxazoline) (poly(iPrOxa)), poly(cyclop
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