Futscher Moritz H, Philipp Martine, Müller-Buschbaum Peter, Schulte Alfons
Technische Universität München, Physik-Department, Lehrstuhl für Funktionelle Materialien, James-Franck-Str. 1, 85748, Garching, Germany.
University of Central Florida, Department of Physics and College of Optics and Photonics, 4111 Libra Drive, Orlando, FL, 32817-2385, United States.
Sci Rep. 2017 Dec 5;7(1):17012. doi: 10.1038/s41598-017-17272-7.
Thermo-responsive polymers undergo a reversible coil-to-globule transition in water after which the chains collapse and aggregate into bigger globules when passing to above its lower critical solution temperature (LCST). The hydrogen bonding with the amide groups in the side chains has to be contrasted with the hydration interaction of the hydrophobic main-chain hydrocarbons. In the present investigation we study molecular changes in the polymer poly(N-isopropyl acrylamide) (PNIPAM) and in its monomer N-isopropyl acrylamide (NIPAM) in solution across the LCST transition. Employing Fourier-transform infrared spectroscopy we probe changes in conformation and hydrogen bonding. We observe a nearly discontinuous shift of the peak frequencies and areas of vibrational bands across the LCST transition for PNIPAM whereas NIPAM exhibits a continuous linear change with temperature. This supports the crucial role of the polymer backbone with respect to hydration changes in the amide group in combination with cooperative interactions of bound water along the backbone chain.
热响应性聚合物在水中会经历可逆的线圈到球体转变，当温度超过其低临界溶液温度（LCST）时，链会塌陷并聚集成更大的球体。侧链中酰胺基团的氢键作用必须与疏水主链烃的水合作用形成对比。在本研究中，我们研究了聚合物聚（N-异丙基丙烯酰胺）（PNIPAM）及其单体N-异丙基丙烯酰胺（NIPAM）在溶液中跨越LCST转变时的分子变化。利用傅里叶变换红外光谱，我们探测构象和氢键的变化。我们观察到PNIPAM在LCST转变过程中振动带的峰值频率和面积几乎是不连续的变化，而NIPAM则随温度呈现连续的线性变化。这支持了聚合物主链在酰胺基团水合变化方面的关键作用，以及结合水沿主链链的协同相互作用。
