Coil-to-Globule Transition of PNIPAM Graft Copolymers with Charged Side Chains: A 1H and 2H NMR and Spin Relaxation Study

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• 作者：Mihaela Rusu ; Sebastian Wohlrab ; Dirk Kuckling ; Helmuth Mö ; hwald ; Monika Schö ; nhoff
• 刊名：Macromolecules
• 出版年：2006
• 出版时间：October 17, 2006
• 年：2006
• 卷：39
• 期：21
• 页码：7358 - 7363
• 全文大小：90K
• 年卷期：v.39,no.21(October 17, 2006)
• ISSN：1520-5835

文摘

Graft copolymers of poly(2-vinylpyridine), P2VP, grafted to a backbone of poly(N-isopropylacrylamide), PNIPAM, are investigated concerning their thermosensitive behavior in aqueous solution. ¹H NMRmonitors the coil-to-globule transition by quantifying the fraction of mobile segments in the liquid state. Fieldgradient NMR diffusion studies reveal a decrease of the hydrodynamic radius with temperature as the lowercritical solution temperature (LCST) is approached. The LCST and the width of the transition of PNIPAM areincreasing with grafting density and decreasing upon salt addition, which is attributed to electrostatic forces. Thegrafted segments become partially immobilized only for low grafting density. For high grafting density a fractionof the backbone segments remains mobile even above the LCST. ²H spin relaxation rates of the hydration waterindicate the presence of water molecules with very slow dynamics in the transition regime, whereas above andbelow the transition only fast water dynamics is found.