Time-resolved fluorescence anisotropy studies of the temperature-induced intramolecular conformational transition of poly(N-isopropylacrylamide) in dilute aqueous solution
Time-resolved fluorescence anisotropy studies of the temperature-induced intramolecular conformational transition of poly(N-isopropylacrylamide) in dilute aqueous solution
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聚（N-异丙基丙烯酰胺）在稀水溶液中温度诱导的分子内构象转变的时间分辨荧光各向异性研究
DOI：
10.1016/s0032-3861(96)00636-2
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发表时间：
1997
期刊：
影响因子：
4.6
通讯作者：
L. Swanson
中科院分区：
文献类型：
--
作者：
C. Chee;S. Rimmer;I. Soutar;L. Swanson
在稀溶液中，以甲醇和水为溶剂，测量了事件标记的(0.5%)聚N-异丙基丙烯酰胺(PNIPAM)样品的时间分辨荧光各向异性。在甲醇中，PNIPAM的链段松弛在所研究的温度范围内遵循阿累尼乌斯方程，其“活化能”为13.4(±0.5)kJ·−~(-1)，仅略大于溶剂流动的活化能(约2.4kJ·−~(-1))，很可能是PNIPAM与甲醇之间的特殊偶极相互作用决定了该溶剂中的大分子动力学。在水溶液中，PNIPAM的链段迁移率在约32°C表现出明显的热可逆间断，这种构象行为的变化发生在聚合物在水介质中的较低临界溶液温度。这一观察结果支持了(Winnik，F.M.Polmer 1990，31,2125)的命题，即该体系中的热诱导分离是通过一种‘双模式’机制发生的，其中分子间聚集之前是聚合物线圈的分子内构象收缩。
Time-resolved fluorescence anisotropy measurements have been performed upon an acenaphthylene-labelled (0.5 mol%) sample of poly(N-isopropylacrylamide), PNIPAM, in dilute solutions in both methanol and water as solvents. In methanol, segmental relaxation of PNIPAM follows an Arrhenius dependence upon temperature over the range investigated (279–323K) characterized by an ‘activation energy’ of 13.4(±0.5) kJ mol−1. This is only slightly greater (by ca 2.4 kJ mol−1) than that of solvent flow and it is likely that specific dipolar interactions between the PNIPAM and the methanol determine the macromolecular dynamics in this solvent. In aqueous solution, the segmental mobility of PNIPAM exhibits a dramatic thermoreversible discontinuity at ca 32°C. This change in conformational behaviour occurs at the polymer's lower critical solution temperature in aqueous media. This observation, supports the proposition (Winnik, F. M. Polymer 1990, 31, 2125) that the thermally-induced separation in this system occurs by a ‘dual mode’ mechanism wherein intermolecular aggregation is preceded by intramolecular conformational shrinkage of the polymer coils.