A synthetic hydrogel with thermoreversible gelation, III: an NMR study of the sol–gel transition
A synthetic hydrogel with thermoreversible gelation, III: an NMR study of the sol–gel transition
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具有热可逆凝胶作用的合成水凝胶，III：溶胶-凝胶转变的核磁共振研究
DOI：
10.1002/pat.1994.220050207
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发表时间：
1994
影响因子：
3.4
通讯作者：
J. A. Cushman
中科院分区：
文献类型：
--
作者：
H. Yoshioka;Y. Mori;J. A. Cushman
用NMR研究了聚N-异丙基丙烯酰胺（PNIPAAm-PEG）与聚乙二醇（PEG）的共聚物（PNIPAAm-PEG）的溶胶-凝胶转变机理。在99.9%D2O中的PNIPAAm-PEG溶液上测量的1H-和13 C-NMR光谱显示在热诱导的水凝胶形成期间，PNIPAAm嵌段的线宽增宽大于PEG嵌段的线宽增宽。这一结果表明，在凝胶化过程中，PNIPAAm嵌段的流动性比PEG嵌段的流动性更受限制。交联聚合物网络的形成是通过凝胶化过程中残留HDO质子的自旋-晶格弛豫时间（T1）的突然减少来确定的。PNIPAAm和PEG嵌段的T1值的温度依赖性表明，PNIPAAm嵌段在水中的微观条件在凝胶化过程中发生了急剧变化，而PEG嵌段的微观条件没有变化。NMR的实验结果支持以下的凝胶化机制，即由疏水相互作用引起的PNIPAAm嵌段在单独的共聚物中的聚集形成交联点，以给出无限的三维网络结构。共聚物中的水合PEG链为网络提供了在水中的溶胀性质，并防止聚集引起宏观相分离。
The sol–gel transition mechanism of a thermoreversible hydrogel composed of a copolymer comprising poly(N-isopropylacrylamide) and poly(ethylene glycol) (PNIPAAm–PEG) was studied by NMR. The 1H– and 13C–NMR spectra measured on a PNIPAAm–PEG solution in 99.9% D2O showed a remarkable line width broadening of the PNIPAAm block of more than that of the PEG block, during thermally induced hydrogel formation. This result suggested that the mobility of the PNIPAAm block is more restricted than that of the PEG block during gelation. A crosslinked polymer network formation was ascertained by a sudden reduction in the spin-lattice relaxation time (T1) of the residual HDO proton during gelation. The temperature dependency of the T1 values for the PNIPAAm and PEG blocks revealed that the microscopic condition of the PNIPAAm block in water was drastically changed during gelation, while that of the PEG block was unchanged. The experimental results from NMR supported the following gelation mechanism; that an aggregation of PNIPAAm blocks in the separate copolymers caused by hydrophobic interaction forms crosslinking points to give an infinite three-dimensional network structure. The hydrated PEG chains in the copolymers provide the network with a swelling property in water, and prevent the aggregation from causing a macroscopic phase separation.