Experimental and Theoretical Studies on the Phase Behavior of Aqueous Solutions of Structurally Controlled Hyperbranched Poly(<i>N</i>-isopropylacrylamide)s
Experimental and Theoretical Studies on the Phase Behavior of Aqueous Solutions of Structurally Controlled Hyperbranched Poly(<i>N</i>-isopropylacrylamide)s
复制标题
结构控制超支化聚(<i>N</i>-异丙基丙烯酰胺)水溶液相行为的实验与理论研究
DOI：
10.1021/acs.macromol.2c01162
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发表时间：
2022
期刊：
影响因子：
5.5
通讯作者：
Koga Tsuyoshi
中科院分区：
文献类型：
--
作者：
Kojima Hiroyuki;Imamura Yuji;Lu Yangtian;Yamago Shigeru;Koga Tsuyoshi
系统地合成了具有不同支化密度的超支化聚（N-异丙基丙烯酰胺）（HB-PNIPAMs），低临界溶解温度（LCST），在水中进行了研究。分枝显著影响LCST，并且它们随着分枝密度的增加而减小。从协同水合作用的概念出发，对实验结果的来源进行了理论分析，协同水合作用是指聚合物链与水分子之间连续形成氢键。假设水化的协同性不传播超过分支点，我们计算了旋节曲线，双节曲线和临界点，并构建相图。还计算了子链、支化点和端基的水合程度，以考察它们对相行为的水合作用。在这项研究中，我们考虑了以下两种情况：（i）只有子链可以水合，（ii）HB聚合物的每个部分，包括支化点和端基，都可以水合。我们比较的理论与结构良好的控制HB-PNIPAM在水中的浊点的观测报告。定性协议是通过使用相同的值的协同线性PNIPAM的水溶液的研究。我们还表明，端基和支化点的水化行为强烈影响相行为，并说明双节点温度是由其水化促进水化作用和抑制水化作用之间的平衡决定的，因为支化点抑制协同水化。
Structurally controlled hyperbranched poly(N-isopropylacrylamide)s (HB-PNIPAMs) having different branching densities were systematically synthesized, and their phase behavior, i.e., lower critical solution temperatures (LCSTs), in water was studied. The branching significantly affects LCSTs, and they decrease with an increase in the branching density. The origin of the experimental results was theoretically analyzed on the basis of the concept of cooperative hydration, which is the sequential formation of hydrogen bonds between polymer chains and water molecules. Assuming that the cooperativity of hydration does not propagate beyond the branching points, we calculate the spinodal curves, binodal curves, and critical points and construct the phase diagrams. The degrees of hydration of the subchains, branching points, and end groups are also calculated to examine their hydration effect on the phase behavior. In this investigation, we consider the following two situations: (i) only subchains can be hydrated, and (ii) every part of HB polymers, including branching points and end groups, can be hydrated. We compare the theory with the reported observations of the cloud points of structurally well-controlled HB-PNIPAMs in water. Qualitative agreement is obtained by using the same value of cooperativity as the study of aqueous solutions of linear PNIPAMs. We also show that the hydration behavior of the end groups and the branching points strongly influences the phase behavior and illustrate that the binodal temperature is determined by the balance between the effect of promoting hydration by their hydration and suppressing hydration due to the inhibition of cooperative hydration by the branching points.