Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)
Effect of the zwitterion structure on the thermo-responsive behaviour of poly(sulfobetaine methacrylates)
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DOI：
10.1039/c6py01220e
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发表时间：
2017-01-07
影响因子：
4.6
通讯作者：
Papadakis, Christine M.
中科院分区：
文献类型：
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作者：
Hildebrand, Viet;Laschewsky, Andre;Papadakis, Christine M.
通过系统地改变两性离子基团的取代基，合成了一系列新的甲基丙烯酸磺基甜菜碱，包括含氮饱和杂环。在三氟乙醇中，通过RAFT(可逆加成-断裂链转移)方法进行的自由基聚合进展顺利，控制良好，得到了具有可预测摩尔质量的聚合物。通过用荧光染料标记端基，便于摩尔质量分析和端基保真度的控制。聚合物在水溶液中表现出明显的UCST(上临界溶液温度)类型的热响应行为，这不能通过对其中包含的亲水和疏水元素的增量分析来简单地与其分子结构相关联。将两性离子部分的氨基和磺酸基的间隔长度从3个碳增加到4个碳，显著提高了相变温度，而将主链上的氨基和羧酸酯基团的间隔长度从2个碳增加到3个碳，则产生了相反的影响。此外，类似的多两性离子的相变温度按二甲基氨>；吗啉>；哌啶基烷基磺酸盐的顺序降低。除了聚合物的精确分子结构的基本效应外，还研究了相变温度对浓度和摩尔质量的依赖关系。此外，我们还考察了添加低摩尔质量盐对氯化钠和溴化钠以及硫酸钠和硫铵水相行为的影响。强效应对盐分浓度的影响是一个复杂的过程。这些影响的强度取决于添加的阴离子的性质，按硫酸盐和氯化物&溴化物的顺序增加，从而遵循经验的霍夫迈斯特系列。相反，改变阳离子时，即添加硫酸钠或硫铵时，没有观察到显著差异。
A series of new sulfobetaine methacrylates, including nitrogen-containing saturated heterocycles, was synthesised by systematically varying the substituents of the zwitterionic group. Radical polymerisation via the RAFT (reversible addition-fragmentation chain transfer) method in trifluoroethanol proceeded smoothly and was well controlled, yielding polymers with predictable molar masses. Molar mass analysis and control of the end-group fidelity were facilitated by end-group labeling with a fluorescent dye. The polymers showed distinct thermo-responsive behaviour of the UCST (upper critical solution temperature) type in an aqueous solution, which could not be simply correlated to their molecular structure via an incremental analysis of the hydrophilic and hydrophobic elements incorporated within them. Increasing the spacer length separating the ammonium and the sulfonate groups of the zwitterion moiety from three to four carbons increased the phase transition temperatures markedly, whereas increasing the length of the spacer separating the ammonium group and the carboxylate ester group on the backbone from two to three carbons provoked the opposite effect. Moreover, the phase transition temperatures of the analogous polyzwitterions decreased in the order dimethylammonio > morpholinio > piperidinio alkanesulfonates. In addition to the basic effect of the polymers' precise molecular structure, the concentration and the molar mass dependence of the phase transition temperatures were studied. Furthermore, we investigated the influence of added low molar mass salts on the aqueous-phase behaviour for sodium chloride and sodium bromide as well as sodium and ammonium sulfate. The strong effects evolved in a complex way with the salt concentration. The strength of these effects depended on the nature of the anion added, increasing in the order sulfate < chloride < bromide, thus following the empirical Hofmeister series. In contrast, no significant differences were observed when changing the cation, i.e. when adding sodium or ammonium sulfate.