School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, PR China.
J Phys Chem B. 2012 May 10;116(18):5527-36. doi: 10.1021/jp3004322. Epub 2012 Apr 26.
Comprehensive investigations of the effects of species and concentrations of metal ions on the ion-responsive behaviors of poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-B18C6Am)) are systematically carried out with a series of P(NIPAM-co-B18C6Am) linear copolymers and cross-linked hydrogels containing different crown ether contents. The results show that when the B18C6Am receptors form stable B18C6Am/M(n+) host-guest complexes with special ions (M(n+)), such as K(+), Sr(2+), Ba(2+), Hg(2+), and Pb(2+), the LCST of P(NIPAM-co-B18C6Am) increases due to the repulsion among charged B18C6Am/M(n+) complex groups and the enhancement of hydrophilicity, and the order of the shift degree of LCST of P(NIPAM-co-B18C6Am) is Pb(2+) > Ba(2+) > Sr(2+) > Hg(2+) > K(+). With increasing the content of pendent crown ether groups, the LCST shift degree increases first and then stays unchanged when the B18C6Am content is higher than 20 mol %. Remarkably, it is found for the first time that there exists an optimal ion-responsive concentration for the P(NIPAM-co-B18C6Am) linear copolymer and cross-linked hydrogel in response to special metal ions, at which concentration the P(NIPAM-co-B18C6Am) exhibits the most significant ion-responsivity either in the form of linear copolymers or cross-linked hydrogels. With an increase of the content of crown ether groups, the value of corresponding optimal ion-responsive concentration increases. Interestingly, there exists an optimal molar ratio of metal ion to crown ether for the P(NIPAM-co-B18C6Am) copolymer in response to Pb(2+), which is around 4.5 (mol/mol). If the ion concentration is too high, the ion-responsive behaviors of P(NIPAM-co-B18C6Am) may even become surprisingly unobvious. Therefore, to achieve satisfactory ion-responsive characteristics of P(NIPAM-co-B18C6Am)-based materials, both the operation temperature and the ion concentration should be optimized for the specific ion species. The results in this study provide valuable guidance for designing and applying P(NIPAM-co-B18C6Am)-based ion-responsive materials in various applications.
系统研究了不同冠醚含量的聚（N-异丙基丙烯酰胺-共-苯并-18-冠-6-丙烯酰胺）（P（NIPAM-co-B18C6Am））线性共聚物和交联水凝胶中金属离子种类和浓度对离子响应行为的影响。结果表明，当 B18C6Am 受体与特定离子（M(n+)）形成稳定的 B18C6Am/M(n+)主客体配合物时，如 K(+)、Sr(2+)、Ba(2+)、Hg(2+)和 Pb(2+)，由于带电荷的 B18C6Am/M(n+)配合基团之间的排斥以及亲水性的增强，P（NIPAM-co-B18C6Am）的 LCST 升高，并且 P（NIPAM-co-B18C6Am）的 LCST 位移程度的顺序为 Pb(2+) > Ba(2+) > Sr(2+) > Hg(2+) > K(+)。随着侧基冠醚含量的增加，当 B18C6Am 含量高于 20mol%时，LCST 位移程度先增加后保持不变。值得注意的是，首次发现 P（NIPAM-co-B18C6Am）线性共聚物和交联水凝胶对特定金属离子存在最佳离子响应浓度，在此浓度下，P（NIPAM-co-B18C6Am）以线性共聚物或交联水凝胶的形式表现出最显著的离子响应性。随着冠醚基团含量的增加，相应的最佳离子响应浓度值增加。有趣的是，对于 P（NIPAM-co-B18C6Am）共聚物响应 Pb(2+)，存在一个最佳的金属离子与冠醚摩尔比，约为 4.5（mol/mol）。如果离子浓度过高，P（NIPAM-co-B18C6Am）的离子响应行为甚至可能变得不明显。因此，为了获得令人满意的基于 P（NIPAM-co-B18C6Am）的材料的离子响应特性，对于特定的离子种类，应优化操作温度和离子浓度。本研究的结果为设计和应用基于 P（NIPAM-co-B18C6Am）的离子响应材料提供了有价值的指导，以满足各种应用的需求。
