Materials Science & Engineering Graduate Program, Koç University, Sarıyer, 34450 Istanbul, Turkey.
J Phys Chem B. 2012 Dec 13;116(49):14510-4. doi: 10.1021/jp310648d. Epub 2012 Dec 4.
Poly(2-alkyl-2-oxazoline)s have recently gained attention in especially biological applications due to their lower critical solution temperature being close to the body temperature and their biocompatibility. The understanding of how cloud point temperature (T(c)) depends on the salt concentration and the molecular mechanisms responsible for such behavior are important to tune T(c) as desired by the applications. In this paper, we report the effect of a series of sodium salts on T(c) of aqueous poly(2-ethyl-2-oxazoline) (PEOX) solutions by dynamic light scattering. PEOX samples having four different molecular weights were investigated, and the results were compared with those of poly(N-isopropylacrylamide) (PNIPAM), the mostly investigated and used thermoresponsive polymer. Kosmotropic anions decreased T(c) linearly while chaotropic anions increased T(c) nonlinearly with salt concentration. The contributions of different mechanisms to T(c) change have been discussed. Our results indicate that the dominant mechanism is the dehydration of PEOX for divalent kosmotropic anions (CO(3)(2-), SO(4)(2-), S(2)O(3)(2-)) and direct binding for chaotropic anions (NO(3)(-), I(-), ClO(4)(-), SCN(-)). For the remaining monovalent kosmotropic anions (H(2)PO(4)(-), F(-), Cl(-), Br(-)), a combination of dehydration and surface tension mechanisms was in effect. The additional contribution of the surface tension mechanism for the monovalent kosmotropic anions was inferred for different molecular weight PEOX samples and also for PNIPAM. With PEOX molecular weight decreasing from 500,000 to 5000 g/mol, T(c) decreased less with salt concentration which was attributed to the contribution of the surface tension mechanism. For PEOX samples, the decrease of T(c) with kosmotropic anion concentration was faster compared to PNIPAM due to differences in their chemical structure. Our results show that the molecular mechanisms of interactions between PEOX chains and specific anions can simply be inferred from determination of T(c) by a common technique-dynamic light scattering.
聚（2-烷基-2-恶唑啉）由于其低临界溶解温度接近体温和生物相容性，最近在生物应用中受到关注。了解浊点温度（T(c)）如何依赖于盐浓度以及导致这种行为的分子机制对于根据应用需求调节 T(c)非常重要。在本文中，我们通过动态光散射报告了一系列钠盐对水相聚（2-乙基-2-恶唑啉）（PEOX）溶液 T(c)的影响。研究了具有四种不同分子量的 PEOX 样品，结果与研究和使用最多的热响应聚合物聚（N-异丙基丙烯酰胺）（PNIPAM）进行了比较。亲水性阴离子使 T(c)线性降低，而亲水性阴离子使 T(c)随盐浓度非线性增加。讨论了不同机制对 T(c)变化的贡献。我们的结果表明，主要机制是二价亲水性阴离子（CO(3)(2-), SO(4)(2-), S(2)O(3)(2-))使 PEOX 脱水，亲水性阴离子（NO(3)(-), I(-), ClO(4)(-), SCN(-))直接结合。对于其余的单价亲水性阴离子（H(2)PO(4)(-), F(-), Cl(-), Br(-)），脱水和表面张力机制同时起作用。对于不同分子量的 PEOX 样品和 PNIPAM，推断出单价亲水性阴离子的表面张力机制的额外贡献。随着 PEOX 分子量从 500,000 降至 5000 g/mol，T(c)随盐浓度的降低而降低较少，这归因于表面张力机制的贡献。对于 PEOX 样品，与 PNIPAM 相比，由于其化学结构的差异，T(c)随亲水性阴离子浓度的降低更快。我们的结果表明，通过动态光散射等常见技术测定 T(c)，可以简单推断出 PEOX 链与特定阴离子相互作用的分子机制。
