Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA.
Langmuir. 2010 Jun 1;26(11):8787-96. doi: 10.1021/la9045308.
This article reports on the synthesis of a well-defined hydrophilic ABA triblock copolymer composed of a poly(ethylene oxide) (PEO) middle block and thermo- and pH-sensitive outer blocks and the study of sol-gel transitions of its aqueous solutions at various pH values. The doubly responsive linear triblock copolymer, poly(methoxydi(ethylene glycol) methacrylate-co-methacrylic acid)-b-PEO-b-poly(methoxydi(ethylene glycol) methacrylate-co-methacrylic acid) (P(DEGMMA-co-MAA)-b-PEO-b-P(DEGMMA-co-MAA)), was prepared by atom transfer radical polymerization of a mixture of DEGMMA and tert-butyl methacrylate with a molar ratio of 100: 5 from a difunctional PEO macroinitiator and subsequent removal of tert-butyl groups using trifluoroacetic acid. Dynamic light scattering studies showed that the critical micellization temperature (CMT) of this ABA triblock copolymer in a 0.2 wt % aqueous solution was dependent on the solution pH and can be varied in a large temperature range (>20 degrees C). To study the sol-gel transitions, a 12.0 wt % aqueous solution of the triblock copolymer with a pH of 4.89 was made; its pH value can be readily changed and well controlled by the injection of either a 1.0 M HCl or a 1.0 M KOH solution. From rheological measurements, the sol-gel transition temperature (T(sol-gel)) versus pH curve was found to closely trace the CMT versus pH curve, though there was a shift. By cycling the solution pH between 3.2 and 5.4, we showed that the T(sol-gel) at a specific pH was reproducible. Moreover, multiple sol-gel-sol transitions were realized by judiciously controlling the temperature and pH simultaneously, demonstrating the possibility of achieving on-demand sol-gel transitions by using two external stimuli. In addition, the effect of polymer concentration on T(sol-gel) at pH = 4.0 was investigated. The sol-gel transition temperature increased with the decrease of polymer concentration and the critical gelation concentration was found to be between 4 and 6 wt %.
本文报道了一种具有明确亲水性的 ABA 三嵌段共聚物的合成，该共聚物由聚（氧化乙烯）（PEO）中间嵌段和热响应及 pH 响应的外嵌段组成，并研究了其在不同 pH 值下的水溶液的溶胶-凝胶转变。这种双重响应的线性三嵌段共聚物，聚（甲氧基二（乙二醇）甲基丙烯酸酯-co-甲基丙烯酸）-b-PEO-b-聚（甲氧基二（乙二醇）甲基丙烯酸酯-co-甲基丙烯酸）（P（DEGMMA-co-MAA）-b-PEO-b-P（DEGMMA-co-MAA）），是通过将摩尔比为 100:5 的 DEGMMA 和叔丁基甲基丙烯酸酯混合物在双官能 PEO 大分子引发剂上进行原子转移自由基聚合，并使用三氟乙酸除去叔丁基基团制备的。动态光散射研究表明，这种 ABA 三嵌段共聚物在 0.2wt%水溶液中的临界胶束化温度（CMT）依赖于溶液 pH 值，可以在较大的温度范围内（>20°C）变化。为了研究溶胶-凝胶转变，制备了 pH 值为 4.89 的 12.0wt%三嵌段共聚物水溶液；通过注入 1.0M HCl 或 1.0M KOH 溶液，可以很容易地改变和很好地控制其 pH 值。从流变学测量结果可以看出，溶胶-凝胶转变温度（T(sol-gel)）与 pH 值曲线紧密跟踪 CMT 与 pH 值曲线，尽管存在偏移。通过在 3.2 和 5.4 之间循环溶液 pH 值，我们表明在特定 pH 值下的 T(sol-gel)是可重复的。此外，通过同时明智地控制温度和 pH 值，可以实现多次溶胶-凝胶-溶胶转变，这表明通过使用两种外部刺激可以实现按需溶胶-凝胶转变。此外，还研究了聚合物浓度对 pH=4.0 时 T(sol-gel)的影响。溶胶-凝胶转变温度随着聚合物浓度的降低而升高，并且发现临界凝胶化浓度在 4 到 6wt%之间。
