Yu Xiaoqian, Herberg Artjom, Kuckling Dirk
Paderborn University, Department of Chemistry, Warburger Str. 100, D-33098 Paderborn, Germany.
Polymers (Basel). 2020 Oct 1;12(10):2265. doi: 10.3390/polym12102265.
Micellar catalysts with a switchable core are attractive materials in organic synthesis. However, little is known about the role of the shell forming block on the performance of the catalyst. Thermoresponsive block copolymers based on poly(-isopropylacrylamide--vinyl-4,4-dimethylazlactone) attached to different permanently hydrophilic blocks, namely poly(ethylene glycol), poly(,-dimethylacrylamide), and poly(2,3-dihydroxypropyl acrylate), were successfully synthesized via reversible addition/fragmentation chain transfer radical polymerization (RAFT). Post-polymerization attachment of an amino-functionalized L-prolineamide using the azlactone ring-opening reaction afforded functionalized thermoresponsive block copolymers. Temperature-induced aggregation of the functionalized block copolymers was studied using dynamic light scattering. It was shown that the chemical structure of the permanently hydrophilic block significantly affected the size of the polymer self-assemblies. The functionalized block copolymers were subjected to an aldol reaction between -nitrobenzaldehyde and cyclohexanone in water. Upon temperature-induced aggregation, an increase in conversion was observed. The enantioselectivity of the polymer-bound organocatalyst improved with an increasing hydrophilic/hydrophobic interface as a result of the different stability of the polymer aggregates.
具有可切换核心的胶束催化剂是有机合成中具有吸引力的材料。然而，关于壳形成嵌段对催化剂性能的作用却知之甚少。通过可逆加成/断裂链转移自由基聚合（RAFT）成功合成了基于聚（N-异丙基丙烯酰胺-N-乙烯基-4,4-二甲基氮杂环丁酮）并连接到不同永久亲水性嵌段（即聚乙二醇、聚（N,N-二甲基丙烯酰胺）和聚（2,3-二羟基丙基丙烯酸酯））的热响应性嵌段共聚物。使用氮杂环丁酮开环反应进行后聚合连接氨基官能化的L-脯氨酰胺，得到功能化的热响应性嵌段共聚物。使用动态光散射研究了功能化嵌段共聚物的温度诱导聚集。结果表明，永久亲水性嵌段的化学结构显著影响聚合物自组装体的尺寸。将功能化嵌段共聚物用于水中对硝基苯甲醛和环己酮之间的羟醛反应。在温度诱导聚集时，观察到转化率增加。由于聚合物聚集体的稳定性不同，聚合物负载的有机催化剂的对映选择性随着亲水/疏水界面的增加而提高。
