Li Dejin, Dunlap John R, Zhao Bin
Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA.
Langmuir. 2008 Jun 3;24(11):5911-8. doi: 10.1021/la800277j. Epub 2008 May 7.
We report in this article the use of thermosensitive water-dispersible polymer brush-grafted polymeric particles as carriers for Pd nanoparticles for the catalysis of hydrogenation of styrene in an aqueous/organic biphasic system. Thermoresponsive poly(methoxytri(ethylene glycol) methacrylate) brushes were grown from initiator-functionalized core-shell cross-linked poly( t-butyl acrylate) (P tBA) particles via surface-initiated atom-transfer radical polymerization. The t-butyl group of P tBA in the core was removed with trifluoroacetic acid, followed by loading of Pd2+ cations through ion exchange. Pd nanoparticles were prepared by reduction of Pd2+ ions with ethanol at 70 degrees C. Dynamic light scattering studies showed that the Pd nanoparticle-loaded thermosensitive hairy particles in water began to shrink when the temperature was above 30 degrees C. The supported Pd nanoparticles efficiently catalyzed hydrogenation of styrene in an aqueous/octane biphasic system and were reused five times with no changes in the yields in the first three cycles and slight decreases in the fourth and fifth cycles after the same period of time. Kinetics studies showed that the catalytic activity of Pd nanoparticles was modulated by the phase transition of the thermosensitive brush layer, resulting in a non-Arrhenius dependence of apparent initial rate constant, k app, on temperature.
在本文中，我们报道了使用热敏性水分散性聚合物刷接枝的聚合物颗粒作为钯纳米粒子的载体，用于水/有机双相体系中苯乙烯的催化氢化反应。通过表面引发的原子转移自由基聚合反应，在引发剂功能化的核壳交联聚（丙烯酸叔丁酯）（P tBA）颗粒上生长热敏性聚（甲氧基三（乙二醇）甲基丙烯酸酯）刷。用三氟乙酸去除核中P tBA的叔丁基，然后通过离子交换负载Pd2+阳离子。在70℃下用乙醇还原Pd2+离子制备钯纳米粒子。动态光散射研究表明，负载钯纳米粒子的热敏性毛状颗粒在水中温度高于30℃时开始收缩。负载的钯纳米粒子在水/辛烷双相体系中高效催化苯乙烯的氢化反应，可重复使用五次，在前三个循环中产率没有变化，在相同时间段后的第四个和第五个循环中产率略有下降。动力学研究表明，钯纳米粒子的催化活性受热敏刷层的相变调节，导致表观初始速率常数k app对温度呈现非阿累尼乌斯依赖性。
