核壳型Fe_3O_4@SiO_2磁性纳米粒子表面超支化聚乙烯共价接枝研究

Covalently Grafting Hyperbranched Polyethylenes onto Core-Shell Fe_3O_4@SiO_2 Magnetic Nanoparticles

报道了一种利用超支化聚乙烯(HBPE)对磁性纳米粒子表面进行共价修饰的方法.首先通过反相微乳液法合成表面包覆Si O2的磁性Fe3O4纳米粒子(Fe3O4@Si O2,简记为FS),并利用偶联剂3-丙烯酰基氧基丙基三氯硅烷对其进行改性,然后与α-二亚胺钯催化剂(Pd-diimine,1)反应,获得磁性粒子共价负载型催化剂(FS-Pd);进一步以所得催化剂在0.1 MPa和15℃下催化乙烯聚合,获得一系列表面HBPE共价接枝的磁性复合粒子(FS-HBPE).通过红外光谱(FTIR)、热重分析(TGA)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线衍射(XRD)、氢核磁共振波谱(1H-NMR)和凝胶渗透色谱(GPC)等技术对所得磁性复合粒子的结构和形貌进行了表征,并对其磁性能进行了评价.结果表明:通过表面引发/催化的链"行走"乙烯聚合,可成功实现HBPE在磁性纳米粒子表面共价接枝,通过聚合时间的改变,可对表面HBPE接枝率进行有效调控;所得FS-HBPE复合粒子呈超顺磁特征,借助HBPE的作用,可稳定分散于多个有机溶剂中,同时可实现快速磁控分离.基于上述优点,所得FS-HBPE磁性复合粒子可望用作贵金属催化剂载体,在相关有机反应中获得应用.

A strategy is reported herein to covalently graft hyperbranched polyethylenes （HBPEs） onto magnetic nanoparticles（NPs）. Core-shell Fe3 04@ SiO2 magnetic NPs （FS） were first synthesized via a reverse microemulsion method and then surface modified with a coupling agent, 3-acryloxypropyhrichlorosilane, to render acryloyl-functionalized FS （FS-Acryl）. The resulting FS-Acryl was further reacted with a Pd-diimine catalyst, [ （ ArN·C （Me） -（Me） C = NAr） Pd （ Me ） （ N =--CMe ） ] ·SbF6 - （ 1 ）, to give a FS-supported Pd- diimine catalyst （FS-Pd）. Surface-initiated/catalytic ethylene polymerization was then carried out with the FS- Pd at 0. 1 MPa/15℃ for different periods,finally rendering a series of HBPE-grafted FS hybrids （FS-HBPE）. The structure and morphology of the as-synthesized FS-HBPE were characterized with Fourier-transformed infrared （FTIR） spectroscopy, thermogravimetry analysis （ TGA）, transmission electron microscopy （ TEM ）, scanning electron microscopy （SEM）, wide-angle X-ray diffraction （WAXRD）, proton nuclear magnetic resonance （1H-NMR） and gel permeation chromatography （GPC）, and their magnetic performance was also evaluated. It is well confirmed that HBPE can be successfully grafted onto FS via the surface-initiated/catalytic chain walking ethylene polymerization, with effectively adjustable polymer grafting ratio simply by changing polymerization time. The resulting FS-HBPE is found to be superparamagnetic and can be stably dispersed in a series of organic solvents at room temperature, with excellent magnetic reponse performance. With these advantages,the resulting FS-HBPE nanocomposites could be potentially used as catalyst supports for various organic reactions.