双分布聚乙二醇接枝纳米二氧化硅的高效可控制备

在混合溶剂中通过"grafting to"的方法将2种分子量不同的聚乙二醇单甲醚(MPEG M_w=750,4000)接枝到氨基修饰的St?ber法二氧化硅(SiO_2-NH_2)表面,制备双分布纳米接枝复合物.采用二步法,先将带环氧端基的低分子量聚乙二醇单甲醚(MPEG-EO)与SiO_2-NH_2在甲苯溶剂中充分反应后,与高分子量的MPEG-EO在甲苯和正癸烷的混合溶剂中使用相同的反应条件和后处理方法,能便捷制备出具有双分布接枝的纳米复合物.在接枝反应体系中,分子链的链段尺寸和接枝密度之间存在着密切关系.一定的范围内,接枝密度随链段尺寸减小而增大.通过改变混合溶剂比例来调控接枝链段的尺寸,可以很好控制聚合物的接枝密度.在双分布接枝的纳米复合物中,低分子量的接枝密度为0.85 chains/nm~2,高分子量的接枝密度能达到0.40 chains/nm~2,体现出了简单、高效、可控的特点,与聚环氧乙烷(PEO)共混后分散良好,对于制备出均匀分散的纳米复合材料起到了一定的指导作用.

Efficient and Controllable Synthesis of Grafting Bimodal Polymer Brushes on Nanoparticles

We report here a facile and controllable synthesis of bimodal poly(ethylene glycol) (PEG) brushes grafted on silica nanoparticles (NPs) through mixture of good and poor solvents.Methoxypolyethylene glycol (MPEG) (Mw =750 and 4000) was modified in a control manner to prepare epoxide terminated PEG (MPEG-EO).The silica,with well-defined siloxane structure and modified by amino groups,was prepared through silanization coupling reaction with,N-(2-aminoethy)-3-aminopropylmethyldimethoxysilane (AMDS).A two step method was used to get the bimodal polymer brushes grafted onto the nanoparticles (NPs).MPEG-EO with low molecular weights (Mw =750) was fast coupled to modified silica in toluene at 110 ℃,the obtained sample was again reacted with MPEG-EO with high molecular weight (Mw =4000) in a mixed solvent of n-decane/toluene.Based on the thermogravimetric (TGA) results,more poor solvent (n-decane) in the solvent mixture resulted in a higher grafting density for MPEG-EO.The grafting density could be controlled easily by changing the composition of the mixed solvent,which was different from the traditional ways to control the grafting density through changing temperature,time and concentration of the coupling agent.The grafting density was found to be about 0.85 and 0.4 chains/nm2 for MPEG-EO with molecular weight of 750 and 4000,respectively.These values are extremely high compared to those previously reported.This high grafting density is explained by the decreased chain dimension of PEG in the presence of poor solvent,which lowers the excluded volume interaction and subsequent inter-chain repulsion,allowing a better packing at the silica surface,and the energy barrier of the surface coupling chemistry is effectively overcomed.This technique,efficiently controllable and facile,provides theoretical guidance for the development of silica NPs and may promote tethering polymer to silica NPs based on the connection between the chain dimension and the grafting density.