Facile and Controllable Synthesis of Hybrid Silica Nanoparticles Densely Grafted with poly (ethylene glycol)

In this contribution, we report that mixture of good and poor solvent greatly enhances the grafting density of nanosized silica grafted with poly (ethylene glycol) (PEG) by “grafting to” method. Methoxypolyethylene glycol (MPEG) (molecular weight 750, 2000 and 4000 g mol−1) was modified in a control manner to prepare epoxide terminated PEG (MPEG-EO). The silica nanoparticles (NPs) were modified with N-(2-aminoethy)-3-aminopropylmethyldimethoxysilane (AMDS) through silanization coupling reaction to obtain well defined siloxane structure. MPEG-EO was coupled to modified silica by the reaction of their terminal groups in mixed solvent (n-decane/toluene). The grafting density of MPEG-EO was found to be controlled by the concentration of MPEG-EO and the ratio of n-decane to toluene in grafting system. Based on the thermogravimetric (TGA), the maximum grafting density was found to be about 2.8, 1.47 and 0.76 chains nm−2 for molecular weight of 750, 2000 and 4000, respectively, which is extremely high compared to previous reports. This high grafting density can be explained by the decreased chain dimension of PEG in the presence of poor solvent. The developed method can be applied to other nanoparticles and polymers which can greatly enhance the application of SiO2 nanocomposite.