Preparation of functionalized core-shell alumina/polystyrene composite nanoparticles, 1 - Encapsulation of alumina via emulsion polymerization

A convenient method for the preparation of well-defined core-shell alumina/polystyrene composite nanoparticles (50 nm) through emulsion polymerization from needle-shaped alumina is reported. The pretreatment of alumina with 3-methacryloxypropyltrimethoxysilane (MPTMS) is essential for successful encapsulation and for creating strong interfacial interaction between alumina and polystyrene (PS). High yield and binding efficiency (both higher than 90%) are achieved by a proper selection of the reaction conditions. As revealed by transmission electron microscopy (TEM) and atomic force microscopy (AFM), an ideal core-shell structure is obtained with one alumina needle as the core and PS as the shell when the amount of alumina is appropriate. However, when more alumina is used, the PS latexes contain an agglomerate of a few alumina needles arranging in a parallel fashion without any precipitation of alumina. The analysis of the grafted and free PS has shown that the grafted PS has bigger molecular weight (MW) and larger molecular weight distribution (MWD) presumably due to some condensation between the methoxyl groups of the silane moiety. The polymerization kinetics and the encapsulation mechanism have also been discussed.