Synthesis and Polymerization Kinetics of Polystyrene Grafting using Azo-groups Bounded SiO2 as an Initiator

This work presents a new method for synthesis of inorganic/organic hybrid nanoparticles via the in-situ polymerization by the use of the azo-groups bounded silica nanoparticles as a radical initiator and styrene as a model vinyl-monomer. The synthesis and the structure of silica/polystyrene (SiO₂/PS), and the polymerization kinetics of the styrene initiated by the azo-groups bounded SiO₂ nanoparticles are studied with techniques such as FTIR, XPS, DSC, GPC, and TEM. Results show that the SiO₂-g-PS nanoparticles are synthesized successfully, and the resulting hybrid nanoparticles have a core-shell structure with SiO₂ in the core and the polystyrene on the outside layer. The percentage of the grafted PS on the SiO₂ surface increases with the progress of the polymerization before 6 h, and the largest amount of the grafted PS reaches 33% of the silica nanoparticles.

Consequently, the size of the nanoparticles increases ca. 20 nm upon the polystyrene grafting. The molecular weight of the grafted PS increases with the polymerization, and it has reached a much large value in the first several polymerization hours while it keeps a constant value approximately in the following polymerization process. Meanwhile, the polydispersity index of the grafted PS gradually increases with the progress of the polymerization. These phenomena agree with the theory of the traditional free radical polymerization very well.