Non-aqueous Sol-gel Reaction Of Teos And Nano-composite Prepared By In-situ Miniemulsion Polymerization

In recent years, much attention has been paid to the preparations of nano-composites by miniemulsion polymerization, but dispersion of inorganic nano-particles in organic phase is still a rough problem. To avoid the prolem, in this paper, we try to prepare nano-composites by in-situ combining non-aqueous Sol-Gel reaction and miniemulsion polyrization.Firstly, kinetics of non-aqueous Sol-Gel process of tetraethylorthosilicate (TEOS) in carboxylic acids system was investigated by gelation time measuring, dynamic light scattering (DLS) and conductance measuring methods, then the mechanisms were discussed. It is concluded that to obtain spherical silica particles, TEOS molecule should be completely hydrolyzed instantly. Thereafter, a route with formic acid as catalytic system, monomer as dispersing media was determined to prepare nanosized SiO₂ non-aqueous sols. The dependence of stable time of the sol on process parameters was studied. And the transmission electron microscopy (TEM) showed the formation of silica colloidal particles in the sols.Secondly, miniemulsion copolymerization of styrene and acrylate monomer involvingγ—methacryloxypropyltrimethoxysilane (KH-570), with sodium dodecyl sulphate (SDS) as emulsifier and Stearyl acrylate (SA) as co-stabilizer was carried out. Then the dependence of kinetics, latex size and stability on the process parameters was investigated. Results show that, the polymerization rate is mainly affected by KPS concentration, SDS concentration and KH-570 amounts; the latex size is mainly affected by SDS concentration and KH-570 amounts, independent with KPS concentration, which indirectly indicate the dominant droplet nucleation; the stability is related to the condensation reaction derived from the alkoxysilane hydrolysis among particles. Moreover, the mechanical properties of copolymer show that with the increase of KH-570 amounts, the strength and elongation at break of material undergo an increase, followed with a decrease.Ultimately, on the understanding of non-aqueous Sol-gel reaction and miniemulsion polymerization, Polyacrylate/SiO₂ nano-composite was prepared by mixing the initial product of non-aqueous Sol-gel reaction of TEOS and KH-570 with acrylate monomer, followed by miniemulsion polymerization. TEM, Differential scanning calorimetry (DSC), DLS and electronic universal testing machine were employed to characterize the structure and property of the products. Results show that composite latexes with two different structures could be obtained with two different SiO₂ contents. Glass transition temperature (Tg) of the composite is enhanced by increasing SiO₂ content. In addition, the mechanical properties are improved.