Nanocomposites Prepared In-situ Miniemulsion Polymerization With Non-aqueous Silica Sol

Recently, much attention has been paid to the preparations of polymer/inorganicnano-composites by miniemulsion polymerization, but dispersion of inorganicnano-particles in organic phase is still a rough problem. To avoid this prolem, in thispaper, we prepared poly （styrene-acrylate）/SiO₂nanocomposite materials by in-situcombining non-aqueous sol-gel reaction and miniemulsion polyrization.In this paper, miniemulsion polymerization of styrene-acrylate was prepared byusing polydimethylsiloxane （PDMS） as co-stabilizer, sodium dodecyl sulfate （SDS） asemulsifier and potassium persulfate （KPS） as initiator. The particle size and particlesize distribution of latexes were characterized by dynamic light scattering （DLS）. Theresults demonstrated that: the number of latex particles （here latex particles was sitesof miniemulsion polymerization） is independent on the the content of KPS. So withthe amount of KPS increasing, the number of free radiclas and the average number offree radicals in latex particles increases. This leads to the polymerization rate of thissystem increases. The coalscence between latex particles is gradually reduced byincreasing the SDS concentration. In other words, the number of stable place ofpolymerization adds, so that the polymerization rate increases with the increasingSDS concentration. The polymerization rate is lightly affected by co-stabilizer PDMScontent within the appropriate range.Then, SiO₂was prepared by non-aqueous sol-gel reaction of tetraethylorthosilicatand PDMS was used as the modifier of SiO₂. Finally, PDMS modified SiO₂wasdispersed into monomers and poly （styrene-acrylate）/SiO₂nanocomposite materialswere synthesized by miniemulsion polymerization. Dynamic light scattering （DLS）,mechanical property analysis, differential scanning calorimetry （DSC） andtransmission electron microscopy （TEM） were employed to characterize the products.The results show that, introducing silica sol reduces the homogeneity of monomersdroplets and the stability of the dispersed droplets, so that with increasing the contentsof silica sol, the particle sizes increases and the particle size distribution becomeswider. The latex particle morphologies of the nanocomposites were the struture ofseveral silica microdomains encapsulated by polyacrylate. The glass transitiontemperature （Tg） of the composite materials increases with the content of silica increases. The break stress and yield stress of compiste material are improved by theintroduction of silica.