Synthesis of Vinyl Polymer−Silica Colloidal Nanocomposites via Aqueous Dispersion Polymerization

Abstract

The surfactant-free synthesis of colloidal dispersions of vinyl polymer-silica nanocomposite particles in aqueous media using a batch emulsion polymerization protocol has been previously described [Percy, M. J.; et al. Langmuir 2000, 16, 6913]. In the present work 2-hydroxypropyl methacrylate [HPMA] was copolymerized with 4-vinylpyridine [4VP] using ammonium persulfate in the presence of an ultrafine silica sol. 4VP is used as an auxiliary in these syntheses; the strong interaction of this basic monomer with the acidic surface of the silica particles is essential for successful nanocomposite particle formation. HPMA monomer was selected since it has appreciable water solubility (up to 13% at 20°C), but HPMA homopolymer is water-insoluble. This unusual solubility behavior ensured that these nanocomposite syntheses were conducted under true dispersion polymerization conditions. In view of the success of these syntheses, we conclude that emulsion monomer droplets and micelles are not a prerequisite for the formation of nanocomposite particles. Both thermogravimetric analysis and elemental microanalyses were used to determine the silica contents of the nanocomposite particles, which ranged from 5% to 42% by mass and depended on the proportion of 4VP in the comonomer feed. Under the conditions investigated the minimum amount of 4VP auxiliary required was around 15%. Depending on the synthesis conditions, the mean particle diameter of the HPMA-4VP/SiO2 particles varied from 205 to 330 nm, as judged by disk centrifuge photosedimentometry. Scanning electron microscopy studies of selected nanocomposites indicated that discrete particles were obtained on freeze-drying, partial particle coalescence occurred on drying at ambient temperature, and complete particle coalescence occurred on annealing at 50°C. The transmittance of the annealed films was greater than 80% over the entire visible wavelength range, indicating a high degree of dispersion for the ultrafine silica sol within the film. Aqueous electrophoresis measurements combined with X-ray photoelectron spectroscopy studies indicated that the surface compositions of these HPMA-4VP/SiO 2 particles are silica-rich.

All-Acrylic Film-Forming Colloidal Polymer/Silica Nanocomposite Particles Prepared by Aqueous Emulsion Polymerization

“…10,14,16,18,29,32,39,59,60 In addition, DCP can be used to probe the colloidal stability of particulate dispersions. For example, incipient flocculation induced by either the physical adsorption of silica nanoparticles 9 or the deposition of an ultrathin overlayer of a conducting polymer is readily detected.…”

A mechanistic investigation of Pickering emulsion polymerization

“…15 In their work, the authors used talc, barium sulphate, kaolin clay and aluminium oxide in the suspension polymerization of a variety of monomers. Since then Pickering hetero-phase polymerization has been developed further and now includes mini-emulsion, [16][17][18] dispersion 19,20 and emulsion polymerization processes, [21][22][23][24][25][26][27] using a variety of monomers and with a range of fillers, such as silica, laponite clay, magnetite, titanium dioxide, graphene oxide. 28 One driver for the development of heterogeneous Pickering polymerization processes is that they do not require molecular surfactants, offering a big advantage to the paint industry as surfactant migration often deteriorates the performance of coatings.…”

Controlled preparation of core–shell polystyrene/polypyrrole nanocomposite particles by a swelling–diffusion–interfacial polymerization method

“…Functional composite particles with tailored structures and morphologies have been prepared by various methods with organic or inorganic substrates [1][2][3][4][5][6].…”