Polymer/silica nanocomposite particles

Percy and coworkers [39,40] synthesized colloidal dispersions of polymer-silica nanocomposite particles by homopolymerizing 4-vinylpyridine or copolymerizing 4-vinylpyridine with either methyl methacrylate, styrene, n-butyl acrylate or n-butyl methacrylate in the presence of fine-particle silica sols using a free-radical in aqueous media at 60°C. No surfactants were used and a strong acid-based interaction was assumed to be a prerequisite for nanocomposite formation. The nanocomposite particles had comparatively narrow size distributions with mean particle diameters of 150-250 nm and silica contents between 8 and 54 wt.%. The colloidal dispersions were stable at solids contents above 20 wt.%. 

Figure 4.31 Typical bright-field (a,c) and en-ergy-filtered (25 eV b,c) transmission electron micrographs obtained for the polymer/ silica nanocomposite particles (scale bar 100 nm). The top images show a core-sheir -type morphology for polystyrene/silica...

Since the late 1980s several innovative syntheses of polypyrroles have been discovered. The photosensitized polymerization of pyrrole in aqueous solution and in polymer matrices using tris(2,2 -bipyridine)ruthenium(II) as a photosensitizer has been reported <89CC132>, and PPy can be photochemically deposited on to any type of surface under visible light irradiation conditions <89CC657, 90CC387). The preparation and potential applications of surface-functionalized polypyrrole-silica nanocomposite particles have been discussed <94PP217>. 

Qi DM, Bao YZ, Weng ZX et al (2006) Preparation of acrylate polymer/sihca nanocomposite particles with high silica encapsulation efficiency via miniemulsion polymerization. Polymer 47 4622-4629... 

Contrary to the majority of papers on polymer-silica nanocomposites, the very low content of 3D nanosilica particles in the polymer matrix in this work resulted in average inter-particle distance L larger by an order of magnitude than the radius of gyration Rq of PHEMA. In spite of that, a considerable impact of small 3D silica additives on matrix dynamics was found due to double PU/PHEMA and silica/matrix hybridization. 

By this method also, polymer/silica nanocomposites have been fabricated [165,166]. Merkel et al. discovered that the addition of nanometer-sized fumed silica particles to certain high-free volume, glassy polymers could systematically increase gas permeability. Such high-permeability polymers included poly(4-methyl-2-pentyne) (PMP), poly[l-(trimethyl-silyl)-l-propyne] (PTMSP), andpoly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene) [107]. 

Figure 16.17 shows the formation of conductive polymer/inor-ganic oxide nanocomposite particles. Silica, having a particle size of 20 nm, was dispersed in water, oxidant was added, followed by addition of monomer (pyrrole or aniline), and polymerization was conducted under constant stirring for 16 h at room temperature. Raspberry clusters of nanocomposite were ob-tained. ... 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Tanahashi, M., Hirose, M., Lee, J. C., and Takeda, K. 2006. Organic/inorganic nanocomposites prepared by mechanical smashing of agglomerated silica ultrafine particles in molten thermoplastic resin. Polymer Advance Technology 17 981-990. 

Based on this same general idea, colloidal dispersions of nanocomposite particles made from silica cores and polymeric overlayers have been successfully prepared using appropriate cationic radical initiators, as described in a recent Japanese patent [100]. Recently, Luna-Xavier et al. also demonstrated the successful formation of nanosize siHca/PMMA composite colloids using AIB A as cationic initiator and a nonionic polyoxyethylenic surfactant (NP30) [63,91,101]. Composite particles made from silica beads surrounded by small heterocoagulated PMMA latexes or a thin polymer layer were produced, depending on the size of the silica beads (Fig. 4.11). 

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