Miniemulsion polymerization of styrene using well-defined cationic amphiphilic comblike copolymers as the sole stabilizer
ABSTRACT Well-defined, positively charged, amphiphilic copolymers containing long alkyl side chains were used as stabilizers in the miniemulsion polymerization of styrene. The copolymers were prepared by controlled free-radical copolymerization of styrene and vinyl benzyl chloride using either the reversible addition-fragmentation chain transfer method or TEMPO-mediated polymerization. The benzyl chloride moities were modified by two different long alkyl chain tertiary amines (N,N-dimethyldodecyl amine and N,N-dimethylhexadecyl amine) to yield the amphiphilic copolymers with vinylbenzyl dimethyl alkyl ammonium chloride units. Owing to their high structural quality, only a small amount of these copolymers was required to stabilize the latex particles (0.5–2wt% vs styrene). Moreover, in the absence of any hydrophobic agent, the amphiphilic comblike copolymer preserved the colloidal stability of both the initial liquid miniemulsion and the final latex. Ill-defined, analogous copolymers were synthesized by conventional free-radical polymerization and in comparison, exhibited poor stabilization properties.
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ABSTRACT: Polymeric surfactants were prepared from dextran, a neutral bacterial polysaccharide. Three series of dextran derivatives were studied: neutral dextran derivatives obtained by the attachment of hydrocarbon groups (C6 and phenoxy) to dextran chains, anionic dextran derivatives obtained by further modification of phenoxy-modified dextrans, polylactide grafted dextran copolymers obtained by a well-controlled three-step procedure. Submicronic emulsions (direct or inverse) with a controlled average diameter can be prepared by selecting the operating conditions and the polymeric surfactant used. Polymeric nanoparticles (either bulk polymer or covalent networks swelled by water) were prepared by free-radical miniemulsion polymerization. The surface of the nanoparticles is covered by a physically and/or covalently attached polysaccharide layer. The average size of the latex particles is correlated to that of the initial emulsion droplets provided that the steric stabilization of the initial droplets is enough. The surface coverage of the nanoparticles was investigated and related to the polymerization conditions.Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2008; 331(1):84-90.
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ABSTRACT: Two comb-like amphiphilic copolymers have been prepared via conventional free-radical random copolymerization of stearyl methacrylate (SMA) and 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) with different feed ratios. The resultant copolymers, poly(SMA-co-DMAEMA), were then characterized by 1H NMR and gel permeation chromatography (GPC) measurements. The surface activity of these copolymers in aqueous solution with different pH values was studied by surface tension measurements. Finally, these amphiphilic cationic copolymers were used as polymeric surfactants in the miniemulsion polymerization of styrene. The hydrophobic stearyl side chains of SMA could be strongly adsorbed onto the monomer droplets or propagating particles during the miniemulsion polymerization, while the hydrophilic and protonated PDMAEMA units at low pH media could stabilize the latexes. Moreover, the influences of the composition and amounts of the polymeric surfactants on the kinetics of the miniemulsion polymerization and colloidal stability have been investigated. The reaction rate of miniemulsion polymerization was found to increase with increasing amounts of polymeric surfactants and decrease with the increase of pH values of aqueous solution.Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2010; 360(1):190-197.
- Advanced Materials - ADVAN MATER. 01/2007; 19(24):4420-4425.