Emulsifier free latices

Emulsifier-free latices are useful not only for industrial purposes but also for studies on colloidal properties (1, 2) and medical applications (3, h). Various methods have been tried to prepare characteristic emulsifier-free latices (5-8). Among them, copolymerization of hydrophobic monomers with hydrophilic comonomers has been the most applicable one (7, 8). There have been many studies on the effects of ionic comonomers on the kinetics of aqueous copolymerization and the properties of the resulting latices, but nonionic hydrophilic comonomers have rarely been used for these purposes. 

Methods. The adsorption was determined by adding a surfactant mixture of known composition to the emulsifier-free latex. The solid/solution ratio was held constant at 0.17 w/w. In this way a series of adsorption measurements was performed with increasing total surfactant concentration. Note that, while the ratio of the two surfactants in such a series is constant in the whole system, it is not necessarily constant on the surface or in the solution because of the preferential adsorption of one of the surfactants. 

Emulsion polymenzaticm without the use of an emulsifier may be achieved even with a monomer with v ter solubility as low as thet of styrene provided one uses an initiator such as potassium persulfate which introduces ionic end groups into the polymer that can stabilize the polymer latex particles produced electrostatically. Emulsifier free emulsion polymerization is advantageous when the object is to obtain a well-characterized model colloid for use in experiments on colloidal stability, etc. Then it is usually desirable that the surfaces of the colloidal particles be clean. When an emulsifier is used in the iH eparation, its removal (e.g., by dialysis) is generally so incomplete that it is simpler to avoid its use in the first place. However, emulsifier-free latexes are necessarily dilute and consequently of little interest for commercial applications. 

Surfactants (emulsifiers of various chemical nature) are usually applied as stabilizers of disperse systems, they are rather stable, poorly destmcted under the influence of natural factors, and contaminate the environment. The principal possibility to synthesize emulsifier-free latexes was shown. In the absence of emulsifier (but in emulsion polymerization conditions) with the usage of persrrlfate-lype irritia-tors (e g., ammonirrm persulfate), the particles of acrylate latexes can be stabilized with ionized endgroups of macromolecules. The ion radicals appearing in... 

Fitch and Tsai describe the preparation of monodisperse, emulsifier-free latexes made from methyl methacrylate and stabilized solely by end-groups [1]. The initiator system was persulfate-bisulfite-iron ((R-3) and (R-4)) and the temperature was always 30 °C. At a constant rate of initiation they found that the number of particles, N, was independent of the initial monomer concentration over the range 0.00380 to 0.0951 molar, while the particle diameter increased from 35.4 to 105.4 nm. In another experiment at a lower R , they obtained a final particle diameter of 172 nm and JV=1.1 X 10 1 , compared to Z)=68.7 nm and JV = 1.8x 10 1 at the same monomer concentration (0.035 M) but higher R,-. They estimated in the former case that each ionic group occupied 24.7 nm at the point when self-stabilization by... 

A detailed analysis of the viscosity of the electrolyte- and emulsifier-free latexes at low electrolyte concentration is possible only if the electrokinetic parameters of the latex are known. These have not yet been determined, but the results can be discussed in terms of the effective volume fraction of polymer Table VI... 

Polymerization, aqueous Vinyl polymerization with water as the medium and with the monomer present within its inherent solubility limit is a process generally called aqueous polymerization. It includes suspension polymerization in an aqueous medium. This procedure is of technical importance in preparing special plastics such as emulsifier-free latex in which the size distribution among the dispersed particles is fairly sharp. 

Figure 13. Gel permeation chromatogram of polystyrene latex, (PL), prepared by emulsifier-free emulsion polymerization at 1 5 °C(in the absence of silica particles).

Materials. The polystyrene latex, with a mean diameter of 0.42 fim, was synthesized by emulsifier-free emulsion polymerization. Potassium persulfate was used as initiator and the surface charge that stabilizes the latex particles thus originates from sulfate radicals. The synthesis was carried out at the Department of Polymer Technology at Abo Akademi, Finland. 

The emulsifier-free emulsion terpolymerization of PEO-MA macromonomer, BA, and acrylic acid (AA) led to the formation of graft copolymers and stable latexes [101]. At the beginning of terpolymerization, the PEO-MA macromonomer polymerized more quickly than BA or AA. Conversion of the macromonomer increased with increasing initiator concentration and with decreasing mo-... 

Vinyl acetate is polymerized in aqueous emulsion and used widely in surface coating and in adhesives. Copolymerized with vinyl esters of branched carboxylic acids and small quantities of acrylic acid, it gives paint latices of excellent performance characteristics. G. C. Vegter found that a coagulum-free latex of very low residual monomer content can be produced from a mixture of an anionic and a nonionic emulsifier according to a specific operating procedure. The freeze/thaw stability of polymeric latices has been investigated by H. Naidus and R. Hanzes. 

High polymer/surfactant weight ratios (up to about 15 1) of polystyrene microlatexes [73] have been produced in microemulsions stabihzed by polymerizable nonionic surfactant by the semi-continuous process. The copolymerization of styrene with the surfactant ensures the long-term stabihty of the latexes. Nanosized PS microlatexes with polymer content (<25 wt%) were also obtained from an emulsifier-free process [74] by the polymerization of styrene with ionic monomer (sodium styrenesulfonate, NaSS), nonionic comonomer (2-hydroxyethylmethacryalte, HEM A), or both. The surfaces of the latex particles were significantly enriched in NaSS and HEMA, providing better stabilization. 

Acrolein-containing latex particles were used for immobilization of proteins. The latex particles were prepared by emulsifier-free polymerization of acrolein and styrene (Table I). Fluorescent latex particles were prepared by mixing fluorescent dyes such as Hostalux KCB (Hoechst) or coumarin-6 into styrene before the emulsion polymerization (Table I). To increase the immunological sensitivity of the protein-conjugated latex particles, a hexyl group was introduced between the latex particle and the protein (Protein-spacer-latex). Proteins such as human serum albumin (HSA), anti-human serum albumin (anti-HSA-IgG), and a fragmented antibody (anti-HSA-... 

The technique involves first producing a seed latex by emulsifier-free emulsion polymerisation. A polystyrene latex of about 1 pva diameter is usually used. The seed particles are initially swollen using a microemulsion of a free radical initiator and a low molecular weight activating solvent , such as dibutyl phthalate, emulsified in water by sonication using sodium dodecyl sulphate as stabiliser. The seed... 

In all such cases the process initiated by persulfate begins in the aqueous phase with the formation of water-soluble, surface-active polymeric radicals which, after growing to a certain critical size, precipitate to form particles subsequent polymerization proceeds mainly within these particles. The higher the solubility of the monomer in water, the more surface-active radicals and therefore primary particles are formed and the higher the stability and the concentration of the latex, A kinetic curve of the emulsifier-free polymerization of ethyl acrylate confirming this scheme is shown by Curve 1 in Fig. 3 (Yeliseyeva and Petrova, 1970). The process... 

Wang X., Zhang Z., Preparation of polystyrene latex particles by gamma-rays-induced emulsifier-free emulsion polymerization, Radiat. Phys. Chem., 2006,75,1001-1005. 

Faridi-Majidi R, Sharifi-Sanjani N (2007) Preparation of magnetic latexes functionalized with chloromethyl groups via emulsifier-free miniemulsion polymerization. J Magn Magn Mater 311 55-58... 

Uses Emulsifier for latexes, acrylic, styrene-acrylic, and vinyl-acrylic emulsion polymerization food pkg. adhesives defoamer in food-con-tact paper coatings Features APE-free... 

For PSA s with the resin-rubber systems, several types of latexes are being used in place of rubber for the waterborne adhesives. Styrene-butadiene (102) latexes and natural rubber latexes (103) have been mentioned in the literature. In addition, waterborne tackifiers (104) have been developed for PSA s. A family of emulsifier-free, high solids, completely freeze-thaw stable tackifying resins was developed by Rohm and Haas. The new products are viscous resins based on the replenishable tail-oil rosin. The... 

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