Latex preparation

E. Daniels, E. D. Sudol, and M. S. El-Aasser, eds.. Polymer Latexes Preparation, Characterisation and Applications, ACS Symposium Series, Vol. 492, American Chemical Society, Washington, D.C., 1992. 

Emulsion Polymerization. Poly(vinyl acetate) and poly(vinyl acetate) copolymer latexes prepared in the presence of PVA find wide appHcations in adhesives, paints, textile finishes, and coatings. The emulsions show exceUent stabiHty to mechanical shear as weU as to the addition of electrolytes, and possess exceUent machining characteristics. 

As mentioned previously, the properties of the PVAc latexes prepared in the presence of PVA have something to do with the reaction between PVA and initiators during the polymerization. 

There has been a conventional sense that the PVAc latexes prepared in the presence of PVA as a protective colloid contain the graft copolymer of PVA and PVAc, so that PVAc particles in the dried latex film are not extracted at a high ratio with solvents. In this Chapter, it has been defined without an influence by the usual sense that the porous PVA-PVAc composite can be prepared from the PVAc latex film with acetone extraction. The porous film consists of the spherical cells of PVA... 

To demonstrate film-forming properties of the latex, prepare a drawdown bar by adhering a double thickness of adhesive tape to each end of a glass rod. 

Criticize or defend the following proposition Zeta potentials for three different polystyrene latex preparations were calculated by the Helmholtz-Smoluchowski equation from electrophoresis measurements made in different concentrations of KCl.f... 

To the latex prepared, 7% of styrene are added followed by sodium formaldehyde sulfoxylate dissolved in water and cumene hydroperoxide. An exothermal reaction is observed. 

The isolation of the latex prepared as described before occurs in a spray dryer by atomization in the presence of air as the drying medium. Fumed silica is added by suspending it in the gaseous drying medium. 

A polymer called latex, prepared from a monomer that contains organic groups, is deposited as small spheres (0.1—0.3 pm in diameter) on the support to form a continuous film about 1—2 pm thick. The support is made of silica microspheres or spheres of polystyrene of about 25-50 pm diameter (Fig. 4.4). 

Seven polystyrene latexes prepared with persulfate initiator and bicarbonate buffer were characterized to demonstrate the efficacy of this method (6). Three were monodisperse latexes prepared using conventional emulsifiers four were prepared using sodium styrene sulfonate or sodium vinyltoluene sulfonate as canan-omeric emulsifiers. Each latex was subjected to serum replacement with... 

Table IV shows that dialysis is ineffective in cleaning the latexes for characterization. Earlier work (3,5) also showed that dialysis is ineffective in removing the adsorbed emulsifier and replacing the Na+ and K counterions with H ions. Others have also found that dialysis does not remove emulsifier completely. Brodnyan and Kelley (10) found that aqueous solutions of C14-tagged sodium lauryl sulfate equilibrated upon dialysis, but only 9.5% and 22% of the emulsifier was removed from latexes dialyzed under the same conditions. Matijevic et al. (11) dialyzed a butadiene-styrene copolymer latex prepared using rosin acid soap for 160 days and removed only about 50% of the emulsifier.

The foregoing latexes prepared using persulfate initiator and bicarbonate buffer contained surface sulfate groups and, in some cases, surface hydroxyl groups. None of these latexes contained carboxyl groups. These latexes had final pH values of 7-8. If the bicarbonate buffer was omitted, the final pH of the latex was 2-3 because of the bisulfate ion generated by the persulfate decomposition. 

A polyvinyl acetate latex prepared by semi-continuous polymerization at 55° using a polymethacrylic acid-nonylphenol-poly-ethoxylate phosphate ester emulsifier and sodium persulfate-sodium formaldehyde sulfoxylate initiator (23). The latex was cleaned by ion exchange and serum replacement using both Nuclepore and Pellicon membranes, and the cleaned latex and serum fractions were analyzed by conductometric titration. In addition, the dried films were extracted with water and organic solvents, and the extracts were analyzed by infrared spectroscopy and thermo-gravimetric analysis. 

Procedures. A standard recipe for the latex preparation is shown below (St + M2) 20 g, (water + buffer) 160 g, and initiator 5 mmole/1. The weight fraction of M2 in monomer charge (f) was varied from 0.01 to 0.50. Polymerizations were carried out at 55°C or 70°C and pH 2.5 or 9.0 under nitrogen. Samples were withdrawn from the reaction mixture at various time intervals and the polymer was precipitated in an excess of acetone. The conversion and polymer composition were determined by gravimetric means and by elemental analysis, respectively. The M2 fraction in instantaneously-formed copolymer ( Fi ) was calculated from eq. 1 ... 

I Latex Preparation, In the present work it was found that the largest changes in particle size were obtained by variation of either the styrene concentration, the ratio of alcohol to water or by the choice of alcohol. In Tables I and II it can be seen that increases in either the styrene concentration or the ratio of ethanol to water caused the formation of latex particles of increased particle size. The coefficients of variation for the latices were always less than 10%. 

Latex Preparation Analysis. Deionized water was used for the aqueous phase in the polymerization and commercial grade vinyl chloride monomer (99.9% pure) was used without further purification. The emulsifier was a salt of a sulfated fatty alcohol, and the emulsifier solution for metering was prepared to have 0.15 mol/L in water. The initiator system was a water soluble redox system. 

Formation of solubilized surfactant-latex complexes can influence the properties and performance of vinyl acrylic latexes prepared with NaLS and other penetrating type anionic surfactants. Such complexes seem to affect glass transition temperature and film coalescence process (12). 

The polarity and adsorption data discussed above reveal some interesting aspects of the surface chemistry of vinyl acrylic latex surfaces. It is quite likely that the polarity of the latex films, expecially of the two co-polymers, determined by contact angle measurements may not correspond exactly with their respective latex surfaces in the dispersed state due to reorientation of polymer chains during film formation. But the surfactant adsorption data shows clearly that the three latex surfaces in their dispersed state do exhibit varying polarity paralleling the trend found from contact angle measurements. The result also shows that the surface of the co-polymer latex surface is a mixture of vinyl acetate and acrylate units. This result is somewhat unexpected in a vinyl acrylic latex, prepared by a batch... 

The latexes investigated were the 357 nm Dow monodisperse polystyrene (LS-1010) and two polydisperse polystyrene latexes prepared in our laboratory (2) where the concentration of functional monomer, Cops II (Alcolac-ammonium salt of a short chain vinyl sulfonate), added to the recipe was 10 3 and 10 -M for and C, respectively. 

In Figure 5, the distributions of carboxyl groups given as weight percent based on the amount of MAA charged are presented for the latexes prepared by batch and semi-continuous processes. In this figure, Column 1 represents the amount of carboxyl groups in the serum (see also Table VI), Column 2 represents the value... 

Figure 7 shows the dynamic mechanical response obtained with the latex prepared with a constant monomer feed composition. 

The latexes prepared in the group of Ford [68,69] consisted of hydrophobic monomers and a cross-linker, i.e., styrene, methacrylate monomers with various substitutes in the ester moiety, divinylbenzene, and hydrophilic monomers bearing charged groups, viz., styrylmethyl(trimethyl)ammonium and styrylmethyl(tributyl)ammonium cations. The latexes were catalytically active in reactions of decarboxylation of 6-nitrobenzioxazole-3-carboxylate (Scheme 6) and p-nitrophenyl hexanoate hydrolysis (Scheme 7, n = 6). 

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