Vinyl anionic surfactants

Three generations of latices as characterized by the type of surfactant used in manufacture have been defined (53). The first generation includes latices made with conventional (/) anionic surfactants like fatty acid soaps, alkyl carboxylates, alkyl sulfates, and alkyl sulfonates (54) (2) nonionic surfactants like poly(ethylene oxide) or poly(vinyl alcohol) used to improve freeze—thaw and shear stabiUty and (J) cationic surfactants like amines, nitriles, and other nitrogen bases, rarely used because of incompatibiUty problems. Portiand cement latex modifiers are one example where cationic surfactants are used. Anionic surfactants yield smaller particles than nonionic surfactants (55). Often a combination of anionic surfactants or anionic and nonionic surfactants are used to provide improved stabiUty. The stabilizing abiUty of anionic fatty acid soaps diminishes at lower pH as the soaps revert to their acids. First-generation latices also suffer from the presence of soap on the polymer particles at the end of the polymerization. Steam and vacuum stripping methods are often used to remove the soap and unreacted monomer from the final product (56). 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

A fluid loss additive for hard brine environments has been developed [1685], which consists of hydrocarbon, an anionic surfactant, an alcohol, a sulfonated asphalt, a biopolymer, and optionally an organophilic clay, a copolymer of N-vinyl-2-pyrrolidone and sodium-2-acrylamido-2-methylpropane sulfonate. Methylene-bis-acrylamide can be used as a crosslinker [1398]. Crosslinking imparts thermal stability and resistance to alkaline hydrolysis. 

Recent investigations have shown that the behavior and interactions of surfactants in a polyvinyl acetate latex are quite different and complex compared to that in a polystyrene latex (1, 2). Surfactant adsorption at the fairly polar vinyl acetate latex surface is generally weak (3,4) and at times shows a complex adsorption isotherm (2). Earlier work (5,6) has also shown that anionic surfactants adsorb on polyvinyl acetate, then slowly penetrate into the particle leading to the formation of a poly-electroyte type solubilized polymer-surfactant complex. Such a solubilization process is generally accompanied by an increase in viscosity. The first objective of this work is to better under-stand the effects of type and structure of surfactants on the solubilization phenomena in vinyl acetate and vinyl acetate-butyl acrylate copolymer latexes. 

ANIONIC SURFACTANTS STUDIED IN VINYL ACRYLIC LATEXES 07)... 

Latex thickening in the presence of penetrating type anionic surfactants such as NaLS appears to depend on polymer composition as seen in Table III. The extent of latex thickening in the presence of excess NaLS decreases with the VA content of a vinyl acetate-butyl acrylate copolymer. Polystyrene and poly acrylate copolymer latexes do not show any thickening. 

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). 

Our results on the interactions of anionic surfactants in vinyl acrylic latexes can be summarized as follows ... 

Lower molecular weight (300-800) anionic surfactants such as NaLS and Alipal EP-110 adsorb at a vinyl acrylic latex in a complex C-type adsorption isotherm, leading to penetration and solubilization of latex. 

Alternative processes include the vinyl esters cf "Versatic acid" (shell Chemicals), with vinyl acetate and acrylamide (49 49 2), which are added gradually after conversion to a pre-emulsion, to an anionic surfactant solution containing a persulfate. Transt parent waterproof films are formed. 

In most cases, a mixture of a polymeric stabiliser such as poly(vinyl alcohol) or Pluronic (an A-B-A block copolymer of PEO, A and PPO) with an anionic surfactant, such as sodium dodecyl sulphate is used. In this case, the stabiHsing mechanism is the combination of electrostatic and steric mechanism, referred to as electrosteric. 

When a relatively water-insoluble vinyl monomer, such as styrene, is emulsified in water with the aid of an anionic surfactant and adequate agitation, three phases result (see Fig. 6.14) (1) an aqueous phase in which small amounts... 

The emulsion polymerization of vinyl acetate may be unique among polymerization processes in that true latices have been formed with anionic surfactants, cationic surfactants, nonionic surfactants, or protective colloids, and with combinations of two or more such reagents, as well as without any added emulsifier. 

Nonionic surfactants such as polyoxyethylated fatty alcohols (such as Emul-phor ON-870 from GAP), alkyl phenyl polyethylene glycol ethers (such as the Tergitols from Union Carbide) and polyoxyethylated octylphenol may be used as protective colloids along with anionic surfactants or, in some cases, as emulsifiers in their own right. The block copolymers of polyoxyethylene and polyoxypropylene (Pluronics) solubilized vinyl acetate. Polymerization takes place at the interface of the surfactant-monomer droplet and the aqueous phase [151]. 

Most commonly, in the emulsion polymerization of vinyl acetate, anionic surfactants are used either alone or in combination with a protective colloid. Typical examples of surfactants which have found application are Aerosol OT (sodium dioctylsulfosuccinate), alkyl aryl sulfonate salts (e.g., Santomerse-3), sodium lauiyl sulfate, etc. A study of the kinetics of the vinyl acetate polymerization in the presence of sodium lauryl sulfate indicated that the rate of polymerization was proportional to the square root of the initiator concentration and the 0.25th power of the number of particles. The number of particles were proportional to the 0.5th 0.05 power of the surfactant concentration but independent of the level of potassium persulfate. The intrinsic viscosity of the final polymer was said to be independent of the initiator concentration and of the munber of polymer particles. These observations were said to suggest that the mechanism of the vinyl acetate polymerization in emulsion resembles that of vinyl chloride [153]. 

Cationic surfactants, in contrast to anionic surfactants, usually reduce both the number of particles involved in the polymerization and the rate of polymerization. The nature of the stabilizing emulsifier has a marked effect on the polymerization kinetics. For example, addition of a non-ionic stabilizer [e.g., poly(vinyl alcohol), a block copolymer of carbowax 6000 and vinyl acetate, or ethylene oxide-alkyl phenol condensates] to a seed polymer stabilized by an anionic surfactant decreased the rate of polymerization to 25% of the original rate. The effect was as if the nonionic stabilizer (or protective colloid) acted as a barrier around the seed particles to alter the over-all kinetics. It may be that the viscosity of the medium in the neighborhood of the nonionic surfactant coating of the polymer particle is sufficiently different from that of an anionic layer to interfere with the diffusion of monomer or free radicals. There may also be a change in the chain-transfer characteristics of the system [156]. 

In equipment similar to that used in Procedure 5-3 with provisions for maintaining a nitrogen atmosphere in the system, 210.75 gm of deionized water, 0.75 gm of Tergitol-7 (sodium heptadecyl sulfate, an anionic surfactant from Union Carbide), 12.5 gm of Cellosize WP-09 (a protective colloid from Union Carbide) and 1 gm of potassium persulfate is blended under nitrogen with agitation. Then 25 gm of vinyl acetate is added and the mixture is heated to 70°C. When the polymerization has started, with stirring, over a 2- to 3-hr period, 250 gm of vinyl acetate is added. The temperature is maintained at 70°-80°C. After the addition has been completed, heating at 70°-80°C is continued for an additional 30 min. The residual monomer content of this latex is less than l . ... 

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