Emulsion polymerization with nonionic emulsifiers

Uses Emulsifier for emulsion polymerization, esp. for acrylate homo- and copolymers, vinyl acetate-acrylate copolymers, styrene-acrylate copolymers coemulsifier with nonionic emulsifiers Regulatory BGA XIV, XXXIV... 

Medvedev et al. [57] extensively studied the use of nonionic emulsifiers in emulsion polymerization. The emulsion polymerizations in the presence of nonionic emulsifiers exhibited some differences relative to those carried out with the ionic ones. Medvedev et al, [57] proposed that the size of latex particles remained constant during the reaction period, but their number increased continually with the increasing monomer conversion. The use of nonionic emulsifiers in emulsion polymerization usually results in larger sizes relative to those obtained by the ionic emulsifiers. It is possible to reach a final size value of 250 nm by the use of nonionic emulsifiers in the emulsion polymerization of styrene [58]. 

The emulsifier provides sites for the particle nucleation and stabilizes growing or the final polymer particles. Even though conventional emulsifiers (anionic, cationic, and nonionic) are commonly used in emulsion polymerization, other non-conventional ones are also used they include reactive emulsifiers and amphiphilic macromonomers. Reactive emulsifiers and macromonomers, which are surface active emulsifiers with an unsaturated group, are chemically bound to the surface of polymer particles. This strongly reduces the critical amount of emulsifier needed for stabilization of polymer particles, desorption of emulsifier from particles, formation of distinct emulsifier domains during film formation, and water sensitivity of the latex film. 

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. 

There are an enormous variety of commercial emulsifiers that are employed in emulsion polymerization. Emulsifiers are generally categorized into four major classes anionic, cationic, nonionic and zwitterionic (amphoteric). The anionic and nonionic emulsifiers are the most widely used. In addition, mixtures of emulsifiers are also often used. Since the effects of the molecular structme and chemical and physical properties of an emulsifier on particle formation are still far from being well understood, numerous experimental investigations on particle formation have been carried out to date with various nonionic emulsifiers [99-102], mixed emulsifiers (ionic and nonionic emulsifiers) [18,103-106] and reactive surfactants [33, 107-110]. Recently, polymeric surfactants have become widely used and studied in emulsion polymerizations [111-116]. A general review of polymeric surfactants was published in 1992 by Piirma [117]. Recently, emulsion polymerization stabilized by nonionic and mixed (ionic and nonionic) emulsifiers was reviewed by Capek [118]. 

Nonionic surfactants were developed subsequent to the ionic types and are not normally used as the sole emulsifying agent in emulsion polymerizations. Consequently, the characteristics of emulsion polymerizations using only nonionic emulsifiers have received little attention apart from a series of papers from Medvedev s group in the Soviet Union, although an understanding of these is a prerequisite for the interpretation of their action in combination with ionic emulsifiers. The Bobalek Williams recipe produces... 

Okamura et al, (29) studied the y-induced emulsion polymerization of styrene, methyl methacrylate (MMA), and vinyl acetate with anionic, nonionic, and cationic emulsifying agents and dose rates of 270 to 2 X 10 rad per hour. The over-all reaction rate increased with increasing emulsifier concentration, but depended highly on the kind of emulsifying agent. In the case of MMA, the over-all reaction rate increased with (I = intensity or dose rate). 

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. 

In practice, two types of emulsifiers are used (1) ABA triblock copolymers (e.g., Hypermer B246, HLB = 6 and B261, HLB = 8, IQ), where A is a polyester derived from 12-hydiostearic acid and B is a polyoxyethylene and (2) nonionic emulsifiers such as fatty acid esters of sorbitan and polyoxyethylene derivatives. Note also that the amount of surfactant is higher than that employed in conventional emulsion polymerization, in connection with the stability problems discussed above it lies within 2-5 wt% of the total mass. 

Classification Linear alcohol ethoxylate Definition PEG ether of a mixt. of syn. C9-11 fatty alcohols with avg. 3 moles EO Properties Nonionic Toxicology TSCA listed Uses Surfactant emulsifier in cosmetics intermediate dispersant wetting agent for household/industrial detergents, cosmetics, textiles, leather, agric., paints/coatings, emulsion polymerization, lubricants, silicon and wax emulsions, metal treatment, paper processing... 

Properties M.w. 600 sol. in water, ethanol, toluene misc. with fats, fatty alcohols, and hot min., nat. and syn. oils nonionic Toxicology LD50 (oral, mouse) 1170 mg/kg, (IV, mouse) 125 mg/kg TSCA listed Uses Emulsifier, wetting agent, detergent, dispersant for maintenance and institutional cleaners, textiles, paper, paints, emulsion polymerization solvent pharmaceutic aid (surfactant) spermicide penetrant coupling agent in food-contact textiles antistat in food-pkg. materials... 

Classification Ethoxylated alkyl phenol Formula C9Hi9C6H4(OCH2CH2)nOH, avg. n = 120 Properties Nonionic Toxicology TSCA listed Uses Surfactant), emulsifier for emulsion polymerization emulsifier, cleansing agent in cosmetics in paper/paperboard in contact with dry food... 

Synonyms POE (60) hydrogenated castor oil Definition PEG deriv. of hydrogenated castor oil with avg. 60 moles of EO Properties Nonionic Toxicology TSCA listed Uses Surfactant, solubilizer, emulsifier, emollient for cosmetics, pharmaceuticals, textiles, metalworking, emulsion polymerization, agric., household detergents solubilizer for oil-sol. vitamins in food-contact textiles... 

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