Emulsion polymerization formulation components

The physical picture of emulsion polymerization is based on the original qualitative picture of Harkins [1947] and the quantitative treatment of Smith and Ewart [1948] with subsequent contributions by other workers [Blackley, 1975 Casey et al., 1990 Gao and Penlidis, 2002 Gardon, 1977 Gilbert, 1995, 2003 Hawkett et al., 1977 Piirma, 1982 Poehlein, 1986 Ugelstad and Hansen, 1976]. Table 4-1 shows a typical recipe for an emulsion polymerization [Vandenberg and Hulse, 1948]. This formulation, one of the early ones employed for the production of styrene-1,3-butadiene rubber (trade name GR-S), is typical of all emulsion polymerization systems. The main components are the monomer(s), dispersing medium, emulsifier, and water-soluble initiator. The dispersing medium is the liquid, usually water,... 

In vinyl compound polymerization of vinyl acetate, alcohol, bromide, chloride, or carbonate, ascorbic acid can be a component of the polymerization mixture (733-749). Activators for the polymerization have been acriflavine (734), other photosensitive dye compounds (737,738), hydrogen peroxides (740,741,742), potassium peroxydisulfate (743), ferrous sulfate, and acyl sulfonyl peroxides (747). Nagabhooshanam and Santappa (748) reported on dye sensitized photopolymerization of vinyl monomers in the presence of ascorbic acid-sodium hydrogen orthophosphate complex. Another combination is vinyl chloride with cyclo-hexanesulfonyl acetyl peroxide with ascorbic acid, iron sulfate, and an alcohol (749). Use of low temperature conditions in emulsion polymerization, with ascorbic acid, is mentioned (750,751). Clarity of color is important and impact-resistant, clear, moldable polyvinyl chloride can be prepared with ascorbic acid as an acid catalyst (752) in the formulation. 

There are several formulation components that can be present in an emulsion polymer (latex) formulation, which can be added before, during, or after the polymerization reaction. This section is intended to provide the reader with an overview on the role of each component, as well as their in impact the process and/or the product. 

Klein A, Daniels ES. Formulation components. In Lovell PA, El-Aasser MS, editors. Emulsion Polymerization and Emulsion Polymers. England John Wiley Sons 1997. 

The earliest mathematical model of emulsion polymerization was that of Smith and Ewart [1-3], and was based on the Harkins [4-6] mechanistic understanding of emulsion polymerization (see Sections 4.3 and 4.4). This model was applicable only to a batch polymerization in which all formulation components were added at the start of the reaction. Modifications to this basic understanding were made by Gardon [7] in his model. A good review of emulsion polymerization modelling is provided by Penlidis et al. [8]. 

This chapter is intended to give a practitioner of emulsion polymerization an overview and introduction to the components which go into a latex formulation. 

The present review will mainly focus on inverse emulsion polymerization, the most commonly employed water-in-oil synthesis method and on inverse microemulsion polymerization which is more recent and offers some new prospects. The formulation components and their actions, the various structures of the colloidal dispersions prior to polymerization and some latex properties will be discussed. The kinetics and the mechanisms occurring in these water-in-oil systems will also be analysed and compared to the more conventional emulsion polymerization process. 

Various patents and papers report how to improve the performance of poly(vinyl acetate) adhesives. This is generally achieved by using specific functional comonomers in the emulsion polymerization phase, by including polyvalent metal salts in the adhesive formulation, or by post-addition of thermosetting resins such as urea-formaldehyde (UF), melamine-formaldehyde (MF) or polyisocyanates for two-component systems [1-7]. 

Many mixtures of surfactants, especially ionic with nonionic, exhibit surface properties significantly better than do those obtained with either component alone. Such synergistic effects greatly improve many technological applications in areas such as emulsion formulations, emulsion polymerization, surface tension reduction, coating operations, personal care and cosmetics products, pharmaceuticals, and petroleum recovery, to name only a few. The use of mixed surfactant systems should always be considered as a method for obtaining optimal performance in any practical surfactant application. 

Surfactant is another key component in controlling the emulsion polymerization process, which plays an important role in formulating polymers that preserve microstructures of tunable topology and the length scale of the parent microemulsion template. [21]... 

Usually the polymerization solvent is formulated into the resist emulsion, in cases where the polymer is not isolated from solution. In some cases the solvent is partially or wholly removed by ultrafiltering the resist emulsion after formulation. Since ultrafiltration tends to increase manufacturing costs as well as removing small amounts of other resist components, ideally this step is left out. The removal of the polymerization solvent can increase the Tg of the deposited coating, and can therefore have a direct effect on coating conditions (such as voltage, bath temperature and coating time). Typical solvents include 2-methoxy-propanol, 2-methoxyethyl ether, 2-butoxyethanol, 2-propanol and 1,4-dioxane. 

Chem. Desaip. Blend of hydrophobic components and paraffinic hydrocarbons Uses Defoamer for syn. latex, matte aq. coatings, aq. architectural coatings, plasters based on organoslllcate, aq. adhesives, emulsion polymerization Features Retains antIfoamIng props, during paint storage exc. stability effective extreme temp, and pH conditions (to 100 C) silicone-ffee Use Level 0.1-0.4% on total formulation... 

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

Copolymers, as the name implies, are produced from the polymerization of two different materials. Probably one of the most widely used copolymer emulsion adhesives is that based on vinyl acetate ethylenes, commonly referred to as VAEs (see Ethylene vinylacetate copolymers). These are produced by the copolymerization of vinyl acetate and 10-20% ethylene, the resulting polymer base possessing some superior properties over the PVA-based emulsions referred to above. These superior properties relate principally to the increased inherent flexibility of the dry VAE film due to the internal plasticization effect of the ethylene component in the polymer, which enhances adhesion to many difficult surfaces. There are, however, a number of other polymers and copolymers that are used as the formulating basis for alternative specialized emulsion adhesive systems. 

Polymeric surfactants adsorb at solid-liquid interfaces to give enhanced colloidal stability and at liquid-fluid interfaces to control (increase or inhibit) foaming or emulsion stability. The relatively wide molecular weight distribution of most commercial polymeric surfactants means that competitive adsorption processes can affect and be affected by other components in a formulation, as well as the end-use function of the system. With polymers, it often takes patience to know the final effect they produce. 

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