Aqueous polymeric latex

The polymerization iavolves the reaction of sodium polysulftde with ethylene dichloride ia aqueous media at 70°C for 2—6 h, yielding an aqueous dispersion (latex) of the polysulftde mbber. 

TA Wheatley, CR Steuernagel. Latex emulsions for controlled drug delivery. In JW McGinity, ed. Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms,... 

In the conventional emulsion polymerization, monomer droplets are dispersed ip an aqueous phase containing micellar aggregates of surfactant. In this case, the dispersed phase represents a relatively small volume fraction of the system and the micellar aggregates constitute the sites of the polymerization process. In the gel(paste)-like emulsions employed here, the volume fraction of the dispersed phase can be as high as 0.99, and the cells of the concentrated emulsion lead to the polymerized latex particles. 

As a result of the advances in catalyst discovery for aqueous ethylene polymerization, silica-polyethylene nancomposites have been prepared with structures that vary with changing catalyst structure and silica composition." It is likely that many more advances in the area of high-tech composites with potential biological and nanotechnology applications will be made in the next few years through aqueous polymerization processes. In addition to free radical polymerizations and catalytic polymerizations, it should be noted that oxidative polymerizations can also be performed in aqueous media to yield conducting polymers. Recently, this has been used to prepare polypyrrole-coated latex particles that are expected to be interesting synthetic mimics for micrometeorites. 

Examples of aqueous coating solutions include water-soluble low molecular weight cellulose ethers, emulsion polymerization latexes of polymethacrylates, and dispersions of water-insoluble polymers such as ethyl-cellulose in the form of pseudolatex. These solvent-free coating solutions provide a range of different coatings... 

As previously mentioned, the properties of olefm-CO copolymers depend strongly on the nature of the olefin employed. The glass transition temperature of 1-olefin-CO copolymers decreases from room temperature to nearly -60 °C upon increasing the chain length of the 1-olefin from propylene to 1-dodecene [33]. By contrast to polar ethylene-CO copolymers, copolymers with higher l-olefins display a hydrophobic character. For 1-olefin copolymerization, catalysts with entirely alkyl-substituted diphosphine hgands R2P-(CH2) -PR2 (R=alkyl, by comparison to R=Ph in dppp) such as 3 are particularly well-suited [48]. Efhylene-l-olefin-CO terpolymers and 1-olefin-CO copolymers can be prepared in aqueous polymerizations [43, 47, 48]. In the aforementioned copolymerization reactions, the polyketone was reported to precipitate during the reaction as a sohd [45, 47, 48, 50]. However, in the presence of an emulsifier such as sodium dodecyl sulfate (SDS) and under otherwise suitable conditions, stable polymer latexes can be obtained. 

In the latter, the undecenoic acid termonomer, with a hydrophilic carboxylic acid moiety, can function as a copolymerizable stabilizer. By comparison to terpo-lymerization in non-aqueous polymerizations in methanol, the high local concentration of the liquid termonomer in droplets in the aqueous polymerization is beneficial for its incorporation. The 1-olefin copolymers exhibit glass transition temperaUires of Tg+10 to -55 °C, and thus can form films upon drying of a latex at room temperature. 

Polymerization in aqueous suspension is by far the most convenient and widely used technique. The monomer is moderately soluble in water, and the pol3uner usually separates as a fine white floe which can be filtered easily and washed. A particular advantage of aqueous polymerization is that one can employ redox initiators such as persulfate-bisulfite r chlorate-sulflte. These catalysts permit rapid polymerization to high conversion at relatively low temperatures, usually 20-40 C. Emulsifying agents may be present, and it is possible to prepare polymer in the form of a stable latex. ... 

Early examples of the precipitation approach include the aqueous solution polymerizations reported by Chaimberg et al. [53] for the graft polymerization of polyvinylpyrrolidone onto silica. The nonporous silica particles were modified with vinyltriethoxysilane in xylene, isolated and dispersed in an aqueous solution of vinylpyrrolidone. The reaction was performed at 70°C and initiated by hydrogen peroxide, after which precipitation on the surface occurred, leading to encapsulation. Nagai et al. [54] in 1989 reported on the aqueous polymerization of the quaternary salt of dimethylaminoethyl methacrylate with lauryl bromide, a surface-active monomer, on silica gel. Although the aim was to polymerize only on the surface, separate latex particles were also formed. 

The conformational entropy of the individual polymer molecules must be maximized. (See Figure 13.6.) For partly polymerized latex particles whose diameter is the same order of magnitude as the end-to-end distance of individual chains ( 500-800 A), the chains will prefer to have loops and ends dangling in the aqueous phase (Sperling et al, 1972), as illustrated in Figure 13.6A. 

Latex la- teks [NS latic. latex, from L. fluid] (1835) (pi lattices or latexes) n. (1) An emulsion of a polymeric substance in an aqueous medium. (2) The sap of the hevea (rubber) tree and other plants, or emulsions prepared from the same. Latices of interest to the coatings and plastics industry are based mainly on styrene-butadiene co-polymers, polystyrene, acrylics, and vinyl polymers and co-polymers. (3) Fine dispersion of rubber or resin, natural or synthetic, in water the synthetic is made by emulsion polymerization. Latex and emulsion are often used synonymously in the paint industry. Emulsified monomers once polymerized become solids or plasticized gel particles and not emulsions but aqueous suspensions. Lovell PA, El-Aasser MS (eds) (1997) Emulsion polymerization and emulsion polymers. John Wiley and Sons, New York. Martens CR (1964) Emulsion and water-soluble paints and coatings. Reinhold Publishing Co., New York. VanderhofF JW, Gurnee EE (1956) Motion picture investigation of polymer latex phenomena. TAPPI 39 (2) 71-77. VanderhofF JW, Tarkowski HL, Jenkins MC, Bradford EG (1966) Theoretical considerations of the interfacial forces involved in the coalescence of latex particles. J Macromol Chem 1 (2) 361-397. 

Another example of the depletion zone relates to the core-shell effects in the synthesis of latexes (63). Consider a partly polymerized latex. The remaining monomer may be the same or different from the already formed polymer. Many such systems have most of the polymer in the interior, and most of the monomer near the surface, because the polymer avoids the aqueous interface. A requirement is that the latex particle be larger than the end-to-end distance of the polymer chains already formed. This requirement is usually met. This has two consequences ... 

Polyvinylchloride, PVC. PVC was commercialized in 1931 when its plasticization was developed. However, owing to the low molecular weight nature of the plasticizers, they tend to migrate to the surface and evaporate, which causes premature brittleness. Over the years, several types of polymeric modifiers were discovered acrylic, elastomeric, chlorinated polyolefins, vinylic, and their copolymers and/or mixtures, e.g., ABS, MBS, SMA. Since most of these materials were polymerized in aqueous media, latex blending was the natural early method. 

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. 

Direct contact of the dispersed SWCNTs and the conductive polymer is favorable, because this presumably decreases the non-contact resistivity between the CNTs by the formation of conductive bridges between adjacent CNTs in the CNT network. The high affinity of conjugated polymers for CNTs through it-it electronic interactions ensures a close conductive polymer-CNT contact. Applying these conductive polymers to a water-based system requires the conductive polymer to have a surfactant-like nature. Water-soluble polythiophenes have been used to disperse SWCNTs in water, but no quantitative information with regard to the level of SWCNT individualization was provided. Polymeric surfactants like poly(styrene sulfonate] (PSS] have been reported to effectively disperse CNTs in water. PSS is also used in the preparation of an aqueous dispersion (latex] of the conductive polymer poly(3,4-... 

Kawaguchi et al. [118] proposed the modification by hydrolysis of the surface groups of mono-disperse acrylamide-styrene copolymer latex obtained by an emulsifier-free aqueous polymerization. In this way they obtained a series of polymer latexes having the same particle size but different kinds and amounts of functional groups on the particles surfaces. 

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