Emulsion polymerization synthesize emulsifier

MAIs may also be formed free radically when all azo sites are identical and have, therefore, the same reactivity. In this case the reaction with monomer A will be interrupted prior to the complete decomposition of all azo groups. So, Dicke and Heitz [49] partially decomposed poly(azoester)s in the presence of acrylamide. The reaction time was adjusted to a 37% decomposition of the azo groups. Surface active MAIs (M, > 10 ) consisting of hydrophobic poly(azoester) and hydrophilic poly(acrylamide) blocks were obtained (see Scheme 22) These were used for emulsion polymerization of vinyl acetate—in the polymerization they act simultaneously as emulsifiers (surface activity) and initiators (azo groups). Thus, a ternary block copolymer was synthesized fairly elegantly. 

Materials. The polystyrene latex, with a mean diameter of 0.42 fim, was synthesized by emulsifier-free emulsion polymerization. Potassium persulfate was used as initiator and the surface charge that stabilizes the latex particles thus originates from sulfate radicals. The synthesis was carried out at the Department of Polymer Technology at Abo Akademi, Finland. 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

An emulsion route can also be used to make nanocomposites with some polymers. Thus well-dispersed (exfoliated) PMMA nanocomposites have been synthesized via emulsion polymerization of MMA in a suspension of MMT (unmodified) or MMT modified with 2,2 -azobis(2-methyl propiona-mide), using sodium lauryl sulfate as the emulsifier and potassium persulfate as the initiator [232]. 

Polymerizations performed with an emulsifier above its critical micelle concentration with all the monomer solubilized within the micelles and without any monomer present as emulsion droplets may be described as micellar polymerizations [62]. Although such systems can never produce a high yield of polymer per unit volume they are advantageous if it is desired to use photochemical initiation, these being transparent whereas emulsions are opaque. Micellar polymerizations can help to elucidate the mechanism of emulsion polymerizations. They are useful practically when it is desired to copolymerize hydrophilic and hydrophobic monomers to synthesize associative thickeners [63,64]. 

Latexes can be synthesized by emulsion pol5mierization. Originally this meant emulsifying an aqueous-insoluble monomer in water with a surfactant and then using a water-soluble free radical initiator to cause polymerization. The term emulsion polymerization is still used, despite the fact that an emulsion is not alwa needed to produce polymer colloids. 

In the semicontinuous process, the reactor is initially charged with a fraction of the formulation (monomers, emulsifiers, initiator and water). The initial charge is polymerized in batch for some time and then the rest of the formulation is added over a certain period of time (typically 3—4 h). The monomers can be fed either as an aqueous pre-emulsion sta-bihzed with some emulsifier or as neat monomers. Monomers contain inhibitors to allow safe storage and they are used without purification. The initiator is fed in a separate stream. The goal of the batch polymerization of the initial charge is to nucleate the desired number of polymer particles. Because particle nucleation is prone to suffer run-to-run irreprodu-cibility, seeded semicontinuous emulsion polymerization is often used to overcome this problem. In this process, the initial charge contains a previously synthesized latex (seed) and eventually a fraction of the formulation (monomers, emulsifiers, initiator and water). Therefore, nucleation of new particles is minimized leading to better reproducibility. 

Surfactants (emulsifiers of various chemical nature) are usually applied as stabilizers of disperse systems, they are rather stable, poorly destmcted under the influence of natural factors, and contaminate the environment. The principal possibility to synthesize emulsifier-free latexes was shown. In the absence of emulsifier (but in emulsion polymerization conditions) with the usage of persrrlfate-lype irritia-tors (e g., ammonirrm persulfate), the particles of acrylate latexes can be stabilized with ionized endgroups of macromolecules. The ion radicals appearing in... 

In order to synthesize an interfacial polyelectrolyte the ionizable groups must be chemically bound to the interface and be an integral part of the polymer molecules comprising the colloidal particles. It is preferable to avoid adsorbed emulsifier, which is usually employed to stabilize these colloids, as it complicates the subsequent purification and quantitative surface characterization of the system. Thus the classical technique of emulsion polymerization, as described by Harkins [2], is not applicable. The systems are actually simpler, employing only monomer(s), water and initiator. It is most important that the initiator be very soluble in the water and that it form ionizable free radicals. The monomer must have a finite solubility in water, although this may be very small (even styrene satisfies this requirement at 0.038 wt.%), but may be present in amounts far in excess of this as an initially separate phase. Initiation of polymerization must then occur in the aqueous solution. For instance, if the initiator is potassium persulfate, K2S2O8, free radical-ions are formed (along with some OH) by the thermal decomposition of the anion ... 

Several water-based alternatives have been reported. Numerous papers describe the synthesis of aqueous emulsions of conductive polymers. Such products can be prepared by the emulsion polymerization of monomers such as pyrrole [20] or aniline [21]. A conductive polymer can also be synthesized on the surface of a polymeric emulsified particle [22]. Such aqueous emulsions can be applied to textiles to produce the desired conductive composite structure. 

Castor oil has found application in the synthesis of interpenetrating polymer networks (IPNs). These materials can be defined as a combination of two polymer networks, at least one of which is synthesized and/or cross-linked in the immediate presence of the other. They are called semi-lPN if just one of the polymers is a network (Athawale et al, 2003). Early reports on castor oil IPNs appeared in 1977 by Yenwo and co-workers. The report discussed the synthesis possibilities via cross-linking of double bonds with sulfur, reaction of hydroxyl groups with diisocyanates, and emulsion polymerizations with saponified ricinoleic acids as emulsifier. Moreover, the IPNs from acrylic polymers, such as polymethyl methacrylate and poly-2-ethoxyethyl methacrylate, and castor oil-based polyurethanes were reported to contribute to the final properties of the material (Cunha et al., 2004 Sanmathi et al, 2004). Incorporation of acrylic moieties into the PU networks increased toughness and thermal properties. In contrast, IPN polyesters derived from castor oil and dibasic acids (e.g. malonic, succinic, glutaric, adipic, suberic, and sebacic acid) were obtained as soft and opaque elastomers (Suthar et al, 2003). 

Despite the considerable number of studies concerned with the preparation of various types of polymer-silicate nanocomposites by the conventional emulsion technique, there has been no report on syntheses of novel polymer-silicate nanocomposites by the emulsifier-free emulsion method. The advantage of this method of polymerization is that a high concentration of surfactant/ emulsifier is considered to be one of the main drawbacks of emulsion polymerization due to difficulties in removing the residual emulsifier from the nanoparticle surface.The recently developed unconventional emulsifier-free emulsion polymerization enables the latter problem to be resolved and composite nanoparticles with tailored morphology to be synthesized. 

The present review of nanocomposites synthesized by in situ polymerization highlights an increasing number of studies on emulsifier-free emulsion polymerization. In our laboratory, using the in situ emulsifier-free emulsion technique, we have prepared a number of polymer nanoparticles and nanocomposites, such as PMMA and PAN nanoparticles, PEHA-SS nanocomposite used for biodegradable superabsorbents, pressure-sensitive adhesives (PSAs), PMMA-MMT, PBA SS, PBMA SS-Mg(OH)2 nanocomposites used for fire retardants, PAN SS used as a water absorbent, poly(EHA-co-AA)-SS nanocomposite to act as a PSA in transdermal drug delivery (TDD) and poly(AA-co-AM)-MBA nanohydrogel for colon-specific drug delivery. ... 

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