Emulsion copolymerizations procedure

Figure 5. VCM/VAc emulsion copolymerization (a) conversion vs. time in a batch reactor for extreme cases (b) instantaneous copolymer compostion (c) start-up procedures in an unseeded CSTR.

The copolymer composition may drift during the course of an emulsion copolymerization because of differences in monomer reactivity ratios or water solubilities. Various techniques have been developed to produce a uniform copolymer composition. The feed composition may be continuously or periodically enriched in a particular monomer, to compensate for its lower reactivity. A much more common procedure involves pumping the monomers into the reactor at such a rate that the extent of conversion is always very high [>about 90%]. This way, the polymer composition is always that of the last increment of the monomer feed. 

Abad C, de la Cal JC, Asua JM (1995) Start-up procedures in the emulsion copolymerization of vinyl esters in a continuous loop reactor. Polymer 36 4293-4299... 

Other Functional-group Latices.—There is considerable overlap here with the use of emulsion polymerization for the preparation of model colloids. Ahmed et al. have described the preparation of monodisperse sulphonated and sulphated polystyrene latices by surfactant-free emulsion copolymerization. The functional group monomers were sodium styrenesulphonate, sodium vinyltoluenesulphonate, sodium sulphoethyl methacrylate, and a commercial acrylic sulphate. Chonde and Krieger have described a procedure for the detection and removal of water-soluble oligomers in styrene-sodium styrenesulphonate copolymer latices produced by surfactant-free emulsion copolymerization. The essential step of the... 

After indicating the reasons for current industrial interest in carhoxylated latices, a general review is given of the production of these latices by emulsion copolymerization of the main monomers with minor amounts of unsaturated carboxylic acids. In addition to discussing the types of carboxylating acid which can be used, consideration is also given to surfactants, initiators, modifiers, electrolytes and post-polymerization treatments. The factors which affect the distribution of carboxylic-acid groups in the final latex are discussed these include the hydrophilicity of the carboxylic-acid monomer, the pH of the reaction system, and procedural aspects such as the way in which the acid monomer is added to the reaction system. The effects of carboxylic-acid monomers upon the rate of polymerization and the mechanism of particle nucleation are also reviewed. 

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. 

Starved-feed emulsion polymerization can be conducted without emulsifiers if suitable comonomers and procedures are utilized.341 Polymerization of a water-soluble methacrylate like HEMA in the presence of a CCT agent is carried out initially. The resulting HEMA oligomer is further copolymerized with hydrophobic monomers so that the resulting diblock copolymer serves as a surfactant (see, for instance, sections 5.3 and 5.4). During the cross-linking process, all of this surfactant is incorporated into the polymer backbone and is thus immobilized, overcoming the problem of residual surfactant in the final product. 

For practical purposes, styrene—DVB copolymers have commonly been obtained by the suspension polymerization method,[53, 54] which is well known to consist of heating and agitating a solution of initiator in monomers with an excess of water containing a stabilizer of the oil-in-water emulsion. Polymerization proceeds in suspended monomer droplets and, in this way, a beaded copolymer is obtained. While looking very simple, this procedure can provide many complications that significantly change the properties of the beaded product as compared to the properties of materials prepared by bulk copolymerization. AU parameters of the suspension copolymerization have to be strictly controlled, since even small deviations from optimal conditions of the synthesis can serve as an additional source of heterogeneity in the copolymer beads. [55]... 

Another strategy consists in the use of QDs coated with a cysteine acrylamide, a polymerizable stabilizer [304]. Successful incorporation of hydrophilic cysteine-acrylamide-stabilized QDs into 80-200 nm fluorescent latexes was achieved via emulsion polymerization, as reported by Sherman et al. [308], using two different procedures. In the first, a two-step shot growth surfactant-free emulsion polymerization of styrene and NaSS was performed in the presence of a solution of hydrophilic cysteine-acrylamide-stabilized CdS or CdSe/CdS QDs. In the second approach, CdSe/CdS QDs were first electrostatically modified by vinylbenzyl(trimethyl)-ammonium chloride and subsequently copolymerized with styrene in the presence of SDS. A third approach was also described in this paper coating of cationic PS particles with anionic poly(cysteine acrylamide)-coated QDs through electrostatic-driven interactions. 

Currently, commercially pure batch processes play a major role for suspension and bulk polymerization but only a minor role for emulsion polymerizations. The most important procedure for effecting polymer dispersions by emulsion polymerization on a technical scale is semibatch or feed processes, which are very flexible regarding product properties. Depending on the required properties with respect to particle size distribution, molecular weight distribution, chemical composition in the case of copolymerization, and particle morphology, numerous feeding policies have been developed. Almost all kinds of consecutive... 

Additionally to the procedures described earlier, improvements for thermostabilization is copolymerisation of vinyl chloride with suitable monomers. A great number of monomers were investigated to optimize the properties of resins. But only vinyl acetate, vinylidene chloride, ethylene, propylene, acrylonitrile, acrylic acid esters, and maleic acid esters, respectively, are of interest commercially [305,436,437]. The copolymerization was carried out in emulsion, suspension, and solution in connection with water- or oil-soluble initiators, as mentioned elsewhere. Another possibility for modifying PVC is grafting of VC on suitable polymers [305,438], blends of PVC with butadiene/styrene and butadiene/ methacryl acid esters copolymers [433], and polymer-analogous reactions on the macromolecule [439,440] (e.g., chlorination of PVC). 

The expansion of dispersed media ATRP to microemulsion provided the critical step required for development of a process for addition of pure monomer to the system to increase the percent solids in the final latex. This procedure was initially employed to prepare a forced gradient copolymer in a heterogeneous controlled copolymerization since the added pure monomer could diffuse to the latex partides containing all components required for an ATRP. An extension of the concept resulted in the development of an ab initio emulsion polymerization process, capable of directly preparing a stable latex containing block copolymers. The critical requirement for this advance in dispersed media ATRP was the ability to encapsulate all agents required for an ATRP in the initially formed micelles. This allowed pure monomer to be added to the reaction medium. The added monomer was then able to diffuse to the active micelles, allowing an increase in micelle size and concomitant increase in the percent solids and decrease in percent surfactants in the system. 

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