Methyl methacrylate emulsion polymerization

A decrease in ktp during polymerization will cause a and m to increas e. A decrease in m will tend to reduce n while an increase in a will cause an increase in ii. It follows from Figure 3 that the effect of a decrease in m on ii is only slightly smaller than the effect of a corresponding increase in a, i.e. the net-effect on ii is very small and therefore gel-effect has a much smaller influence on polymerization rate in vinyl acetate than in typical styrene and methyl methacrylate emulsion polymerization. However, since the desorption rate constant kvinyl acetate polymerization, ii will in fact increase and therefore the rate of polymerization will not be first order with respect to [Mp]. But, this is not due to gel-effect as defined in this paper. 

Systems Where Radical Desorption is Negligible. Styrene and methyl methacrylate emulsion polymerization are examples of systems where radical desorption can be neglected. In Figures 4 and 5 are shown comparisons between experimental and theoretical conversion histories in methyl methacrylate and styrene polymerization. The solid curves represent the model, and it appears that there is excellent agreement between theory and experiment. The values of the rate constants used for the theoretical simulations are reported in previous publications (, 3). The dashed curves represent the corresponding theoretical curves in the calculation of which gel-effect has been neglected, that is, ktp is kept constant at a value for low viscosity solutions. It appears that neglecting gel-effect in the simulation of styrene... 

Molecular Weight Development in Styrene and Methyl Methacrylate Emulsion Polymerization... 

P3 = poly(methyl methacrylate). Emulsion polymerization, no new particles (Example 7)... 

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

Methyl methacrylate is polymerized to poly(methyl methacrylate), which is used in cast and extruded sheet (32%), surface coatings (24%), molding powder and resins (15%), impact modifiers (13%), and emulsion polymers... 

Uses. The azobisnitriles have been used for bulk, solution, emulsion, and suspension polymerization of all of the common vinyl monomers, including ethylene, styrene vinyl chloride, vinyl acetate, acylonitrile, and methyl methacrylate. The polymerizations of unsaturated polyesters and copolymerizations of vinyl compounds also have been initiated by these compounds. 

By conventional emulsion polymerization procedures, a crosslinked copolymer of butyl acrylate and 1% allyl methacrylate was formed in the presence of methyl methacrylate. Then additional methyl methacrylate is polymerized in the system. The resultant product was a poly(methyl methacrylate) with improved... 

A technique has been developed for the continuous measurement of emulsion surface tension based on the pressure necessary to form a bubble in liquid. Details of the method may be found in Schork and Ray [24]. With a laboratory prototype of the bubble tensiometer, it has been possible to measure surface tensions continuously to within 1 to 2% [24]. A commercial instrument based on these principles is now available. Figures 5.5 and 5.7 demonstrate the use of the bubble tensiometer to monitor the surface tension of methyl methacrylate emulsion during continuous and batch polymerization. It will be noted that during conversion oscillation the surface tension oscillated as well, in accordance with the discrete initiation mechanism often postulated to explain this phenomenon. 

Besides two-component LIPNs, three-component LIPNs have also been studied through three-stage emulsion polymerization processes (Zhang et al. 1991, 1994 Isao et al. 1992). These authors synthesized poly(n-butyl acrylate) cross-linked with ethylene glycol dimethacrylate as the seed latex. Styrene and divinylbenzene were added at the second stage. The third stage was linear poly(methyl methacrylate). Starved polymerization conditions resulted in more regular-shaped latex particles than batch addition of monomer. 

Sajjadi [85] investigated the diffusion-controlled nucleation and growth of particle nuclei in the emulsion homopolymerizations of styrene and methyl methacrylate. The polymerization starts with two stratified layers of monomer and water containing surfactant and initiator, with the water layer being stirred gently. In this manner, the rate of transport of monomer becomes diffusion-limited. As a result, the rate of growth of particle nuclei is reduced significantly, and more latex particles can be nucleated in emulsion polymerization. 

Acrylics. Acetone is converted via the intermediate acetone cyanohydrin to the monomer methyl methacrylate (MMA) [80-62-6]. The MMA is polymerized to poly(methyl methacrylate) (PMMA) to make the familiar clear acryUc sheet. PMMA is also used in mol ding and extmsion powders. Hydrolysis of acetone cyanohydrin gives methacrylic acid (MAA), a monomer which goes direcdy into acryUc latexes, carboxylated styrene—butadiene polymers, or ethylene—MAA ionomers. As part of the methacrylic stmcture, acetone is found in the following major end use products acryUc sheet mol ding resins, impact modifiers and processing aids, acryUc film, ABS and polyester resin modifiers, surface coatings, acryUc lacquers, emulsion polymers, petroleum chemicals, and various copolymers (see METHACRYLIC ACID AND DERIVATIVES METHACRYLIC POLYMERS). 

Emulsion Polymerization. Emulsion polymerization is the most important industrial method for the preparation of acryhc polymers. The principal markets for aqueous dispersion polymers made by emulsion polymerization of acryhc esters are the paint, paper, adhesives, textile, floor pohsh, and leather industries, where they are used principally as coatings or binders. Copolymers of either ethyl acrylate or butyl acrylate with methyl methacrylate are most common. 

Recently, Smigol et al. [75] extensively studied emulsifier-free emulsion polymerization of different monomers including styrene, methyl methacrylate, and glycidyl methacrylate in an aqueous medium by using potassium peroxydisulfate as the initiator. In this study. 

In another study, uniform composite polymethyl-methacrylate/polystyrene (PMMA/PS) composite particles in the size range of 1-10 fim were prepared by the seeded emulsion polymerization of styrene [121]. The PMMA seed particles were initially prepared by the dispersion polymerization of MMA by using AIBN as the initiator. In this polymerization, poly(7V-vinyl pyrolli-done) and methyl tricaprylyl ammonium chloride were used as the stabilizer and the costabilizer, respectively, in the methanol medium. Seed particles were swollen with styrene monomer in a medium comprised of seed particles, styrene, water, poly(7V-vinyl pyrollidone), Polywet KX-3 and aeorosol MA emulsifiers, sodium bicarbonate, hydroquinone inhibitor, and azobis(2-methylbu-... 

This paper presents the physical mechanism and the structure of a comprehensive dynamic Emulsion Polymerization Model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles, the monomer conversions, the copolymer composition, and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations. 

The Emulsion Polymerization Model (EPM) described in this paper will be presented without a detailed discussion of the model equations due to space limitations. The complete set of equations has been presented in a formal publication (Richards, J. R. et al. J. AppI. Poly. Sci . in press). Model results will then be compared to experimental data for styrene and styrene-methyl methacrylate (MMA) copolymers published by various workers. 

The role of water in these reactions is not completely clear since the applied metal complexes are not water-soluble. One reason for using aqueous systems is the possibility of producing aqueous emulsion directly which is a distinct technological benefit. Nevertheless, in polymerizations of methyl methacrylate with [RuCl2(PPh3)3] and PhCOCHCl2, consistently higher reaction rates were observed in the presence of water than in diy toluene [48]. 

Emulsion polymerization is used for 10-15% of global polymer production, including such industrially important polymers as poly(acrylonitrile-butadiene-styrene) (ABS), polystyrene, poly(methyl methacrylate), and poly (vinyl acetate) [196]. These are made from aqueous solutions with high concentrations of suspended solids. The important components have unsaturated carbon-carbon double bonds. Raman spectroscopy is well-suited to address these challenges, though the heterogeneity of the mixture sometimes presents challenges. New sample interfaces, such as WAI and transmission mode, that have shown promise in pharmaceutical suspensions are anticipated to help here also. 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

Monomer and initiator must be soluble in the liquid and the solvent must have the desired chain-transfer characteristics, boiling point (above the temperature necessary to carry out the polymerization and low enough to allow for ready removal if the polymer is recovered by solvent evaporation). The presence of the solvent assists in heat removal and control (as it also does for suspension and emulsion polymerization systems). Polymer yield per reaction volume is lower than for bulk reactions. Also, solvent recovery and removal (from the polymer) is necessary. Many free radical and ionic polymerizations are carried out utilizing solution polymerization including water-soluble polymers prepared in aqueous solution (namely poly(acrylic acid), polyacrylamide, and poly(A-vinylpyrrolidinone). Polystyrene, poly(methyl methacrylate), poly(vinyl chloride), and polybutadiene are prepared from organic solution polymerizations. 

Case 3 behavior occurs when the particle size is sufficiently large (about 0.1-1 pm) relative to kt such that two or more radicals can coexist in a polymer particle without instantaneous termination. This effect is more pronounced as the particle size and percent conversion increase. At high conversion the particle size increases and k, decreases, leading to an increase in h. The increase in h occurs at lower conversions for the larger-sized particles. Thus for styrene polymerization it increases from 0.5 to only 0.6 at 90% conversion for 0.7-pm particles. On the other hand, for 1.4-pm particles, n increases to about 1 at 80% conversion and more than 2 at 90% conversion [Chatterjee et al., 1979 Gerrens, 1959]. Much higher values of h have been reported in other emulsion polymerizations [Ballard et al., 1986 Mallya and Plamthottam, 1989]. Methyl methacrylate has a more pronounced Trommsdorff effect than styrene and vinyl acetate, and this results in a more exaggerated tendency toward case 3 behavior for methyl methacrylate. 

The heat of an emulsion polymerization is the same as that for the corresponding bulk or solution polymerization, since AH is essentially the enthalpy change of the propagation step. Thus, the heats of emulsion polymerization for acrylic acid, methyl acrylate, and methyl methacrylate are —67, —77, and —58 kJ mol-1, respectively [McCurdy and Laidler, 1964], in excellent agreement with the AH values for the corresponding homogeneous polymerizations (Table 3-14). 

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