Emulsion copolymerization reaction

The water solubilities of the functional comonomers are reasonably high since they are usually polar compounds. Therefore, the initiation in the water phase may be too rapid when the initiator or the comonomer concentration is high. In such a case, the particle growth stage cannot be suppressed by the diffusion capture mechanism and the solution or dispersion polymerization of the functional comonomer within water phase may accompany the emulsion copolymerization reaction. This leads to the formation of polymeric products in the form of particle, aggregate, or soluble polymer with different compositions and molecular weights. The yield for the incorporation of functional comonomer into the uniform polymeric particles may be low since some of the functional comonomer may polymerize by an undesired mechanism. 

O. Elizalde, J.M. Asua and J.R. Leiza, Monitoring of high solids content starved-semi-batch emulsion copolymerization reactions by Fourier transform Raman spectroscopy, Appl. Spectrosc., 59, 1270-1279 (2005). 

Pinto, J.C. Dynamic optimization of semicontinu-ous emulsion copolymerization reactions composition and molecular weight distribution. Compos. Chem. Eng. 2001, 25 (4-6), 839-849. 

Figure 11 Overall MA mole fraction as a function of conversion for MA-VAc solution (°) and emulsion copolymerization reactions with MW ratios of ( ) 0.02 and (A) 0.3. Reprinted from Noel, L. F. J. van AItveer, J. L. Timmermans, M. D. F. German, A. L. J. Polym. Scl., Part A Polym. Chem. 1996, 34,1763-1770. ...

M. M. Reis, P. H. H. Araujo, C. Sayer, R. Giudici, Comparing near infrared and Raman spectroscopy for on-line monitoring of emulsion copolymerization reactions . Macro-molecular Symposia, 2004, 206, 135. 

Araujo PHH, de la Cal JC, Asua JM, Pinto JC. Modeling particle size distribution (PSD) in emulsion copolymerization reactions in a continuous loop reactor. In Piemcci S, editor. ESCAPE-10. Amsterdam Elsevier Science B.V. 2000. p 565-570. 

Continuous polymerization systems offer the possibiUty of several advantages including better heat transfer and cooling capacity, reduction in downtime, more uniform products, and less raw material handling (59,60). In some continuous emulsion homopolymerization processes, materials are added continuously to a first ketde and partially polymerized, then passed into a second reactor where, with additional initiator, the reaction is concluded. Continuous emulsion copolymerizations of vinyl acetate with ethylene have been described (61—64). Recirculating loop reactors which have high heat-transfer rates have found use for the manufacture of latexes for paint appHcations (59). 

Using copolymerization theory and well known phase equilibrium laws a mathematical model is reported for predicting conversions in an emulsion polymerization reactor. The model is demonstrated to accurately predict conversions from the head space vapor compositions during copolymerization reactions for two commercial products. However, it appears that for products with compositions lower than the azeotropic compositions the model becomes semi-empirical. 

Two different emulsion polymerization reactions were Investigated. One was the polymerization of acrylonitrile and methylacrylate (75/25 AN/MA) In the presence of an acrylonitrile elastomer (70/30 BD/AN) to produce a graft resin, llie second was the copolymerization oiE acrylonitrile and styrene (70/30 AN/S). Chromatographic analyses of latex solutions were conducted periodically during both types of polymerization reactions, using acetonitrile as latex solvent and chromatographic mobile phase. 

Fig. 56. Dependence of Mwof the microgels on the polymer yield in the anionic polymerization of EDMA in toluene by n-BuLi [254] (see Figure 53 caption for the reaction conditions). Reduced viscosity vs concentration of microgels a) Composition (mol %) N,N -methyl-enebisacrylamide (55%), methacrylamide (33%), methacrylic acid (2%), methacrylamido acetaldehyd-dimethylacetal (10%),measured at 20 °C in water, b) Composition (mol %) 1,4-DVB (35%), propenic acid amide-2-methyl-N-(4-methyl-2-butyl-l,3-dioxolane prepared by emulsion copolymerization and measured in dimethylformamide.

The reaction described in this example is carried out in miniemulsion.Miniemulsions are dispersions of critically stabilized oil droplets with a size between 50 and 500 nm prepared by shearing a system containing oil, water,a surfactant and a hydrophobe. In contrast to the classical emulsion polymerization (see 5ect. 2.2.4.2), here the polymerization starts and proceeds directly within the preformed micellar "nanoreactors" (= monomer droplets).This means that the droplets have to become the primary locus of the nucleation of the polymer reaction. With the concept of "nanoreactors" one can take advantage of a potential thermodynamic control for the design of nanoparticles. Polymerizations in such miniemulsions, when carefully prepared, result in latex particles which have about the same size as the initial droplets.The polymerization of miniemulsions extends the possibilities of the widely applied emulsion polymerization and provides advantages with respect to copolymerization reactions of monomers with different polarity, incorporation of hydrophobic materials, or with respect to the stability of the formed latexes. 

The emulsion copolymerization of BA with PEO-MA (Mw=2000) macromonomer was reported to be faster than the copolymerization of BA and MMA, proceeding under the same reaction conditions at 40 °C [100]. Polymerizations were initiated by a redox pair consisting of 1-ascorbic acid and hydrogen peroxide in the presence of a nonionic surfactant (p-nonyl phenol ethoxylate with 20 moles ethylene oxide). In the macromonomer system, the constant-rate interval 2 [9,10] was long (20-70% conversion). On the other hand, the interval 2 did not appear in the BA/MMA copolymerization and the maximum rate was lower by ca. 8% conversion min 1 and it was located at low conversions. 

The copolymerization of monomers where one of the monomers acts as the hydrophobe was reported by Reimers and Schork [26]. MMA was copolymerized with p-methylstyrene, vinyl hexanoate, or vinyl 2-ethylhexanoate. The resulting copolymer composition tended to follow the predictions of the reactivity ratios, i.e., the reaction progresses as a bulk reaction. In contrast, copolymer compositions obtained from the (macro)emulsion copolymerizations tended to be more influenced by the relative water solubility of the comonomer and mass transfer. Wu and Schork used monomer combinations with large differences in reactivity ratios and water solubility vinyl acetate/butyl acrylate,... 

Nonlinear polymer formation in emulsion polymerization is a challenging topic. Reaction mechanisms that form long-chain branching in free-radical polymerizations include chain transfer to the polymer and terminal double bond polymerization. Polymerization reactions that involve multifunctional monomers such as vinyl/divinyl copolymerization reactions are discussed separately in Sect. 4.2.2. For simplicity, in this section we assume that both the radicals and the polymer molecules that formed are distributed homogeneously inside the polymer particle. 

Schuller [150] and Guillot [98] both observed that the copolymer compositions obtained from emulsion polymerization reactions did not agree with the Mayo Lewis equation, where the reactivity ratios were obtained from homogeneous polymerization experiments. They concluded that this is due to the fact that the copolymerization equation can be used only for the exact monomer concentrations at the site of polymerization. Therefore, Schuller defined new reactivity ratios, TI and T2, to account for the fact that the monomer concentrations in a latex particle are dependent on the monomer partition coefficients (fCj and K2) and the monomer-to-water ratio (xp) ... 

The occurrence of a homogeneous reaction system is also implicit i n the derivation of the copolymer composition equation. Some polymers, like poly(vinylidene chloride), are insoluble in their own monomer and are not highly swollen by monomer. In emulsion copolymerizations of such reactants the relative concentrations of the comonomers in the polymerizing particles will be influenced by the amounts that can be adsorbed on the surface or absorbed into the interior of these polymerization loci. 

Free-radicals generated in many oxidation-reduction (or redox) reactions can be used to initiate chain poymerization. An advantage of this type of initiation is that, depending on the redox system used, radical production can occur at high rates at moderate (0-50°C) and even lower temperatures. Redox systems are generally used in polymerizations only at relatively low temperatures, a significant commercial example being the production of styrene-butadiene rubber by emulsion copolymerization of butadiene and styrene at 5-10°C ( cold recipe ). 

Polymers with pendant cyclic carbonate functionality were synthesized via the free radical copolymerization of vinyl ethylene carbonate (4-ethenyl-l,3-dioxolane-2-one, VEC) with other imsaturated monomers. Both solution and emulsion free radical processes were used. In solution copolymerizations, it was found that VEC copolymerizes completely with vinyl ester monomers over a wide compositional range. Conversions of monomer to polymer are quantitative with complete incorporation of VEC into the copolymers. Cyclic carbonate functional latex polymers were prepared by the emulsion copolymerization of VEC with vinyl acetate and butyl acrylate. VEC incorporation was quantitative and did not affect the stability of the latex. When copolymerized with acrylic monomers, however, VEC is not completely incorporated into the copolymer. Sufficient levels can be incorporated to provide adequate cyclic carbonate functionality for subsequent reaction and crosslinking. The unincorporated VEC can be removed using a thin film evaporator. The Tg of VEC copolymers can be modeled over the compositional range studied using either linear or Fox models with extrapolated values of the Tg of VEC homopolymer. 

Guillot J. Computer Simulation of Emulsion Copolymerization Processes for Monomers of Different Water Solubility. In Reichter KH, editor. Polymer Reaction Engineering. Heidelberg Hunthig Wepf Verlag 1986. p 147. 

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