Emulsion copolymerization model

To our knowledge, this is the first time that an emulsion copolymerization model has been developed based on a population balance approach. The resulting differential equations are more involved and complex than those of the homopolymer case. Lack of experimental literature data for the specific system VCM/VAc made it impossible to directly check the model s predictive powers, however, successful simulation of extreme cases and reasonable trends obtained in the model s predictions are convincing enough about the validity and usefulness of the mathematical model per se. 

Recently, ESR techniques have been applied to study polymerization reactions in heterogeneous phase, for example, emulsion polymerization. The development of the direct measurements of radical concentration by ESR represents a major advance in obtaining reliable data on important parameters in emulsion copolymerization modeling, snch as propagation rate coefficients or termination rate coefficients as functions of chain length and conversion [140,141],... 

Unzueta et al. [18] derived a kinetic model for the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) employing both the micellar and homogeneous nucleation mechanisms and introducing the radical absorption efficiency factor for micelles, F, and that for particles, Fp. They compared experimental results with model predictions, where they employed the values of Fp=10 and Fn,=10", respectively, as adjustable parameters. However, they did not explain the reason why the value of Fp, is an order of magnitude smaller than the value of Fp. Sayer et al. [19] proposed a kinetic model for continuous vinyl acetate (VAc) emulsion polymerization in a pulsed... 

Ldpez et al. [55] investigated the kinetics of the seeded emulsion copolymerization of St and BA in experiments where the diameter and number of seed particles, and the concentration of initiator were widely varied. The experimental data were fitted with a mathematical model in which they used the desorption rate coefficient developed by Forcada et al. [56] for a copolymerization system. The desorption rate coefficient for the A-monomeric radical that they used was a modification of Eq. 22 and Eq. 23, and is given by... 

By combining thermodynamically-based monomer partitioning relationships for saturation [170] and partial swelling [172] with mass balance equations, Noel et al. [174] proposed a model for saturation and a model for partial swelling that could predict the mole fraction of a specific monomer i in the polymer particles. They showed that the batch emulsion copolymerization behavior predicted by the models presented in this article agreed adequately with experimental results for MA-VAc and MA-Inden (Ind) systems. Karlsson et al. [176] studied the monomer swelling kinetics at 80 °C in Interval III of the seeded emulsion polymerization of isoprene with carboxylated PSt latex particles as the seeds. The authors measured the variation of the isoprene sorption rate into the seed polymer particles with the volume fraction of polymer in the latex particles, and discussed the sorption process of isoprene into the seed polymer particles in Interval III in detail from a thermodynamic point of view. 

Saldivar, E. Dafniotis, P. Ray, W.H. Mathematical modeling of emulsion copolymerization reactors. I. Model formulation and application to reactors operating with micellar nucleation. J. Macromol. Sci. Rev. Macromol. Chem. Phys. 1998, C38 (2), 207-325. 

Saldivar, E. Araujo, O. Giudici, R. Guerrero-Sanchez, C. Modeling and experimental studies of emulsion copolymerization systems. Ill acrylics. J. Appl. Polym. Sci. 2002, 84, 1320-1338. 

We are currently exploring new routes to the synthesis of ionomers with controlled architecture, i.e. with control over the amount and location of ionic groups in the polymer backbone. One of our main interests is the synthesis of ion containing block copolymers. The applicability of anionic polymerization in the synthesis of block copolymers and other well defined model systems is well documented (22-24) Not as well appreciated, however, is the blocky nature that certain emulsion copolymerizations may provide. Thus, we have utilized both anionic and free radical emulsion polymerization in the preparation of model ionomers of controlled architecture. In this paper, the synthesis and characteristics of sulfonated and carboxylated block ionomers by both free radical emulsion and anionic polymerization followed by hydrolysis will be discussed. 

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. 

Dafniotis P, Saldivar E. Modeling emulsion copolymerization reactors. Kinetics and monomer partition [Term Project Che 730 Chemical Reactor Principles. Madison Department of Chemical Engineering, University of Wisconsin May 1990. 

EGDMA is also a clear liquid which is insoluble in water, and has a boiling point of 260 °C (at 1 atm) [50]. As an example of the application of EGDMA in emulsion polymerization systems, Tobita et al. recently modelled the kinetics of homogeneous crosslinking during the emulsion copolymerization of EGDMA with methyl methacrylate, and described the evolution of crosslink density with time (i.e., conversion) [51]. 

In the previous section, copolymer eomposition drift was discussed without considering the effects of differences in the water solubility of the monomers. This can lead to soious aims in the modelling of emulsion copolymerization and failure to account for partitioning is a source of uncert ty in many of the values of reactivity ratios de mined from pulsion polymmzation data. 

Another general approach is to use so-called optimum monomer addition rate profiles, which involves addition of monomers at rates wluch vary with time in a manner calculated to maintain the comonomer composition constant. This approach requires a quantitative model for the particular emulsion copolymerization which is to be controlled and hence requires thorough knowledge of partitioning, reactivity ratios, rate coefficients, etc. Two strategies have been employed [28, 75-80] ... 

In copolymerization, control of the copolym composiricm can be obtained when applying monomer addition profiles. These monomer addition profiles either can be based on the direct translation of on-line measurements to monomer addition steps (controlled ccxnposiritxi reactor) or the profiles can be predicted by emulsion copolymoization models on a conversion basis. The required conversion-time relation is then obtained by on-line measurements. 

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