Acrylic polymerization model description

Acrylic polymerization model capability, 172,173f description, 172... 

The above example gives us an idea of the difficulties in stating a rigorous kinetic model for the free-radical polymerization of formulations containing polyfunctional monomers. An example of efforts to introduce a mechanistic analysis for this kind of reaction, is the case of (meth)acrylate polymerizations, where Bowman and Peppas (1991) coupled free-volume derived expressions for diffusion-controlled kp and kt values to expressions describing the time-dependent evolution of the free volume. Further work expanded this initial analysis to take into account different possible elemental steps of the kinetic scheme (Anseth and Bowman, 1992/93 Kurdikar and Peppas, 1994 Scott and Peppas, 1999). The analysis of these mechanistic models is beyond our scope. Instead, one example of models that capture the main concepts of a rigorous description, but include phenomenological equations to account for the variation of specific rate constants with conversion, will be discussed. 

To represent dispersion polymerization in conventional liquid media, several models have been reported in the literature, mainly focused on the particle formation and growth [33, 34] or on the reaction kinetics. Since our first aim is the reliable description of the reaction kinetics, we focus on the second type of models only. The model developed by Ahmed and Poehlein [35, 36], applied to the dispersion polymerization of styrene in ethanol, was probably the first one from which the polymerization rates in the two reaction loci have been calculated. A more comprehensive model was later reported by Saenz and Asua [37] for the dispersion copolymerization of styrene and butyl acrylate in ethanol-water medium. The particle growth as well as the entire MWD were predicted, once more evaluating the reaction rates in both phases and accounting for an irreversible radical mass transport from the continuous to the dispersed phase. Finally, a further model predicting conversion, particle number, and particle size distribution was proposed by Araujo and Pinto [38] for the dispersion polymerization of styrene in ethanol. 

In conclusion it can be said that the MWD method is capable of determining the chain-length dependence of kt model-independently. This method has been validated theoretically and, as long as the number MWD can be determined and scaled correctly, the method is robust and reliable. In this thesis, the first model-independent results have been reported for a set of three acrylates. These results will enable a better description of the overall kinetics of free-radical polymerizations and better predictions of the resulting MWDs and polymer properties. It is sincerely hoped that this method and lines of thought presented will find continuation in future scientific work by others in this field of great scientific interest and practical importance. 

Until now the viscosity function has just been measured without a relationship to the kinetic of the reaction. The model of Malkin and KuUchiklim was introduced and their advantages and problems were discussed earlier. Nevertheless, a complete description of the rheokinetics is not the focus of this investigation. But a more detailed understanding in the relationship of viscosity and the polymerization is found, when stopping the progress of polymerization in the rheometer. In Fig. 20.18 results from stop test at certain stop times are shown. With the determination of the conversion at different stop times at different concentrations of acrylic acid, the... 

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