Model vinyl polymerization kinetics

Detailed studies on the lipase-catalyzed polymerization of divinyl adipate and 1,4-butanediol were performed [41-44]. Bulk polymerization increased the reaction rate and molecular weight of the polymer however, the hydrolysis of the terminal vinyl ester significantly limited the formation of the polyester with high molecular weight. A mathematical model describing the kinetics of this polymerization was proposed, which effectively predicts the composition (terminal structure) of the polyester. 

In the case of polyester synthesis from divinyl esters, hydrolysis of the vinyl end group partly took place, resulting in the limitation of the polymer growth.201 A mathematical model showing the kinetics of the polymerization predicts the product composition. On the basis of these data, a batch-stirred reactor was designed to minimize temperature and mass-transfer effects.202 The efficient enzymatic production of polyesters was achieved using this reactor poly(l,4-butylene adipate) with Mn 2 x 104 was synthesized in 1 h at 60 °C. 

While the energy transfer model is remtarkably successful in summarizing the polymerization kinetics of vinyl monomer solutions, there may be other explanations w ith certain monomer-... 

Ciullo PA, Hewitt N (1999) The rubber formulary. Noyes, Norwich Coker K (2001) Modeling of chemical kinetics and reactor design. Gulf, Boston, MA Davis FJ (2004) Polymer chemistry a practical approach. Oxford University Press, Oxford Drobny JG (2001) Technology of fluoropolymers. CRC Press, Boca Raton, FL Durairaj RB (2005) Resorcinol chemistry technology and applications. Springer, Berlin Dutcher JR et al (eds) (2005) Soft materials structure and dynamics. Marcel Dekker, New York Erbil HY (2000) Vinyl acetate emulsion polymerization and copolymeiization with acrylic monomers. CRC Press, Boca Raton, FL... 

The kinetics of AN polymerization in solution follows that of the conventional models for ordinary vinyl polymerization as long as the monomer concentration is not too high. It has been shown that at concentrations above 4 M in DMF and 6 M in ethylene carbonate, the monomer acts as a nonsolvent and the mixture becomes heterogeneous. Polymerization rate and molecular mass proceed through a maximum in ethylene carbonate when the AN concentration is raised [648]. 

Chemistry and Kinetic Model of Radical Vinyl Polymerization... 

The synthesis and phase behavior of the model polydiethylsiloxane networks have also been studied. The networks were made by hydrosilylation of well-defined vinyl and allyl telechelic siloxanes obtained by kinetically controlled polymerization of cyclic trisiloxane.314 The effects of molecular weight between the cross-linkings on segment orientation in polydiethylsiloxane elastomers were studied.315... 

Model and Nature of Termination Step for Bulk Polymerization of Vinyl Acetate The following is a reasonable kinetic model for the bulk polymerization of vinyl acetate. 

The results definitely prove our hypotheses in the kinetic model for vinyl acetate emulsion polymerization (10), that vinyl radical, CH2=C-0Ac, is the major monomer radical formed and is a stable radical which reinitiates relatively slowly compared to the propagation step. 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

Chung, S.T., )ung, S.H., Kinetic modeling of commercial scale mass polymerization of vinyl chloride,... 

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... 

In general, a polymerization process model consists of material balances (component rate equations), energy balances, and additional set of equations to calculate polymer properties (e.g., molecular weight moment equations). The kinetic equations for a typical linear addition polymerization process include initiation or catalytic site activation, chain propagation, chain termination, and chain transfer reactions. The typical reactions that occur in a homogeneous free radical polymerization of vinyl monomers and coordination polymerization of olefins are illustrated in Table 2. 

Kinetic models determine the state of cure by predicting the concentration of reacting species from the solution of differential equations for each reacting species. Mikos et al. (1986) and Tobita and Hamielec (1989) have developed kinetic models for vinyl and free-radical network systems. Chain-growth polymerization has also been modelled through kinetic simulations by Okay (1994). 

Characteristic kinetic and morphological features of vinyl chloride radical polymerization processes were reviewed in89. While developing a mathematical model for the polymerization of this monomer, Canadian90 and Soviet91 investigators concentrated their attention on the heterophase nature of the process. In both cases the dependence of kinetic constants on the viscosity of the medium was disregarded. 

Case Study 2 Comparison of Mathematical Models FOR Free Radical Homopolymerization of Vinyl Monomers in scCOj In this case study, a comparison of performance of the different kinetic models proposed in the literature for dispersion polymerization of styrene and MMA in SCCO2 is presented. The models used by Quintero-Ortega et al. [43] (models 1 and 2) and those presented by the groups of Kiparissides [47] (model 3) and Morbidelli... 

Prior to Harwood s work, the existence of a Bootstrap effect in copolymerization was considered but rejected after the failure of efforts to correlate polymer-solvent interaction parameters with observed solvent effects. Kamachi, for instance, estimated the interaction between polymer and solvent by calculating the difference between their solubility parameters. He found that while there was some correlation between polymer-solvent interaction parameters and observed solvent effects for methyl methacrylate, for vinyl acetate there was none. However, it should be noted that evidence for radical-solvent complexes in vinyl acetate systems is fairly strong (see Section 3), so a rejection of a generalized Bootstrap model on the basis of evidence from vinyl acetate polymerization is perhaps unwise. Kratochvil et al." investigated the possible influence of preferential solvation in copolymerizations and concluded that, for systems with weak non-specific interactions, such as STY-MMA, the effect of preferential solvation on kinetics was probably comparable to the experimental error in determining the rate of polymerization ( 5%). Later, Maxwell et al." also concluded that the origin of the Bootstrap effect was not likely to be bulk monomer-polymer thermodynamics since, for a variety of monomers, Flory-Huggins theory predicts that the monomer ratios in the monomer-polymer phase would be equal to that in the bulk phase. 

---