Solvent Effects in Butyl Acrylate and Vinyl Acetate Homopolymerizations in Toluene R. Jovanovic ´, M. A. Dube ´ Department of Chemical Engineering, University of Ottawa, Ottawa, 161 Louis Pasteur St., Ottawa, Ontario K1N 6N5, Canada Received 23 December 2003; accepted 16 March 2004 DOI 10.1002/app.20779 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A series of butyl acrylate (BA) and vinyl acetate (VAc) homopolymerizations in toluene was con- ducted to investigate the effect of solvent at different solvent and chain transfer agent (CTA) concentrations. Because the experimental determination of the individual propagation and termination rate constants for these systems is challeng- ing, experimental observations were limited to the lumped rate constant (k p /k t 0.5 ). Differences in the lumped rate con- stant, at different solvent and CTA concentrations, were assumed to be attributed to the effect of solvent on the termination rate constant. Our hypothesis was that the ter- mination rate constant k t was affected by the presence of solvent. At higher solvent concentrations, chain transfer to solvent occurs more frequently and leads to the formation of shorter chains, which move more easily and are able to terminate more quickly compared to longer chains. Thus, k t will increase, leading to a decrease in the lumped rate con- stant. The experimental results confirmed the presence of a solvent effect on the lumped rate constant. This effect was more pronounced in the case of VAc compared to BA solu- tion homopolymerizations. Under the investigated condi- tions, increased CTA concentrations did not substantially affect the rate of BA homopolymerizations, whereas a slight synergistic effect between the CTA and solvent at higher CTA and solvent concentrations was apparent for VAc ho- mopolymerizations. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 871– 876, 2004 Key words: radical polymerization; kinetics (polym.); mod- eling; solvent effect; lumped rate constant INTRODUCTION Although stricter environmental regulations and con- sumer awareness play a major role in the development of new environmentally friendly technologies for poly- mer production, solution polymerization remains an im- portant technology. It enables the production of poly- mers with superior properties compared to other tech- nologies, despite its shortcomings. Therefore, there is considerable interest on the effect of various solvents on the kinetics of free-radical polymerization of commer- cially important monomers such as methyl methacrylate (MMA), butyl acrylate (BA), vinyl acetate (VAc), and styrene (St). According to the classical free-radical poly- merization approach, the overall rate of polymerization (R p ) is represented using the following equation: R p = k p 2fk d k t  1/2  M I  1/2 where k p is the propagation rate constant; k t is the termination rate constant; k d is the initiator decompo- sition rate constant; f is initiator efficiency; and [M] and [I] are the monomer and initiator concentrations, respectively. In the presence of solvent, for some monomer–solvent systems, a strong dependency of R p on monomer concentration was observed. 1–7 One can speculate that all rate constants as well as initiator efficiency can be affected by the presence of the sol- vent. The effect of solvent on f and k d depends on the solvent–monomer system. Fernandez-Garcia et al. 1 found that for the BA– benzene system with AIBN initiator at 50°C, the 2fk d factor increased with mono- mer concentration up to [M]  3 mol/L, beyond which it became constant. Solvent effects on the propagation and termination rate constants have generated considerably more inter- est. Coote et al. 2 reviewed the main mechanisms by which solvent can affect the kinetics of solution polymer- ization such as by polarity effects, the formation of radi- cal–solvent complexes or monomer–solvent complexes, and the bootstrap effect. In almost all cases, the reactivity of the propagating radicals was assumed to be affected by the presence of the solvent. Neither of the proposed mechanisms is generally valid for all monomers. For example, the decrease in the polymerization rate with the increased initial concentration of aromatic solvents can be explained by the formation of monomer–solvent and radical–solvent complexes. Othman et al. 7 pointed out that the above-mentioned theories can explain the Correspondence to: M. Dube ´ (dube@genie.uottawa.ca). Contract grant sponsor: University of Ottawa. Contract grant sponsor: Natural Science and Engineering Research Council (NSERC) of Canada. Journal of Applied Polymer Science, Vol. 94, 871– 876 (2004) © 2004 Wiley Periodicals, Inc.