(621d) Kinetic Monte Carlo Simulation of Branch-Length Distribution in the Seeded, Semibatch Emulsion Polymerization of Butyl Acrylate

For monomers which readily undergo radical chain transfer to polymer, such as vinyl acetate and butyl acrylate, the final properties of a latex vary with the branching structure of the polymer. As shown by Plessis, et al., the level of branching and molecular weight distribution affect the adhesive properties of a poly(butyl acrylate-styrene) latex [1]. Former, et al. observed that the rheological properties of a poly(butyl acrylate) latex vary with the level of branching [2]. In butyl acrylate polymerizations, radicals are known to chain transfer via both intermolecular and intramolecular, or ?backbiting,? reactions [3]. In backbiting, a radical transfers to another mer in its own molecule, usually a small number of mers from the radical. Arzamendi and Leiza performed population-balance kinetic Monte Carlo simulations of a seeded, semibatch emulsion polymerization of butyl acrylate, and made the assumption that all backbiting reactions result in short-chain branches, while all intermolecular chain transfer reactions result in long-chain branches [4]. Short-chain branches reduce viscosity by increasing the spacing between molecules, while long chain branches increase viscosity by increasing the number of entanglements [2]. We have performed lattice KMC simulations of the backbiting reaction, incorporating diffusion, which give a distribution of the backbiting distance, and the resulting branch lengths. By incorporating this backbiting-distance distribution into a population-balance KMC simulation of the seeded, semibatch emulsion polymerization of butyl acrylate, we obtain a distribution of branch lengths, allowing us to more accurately predict the variation of particle viscosity with the level of branching.

[1] C. Plessis, G. Arzamendi, J. R. Leiza, H. A. S. Schoonbrood, D. Charmot, and J. M. Asua. Kinetics and polymer microstructure of the seeded semibatch emulsion copolymerization of n-butyl acrylate and styrene. Macromolecules, 34(15):5147?5157, 2001.

[2] C. Former, J. Castro, C. M. Fellows, R. I. Tanner, and R. G. Gilbert. Effect of branching and molecular weight on the viscoelastic properties of poly(butyl acrylate). Journal of Polymer Science Part A-Polymer Chemistry, 40(20):3335?3349, 2002.

[3] C. Plessis, G. Arzamendi, J. R. Leiza, H. A. S. Schoonbrood, D. Charmot, and J. M. Asua. Modeling of seeded semibatch emulsion polymerization of n-BA. Industrial & Engineering Chemistry Research, 40(18): 3883?3894, 2001.

[4] G. Arzamendi and J. R. Leiza. Molecular weight distribution (soluble and insoluble fraction) in emulsion polymerization of acrylate monomers by Monte Carlo simulations. Industrial & Engineering Chemistry Research, 47(16): 5934?5947, 2008.