Kinetic Modeling of RAFT Polymerization via Dithiobenzoate Agents Considering the Missing Step Theory

- First report on modeling of the Missing Step Theory in RAFT via dithiobenzoates.
- The model is able to predict the behavior of the 2-arm and 3-arm intermediates.
- Solution of very large dimension population balance equation system.
- Comparison of the Methyl Acrylate and Styrene experimental data and the model results.
- The QSSA of 3-arm intermediate species is strictly validated.

The reversible addition-fragmentation chain transfer (RAFT) polymerization via dithiobenzoates with reactivation of the 2-arm intermediates in the kinetic mechanism, proposed by Buback and Vana in the Missing Step theory, was modeled for first time via the Reduced Stiffness by Quasi Steady State Approximation (RSQSSA) methodology. The methyl acrylate (MA) and the styrene (Sty) polymerization were analyzed by a comparison of the theoretical solution with the experimental data collected in the literature. The Quasi-Steady State was valid for the 3-arm intermediates only when the kinetic rate constant of reactivation of these species was close to or above the values of the addition rate coefficient. For both MA and Sty polymerizations, the simulations demonstrated a good agreement between the model solutions and experimental values, in the evolution of conversion with time, Mn and Mw. Also, the full-molecular weight distribution predicted by the model indicated a very good match with the experimental data. A symmetric bivariate population of 2-arm intermediates was obtained, resulting in a high probability to find species with the same chain length in both arms. Similarly, the results showed that the 3-arm intermediates with the same chain length in each arm could be mostly generated, but in this case a no-symmetric multivariate population was found.

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