A Simplified Predictive Tool for Design and Analysis of SET-LRP Reactions with Mechanistic Insight

Abstract

Single-electron transfer (SET)-living radical polymerization (LRP) is a robust, fast, “green,” grafting method, similar but different from atom transfer radical polymerization, that operates at ambient temperature in the presence of oxygen and is industrially attractive. Solving a simplified reaction model with only five rather than 12 reactions in solution, for describing the SET-LRP scheme and verifying it with experimental data, we provide (i) a useful tool to predict conversion given initial conditions and rate constants, and (ii) key mechanistic insights with a parametric sensitivity analysis, illustrating the effects of initial conditions, kinetic rate constants, temperature, and copper particle size. Findings include: (i) Increasing the formation rate of radicals (i.e., kact) exhibited a maximum in monomer conversion. (ii) The optimal ratio of initial conditions was found to be [MA]0/[PnX]0/[CuIIX2/L]0 = 222/1/1.5, where [MA]0 = 7.4 M. (iii) Increasing the temperature strongly improved monomer conversion with an inflection point. (iv) Using an order-of-magnitude and Damköhler number analysis, we provide a rationale for selecting small diameter particles and specify how they are likely to perform with SET-LRP reactions. Assumptions of the model include: Solid copper concentration was an infinite source of dissolved CuI and CuII and was available instantaneously (with Damköhler number ≪ 1, for reaction rather than diffusion limitation). Also, the reverse reaction of the disproportionation of CuI was negligible, polymer chain length did not affect reaction kinetics, and all intermediate reactions were neglected.