Scope for Accessing the Chain Length Dependence of the Termination Rate Coefficient for Disparate Length Radicals in Acrylate Free Radical Polymerization

Abstract

Summary: A method that utilizes reversible addition fragmentation chain transfer (RAFT) chemistry is evaluated on a theoretical basis to deduce the termination rate coefficient for disparate length radicals k s;l t in acrylate free radical polymerization, where s and l represent the arbitrary yet disparate chain lengths from either a ''short'' or ''long'' RAFT distribution. The method is based on a previously developed method for elucidation of k s;l t for the model monomer system styrene. The method was expanded to account for intramolecular chain transfer (i.e., the formation of mid-chain radicals via backbiting) and the free radical polymerization kinetic parameters of methyl acrylate. Simulations show that the method's predictive capability is sensitive to the polymerization rate's dependence on monomer concentration, i.e., the virtual monomer reaction order, which varies with the termination rate coefficient's value and chain length dependence. However, attaining the virtual monomer reaction order is a facile process and once known the method developed here that accounts for mid-chain radicals and virtual monomer reaction orders other than one seems robust enough to elucidate the chain length dependence of k s;l t for the more complex acrylate free radical polymerization.

The Effect of Intramolecular Transfer to Polymer on Stationary Free‐Radical Polymerization of Alkyl Acrylates, 3 – Consideration of Solution Polymerization up to High Conversions

“…This conclusion is based on numerous experimental [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical [18][19][20][21][22][23][24] investigations. According to these investigations, the mechanism of the intermolecular chain transfer reaction is a 1,5-hydrogen shift that occurs through a six-membered ring structure.…”

The RAFT Process as a Kinetic Tool: Accessing Fundamental Parameters of Free Radical Polymerization

“…ω is equal to 1.2, 1.5 and 2.5 when α in and ϕ in are equal to 0.16, 0.4 and 0.8, respectively [96]. Additionally, when backbiting and virtual monomer reaction orders greater than 1 are accounted for, the method predicts ϕ out better than the method that considers only fast propagation (see Figs.…”

“…Solving equation 4.6 for k t provides the termination rate coefficient averaged as a function of time (equation 4.7; note that t 0 R P (t) dt = c M ), when the initiator decomposition rate coefficient, the propagation rate coefficient as well as the initiator efficiency are available [92,96].…”

“…Modeling is a useful tool for developing new techniques, and thus was used to demonstrate that reliable information about k i, j t can be obtained from direct measurement of the polymerization rate [35,96]. To the best of our knowledge, this method and analytical approach is the first thorough analysis of a method and procedure that quantifies k s ,l t .…”

Design Criteria for Accurate Measurement of Bimolecular Radical Termination Rate Coefficients via the RAFT‐CLD‐T Method

“…[11,17,18] Alternatively, the RAFT-CLD-T method, in conjunction with knowledge about k i;i t (x), may itself be employed to extract k i;j t (x) experimentally, as detailed in a recent study. [19] Importantly, quantification of k i;j t (where i and j can vary over a wide range of chain lengths) at each conversion allows the calculation of the overall average rate coefficient for termination, hk t i, for a broad distribution of chain lengths [see Equation (2)]. Access to average termination rate coefficients under any polymerization scenario -including those found in conventional free-radical polymerizations [20] -is essential for accurate kinetic modeling of polymerization rates and molecular weight distribution evolution with conversion.…”