EPR Analysis of n‐Butyl Acrylate Radical Polymerization

Abstract

Via electron paramagnetic resonance (EPR) spectroscopy, concentrations of secondary propagating radicals (SPRs) and tertiary mid-chain radicals (MCRs) in n-butyl acrylate solution polymerization were measured. The EPR spectrum is dominated by the 4-line spectrum of SPRs at -50 °C and by the 7-line spectrum of MCRs at +70 °C. At intermediate temperatures, a third spectral component is seen, which is assigned to an MCR species with restricted rotational mobility. The MCR components are produced by 1,5-hydrogen shift (backbiting) of SPRs. The measured ratio of MCRs to SPRs allows for estimating the rate coefficient k pt for monomer addition to a mid-chain radical. For 70 °C, k pt is obtained to be 65.5 L · mol(-1) · s(-1) .

Chain‐Length‐Dependent Termination in Radical Polymerization of Acrylates

“…From EPR studies it may now be stated with certainty that at 60 and 80 °C, the fraction of MCRs in BA polymerization is around 80 %. [12] Thus it seems likely that the previously reported α s values for acrylates are artifacts from the presence of MCRs, meaning that the measured values of k t i,i contained significant contributions also from k t t,t and k t s,t . Indeed, when Barth et al…”

“…The first purpose of these spectra is to identify the radicals present. It can be seen in Figure 1 that the chain-end radicals (SPRs), which give rise to the 4 broad lines, [12] strongly dominate the spectrum at these low temperatures. The MCR line positions that are known from EPR spectra at higher temperatures [10,12] are also indicated in the figure.…”

“…It can be seen in Figure 1 that the chain-end radicals (SPRs), which give rise to the 4 broad lines, [12] strongly dominate the spectrum at these low temperatures. The MCR line positions that are known from EPR spectra at higher temperatures [10,12] are also indicated in the figure. The absence of any significant signal at any of these line positions evidences that the MCR contribution to termination rate must be negligible.…”

“…Most studies have concentrated on butyl acrylate (BA), [1][2][3][4][5][6][7][8][9][10][11][12][13] with this monomer being taken as typical of the entire family. Understanding of the polymerization kinetics of acrylate-type monomers is important not just for scientific reasons, but also because the industrial importance of these monomers makes it essential that their kinetic behavior can be well modeled.…”

On the Use of Quantum Chemistry for the Determination of Propagation, Copolymerization, and Secondary Reaction Kinetics in Free Radical Polymerization

“…Since its invention in the late 1980s, PLP-based techniques have substantially improved the quality of the experimental measurements of rate parameters in FRP, particularly for propagation reactions. These techniques have also been widely used for the study of the homopolymerization and copolymerization of various monomers [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”