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Analysis of the molecular weight distributions (MWDs) of polymer produced by pulsed-laser polymerization (PLP) is an effective method for the determination of free-radical propagation rate coefficients (k p). The PLP technique has been successfully applied to many slowly propagating monomers, but k p determination by PLP for faster propagating systems such as the acrylates is more difficult. Experimental conditions for the polymerization must be selected so that laser pulses are the dominant chain-starting and chain-stopping events. Interference from excessive chain-transfer reactions, or from termination reactions which are either too fast or too slow, results in MWDs which are not suitable for k p determination. Guidelines for design of successful experiments are outlined using an extensive n-butyl acrylate data set, from which k p has been determined over the temperature range 5−30 °C; limited data for n-dodecyl acrylate and 2-ethylhexyl acrylate are also presented.

Propagation rate coefficients, k p , for free-radical polymerization of butyl acrylate (BA) previously reported by several groups are critically evaluated. All data were determined by the combination of pulsed-laser polymerization (PLP) and subsequent polymer analysis by size exclusion (SEC) chromatography. The PLP-SEC technique has been recommended as the method of choice for the determination of k p by the IUPAC Working Party on Modeling of Polymerization Kinetics and Processes. Application of the technique to acrylates has proven to be very difficult and, along with other experimental evidence, has led to the conclusion that acrylate chain-growth kinetics are complicated by intramolecular transfer (backbiting) events to form a mid-chain radical structure of lower reactivity. These mechanisms have a significant effect on acrylate polymerization rate even at low temperatures, and have limited the PLP-SEC determination of k p of chain-end radicals to low temperatures (<20 8C) using high pulse repetition rates. Nonetheless, the values for BA from six different laboratories, determined at ambient pressure in the temperature range of À65 to 20 8C mostly for bulk monomer with few data in solution, fulfill consistency criteria and show excellent agreement, and are therefore combined together into a benchmark data set. The data are fitted well by an Arrhenius relation resulting in a preexponential factor of 2.21 Â 10 7 L Á mol À1 Á s À1 and an activation energy of 17.9 kJ Á mol À1 . It must be emphasized that these PLP-determined k p values are for monomer addition to a chain-end radical and that, even at low temperatures, it is necessary to consider the presence of two radical structures that have very different reactivity. Studies for other alkyl acrylates do not provide sufficient results to construct benchmark data sets, but indicate that the family behavior previously documented for alkyl methacrylates also holds true within the alkyl acrylate family of monomers.Arrhenius plot of propagation rate coefficients, k p , for BA as measured by PLP-SEC.

(1997). Critically evaluated rate coefficients for free-radical polymerization, 2. Propagation rate coefficients for methyl methacrylate. Macromolecular Chemistry and Physics, 198(5), 1545-1560. DOI: 10.1002/macp.1997 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. SUMMARYPulsed-laser polymerization (PLP) in conjunction with molar mass distribution (MMD) measurement is the method of choice for determining the propagation rate coefficient kp in free-radical polymerizations. The authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization, collate results from using PLP-MMD to determine kp as a function of temperature T for bulk free-radical polymerization of methyl methacrylate at low conversions and ambient pressure. Despite coming from several different laboratories, the values of $ are in excellent agreement and obey consistency checks. These values are therefore recommended as constituting a benchmark data set, one that is best fitted by The 95% joint confidence interval for these Arrhenius parameters is also given. In so doing, we describe the most appropriate statistical methods for fitting k&") data and then obtaining a joint confidence interval for the fitted Arrhenius parameters. As well, we outline factors which impose slight limitations on the accuracy of the PLP-MMD technique for determining $, factors which may apply even when this technique is functioning well. At the same time we discuss how such systematic errors in kp can be minimized.