Pulsed-Laser Polymerization/Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry:  An Approach toward Free-Radical Propagation Rate Coefficients of Ultimate Accuracy?

Free-radical polymerizations of styrene (S) and methyl methacrylate (MMA) in bulk were induced at 25 and 60 °C using a pulsed ultraviolet excimer laser. Molecular weight distributions (MWDs) of the polymer products produced were measured by both size exclusion chromatography and matrix-assisted laser desorption/ionization mass spectrometry and compared with one another. Propagation rate coefficients k p were determined from these MWDs taking into account impacts of varying termination rates and varying pulse periods as well as errors resulting from instrumental broadening. Values of k p(25 °C, S) = 96.5 L mol-1 s-1, k p(60 °C, S) = 364 L mol-1 s-1, k p(25 °C, MMA) = 372 L mol-1 s-1, and k p(60 °C, MMA) = 962 L mol-1 s-1 are finally suggested.