Application of Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry in Pulsed Laser Polymerization. Chain-Length-Dependent Propagation Rate Coefficients at High Molecular Weight:  An Artifact Caused by Band Broadening in Size Exclusion Chromatography?

The combination of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF-MS) and size exclusion chromatography (SEC) combined with pulsed laser polymerization has been used to evaluate propagation rate coefficients (kp) in bulk free-radical polymerization for the systems methyl methacrylate and styrene. By varying laser frequencies, the relation between polymer chain length and observed propagation rate coefficient ( ) has been investigated in detail. It has been found that deviations between MALDI-ToF-MS and SEC at higher molecular weights are the result of instrumental effects in SEC. Moreover, using a model and taking into account experimental studies on the propagation of oligomeric species, it has been inferred that the relationship between and polymer chain length is the result of chain-length-dependent behavior of the true kp in the oligomeric range, therewith excluding any chain-length-dependent behavior at higher molecular weights.