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 chromatog. (SEC) combined with pulsed laser polymn. has been used to evaluate propagation rate coeffs. (kp) in bulk free-radical polymn. for the systems Me methacrylate and styrene. By varying laser frequencies, the relation between polymer chain length and obsd. propagation rate coeff. (kpobs) has been investigated in detail. It has been found that deviations between MALDI-ToF-MS and SEC at higher mol. wts. are the result of instrumental effects in SEC. Moreover, using a model and taking into account exptl. studies on the propagation of oligomeric species, it has been inferred that the relationship between kpobs 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 mol. wts