MALDI-TOF Detection of Olefin Structural Isomerization in Metathesis Chemistry

Abstract

MALDI-TOF mass spectrometry has been employed to examine polymers generated via acyclic diene metathesis (ADMET) polymerization using a ruthenium metathesis catalyst at 50 °C, a study which targets the analysis of ADMET polymers having amino acid pendant groups placed at specific positions along the polyolefin backbone. The MALDI spectra clearly delineate olefin isomerization chemistry which competes with propagation when catalyst 2 is employed, the result being loss of precise control of polymer structure. The distribution of peaks in the MALDI spectra matches the distribution pattern of gas chromatography (GC) peaks obtained for other ADMET polymers, leading to the following conclusions. First, structural isomerization and metathesis occur concurrently rather than in any kind of sequence. Second, the relative amount of isomerized chains produced dominates over the amount of nonisomerized products. In contrast to GC, MALDI analysis unequivocally identifies the mass of the oligomeric chains, allowing for increased confidence in assignment of the possible chain structures.