Thermal self polymerization investigated by microwave molecular spectroscopy: Rotational characterization of the methyl methacrylate dimer

Rotational constants, Watson's S centrifugal distortion coefficients, and internal rotation parameters of the methyl methacrylate dimer were retrieved from the microwave spectrum of the dimer phase of methyl methacrylate, which was subjected to a thermal self-polymerization process. The dimer contains three methyl rotors. Coupling of the methyl internal rotation to the overall rotation causes a complicated splitting of the rotational spectrum. The fact that only the two methoxymethyl groups contributed resolvable (>5kHz) splittings simplified the spectral assignment somewhat and a fit of spectroscopic parameters to the experimental data was achieved to within experimental accuracy. The methyl methacrylate self-polymerization system is intended as an easily accessible model system for polymerization and the analysis of the dimer presented in this study contributes to the stepwise understanding by means of microwave spectroscopy and ab initio methods.