June 1999
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Macromolecular Chemistry and Physics
The electron density distributions of the four possible configurational isomers of the monomer vinylformamide (VFA) and of the cationically propagating species were examined by means of quantum chemical calculations. They show that the electrophilic attack of the propagating chain at the carbonyl oxygen of the VFA monomer is kinetically controlled whereas the attack at the C=C bond of the VFA is thermodynamically controlled. For experimental proving of this theoretical argument, VFA is cationically polymerized in toluene at different reaction temperatures by means of iodine, trifluoromethanesulfonic acid (HOTf), and trimethylsiliyl triflate (TMST) as initiators. Head group functionality and molecular weight distribution (MWD) of the oligo(vinylformamide) (OVFA) were investigated by means of 1H NMR spectroscopy, matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), gel permeation chromatography (GPC), and combustion analysis. In all cases, OVFAs with narrow MWD were obtained in moderate yield (5–50%) in the temperature range from 253 to 313 K. A reaction temperature below 253 K is not suitable for the cationic polymerization of VFA because no oligomeric products are obtained. The properties and chemical constitution of the OVFAs, such as the average molecular weight, yield, and the chain structure are strongly determined by the reaction temperature used. With increasing reaction temperature the head group functionality decreases and the yield of OVFA increases. The correspondence between the results of quantum chemical calculations with those of the experiments is discussed.