Vinylformamide (VFA) is cationically polymerized in various solvents at 273 K and reaction temperature by the following initiators: iodine, bis(4‐methoxyphenyl)‐methyl chloride/silica, triphenylmethyl chloride/silica, and trimethylsilyl triflate. In every case defined oligomers with narrow molecular weight distribution are obtained in moderate yield (20–50%). Acid hydrolysis of the obtained oligomers yields well defined oligovinylamine products. The cationic initiation mechanism of VFA is discussed in terms of the HSAB‐concept

No abstract

A critical review of former investigations on the cationically induced oligomerization of N-vinylformamide points out that some of the results are not in agreement with the model of an cationic propagation mechanism. Special attention in the discussion of the results is given on the chain structure of the oligo(N-vinylformamide)s. In comparison with N-vinylformamide, the ability of different N-vinylamides to undergo a cationically induced polymerization to oligomeric products was investigated. Only the secondary N-vinylamides, N-vinylformamide (VFA) or N-vinylacetamide (VAcA), readily form higher oligomers with various cationic initiators. N-Methyl-N-vinylformamide and the cyclic N-vinylpyrrolidone (VP) dimerize with acidic catalysts, whereas N-methyl-N-vinylacetamide gives a mixture of low molecular products. The N-alkyl-substituted N-vinylamides are not able to undergo a oligomerization to higher oligomers (M n > 200) under the conditions investigated. The cationic polymerization of N-deutero-N-vinylformamide (VFAD) and the 2H NMR analysis of the obtained oligomers show that the nitrogen-bonded hydrogen (deuterium) is strongly involved in the proton transfer as well as the propagation reaction. From these results, we propose an alternative oligomerization mechanism for the oligomerization of secondary N-vinylamides. A nonionic pericyclic transition state is potentially suggested involving a N-formylimine end group and the monomer rather than a cationically active chain.

SUMMARY: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 C2C 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 1 H 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.

No abstract