Abstract
Ionic propagation of 2-alkenyl-2-oxazolines has been examined in the presence of both cationic and anionic initiators. In order to provide a basis for understanding the cationic (Brønsted acid) propagation modes, model systems involving 2-alkenyl-2-oxazolinium salts and nucleophiles were studied. Spectroscopic analysis of these salts (13C and 1H NMR) predicted electrophilic activity at the 2- and 5-position of the heterocyclic ring as well as the terminal olefin carbon. Nucleophilic attack was observed at each of these positions with specificity as a function of the nucleophile type. Ketene aminal species were demonstrated to be key intermediates in the cationic propagation processes as determined by deuterium trapping experiments. Three new cationic propagation modes leading to dimeric or oligomeric products were identified and occurred as a function of the (a) acid strength, (b) proton multiplicity of the acid, and (c) nucleophilicity of the polymerization medium. Proposed propagation mechanisms are discussed. Anionic polymerization of 2-isopropenyl-2-oxazoline with butyllithium was shown to give low-molecular-weight polymers which are identical to those obtained by use of radical initiators. Finally, this study demonstrates that whereas radical and anionic polymerization of 2-alkenyl-2-oxazolines involve α-carbon propagating species, the cationic modes proceed via β-carbon-type species.
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Tomalia, D., Thill, B. & Fazio, M. Ionic Oligomerization and Polymerization of 2-Alkenyl-2-oxazolines. Polym J 12, 661–675 (1980). https://doi.org/10.1295/polymj.12.661
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DOI: https://doi.org/10.1295/polymj.12.661