Polymerization of 2-Oxazolines. I. Cationic Polymerization of 2-Phenyl-2-oxazoline Initiated by Various Oxazolinium Salts of Monomer with Brbnsted Acids

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Abstract
Various kinds of the complexes of 2-phenyl-2-oxazoline with various Bronsted acids were prepared. From the elementary analysis and spectroscopic analysis of the complex, it was identified to be an equimolar oxazolinium salt. The monomer could be polymerized with the oxazolinium salt to give N-benzoyl-polyethylenimine. The polymer yield in bulk polymerization was linearly proportional to the reaction time, and the number-average degree of polymerization of the polymer obtained at the complete conversion was proportional to the initial molar ratio of the monomer to the complex. The catalytic activities of the oxazolinium salts increased with a decrease in the pKavalue of Bronsted acid in water. The results of the infrared spectroscopy and nuclear magnetic resonance spectroscopy of the oxazolinium salt at room temperature and elevated temperature indicated that the change of the double bond character of the imino and ether linkages is brought about by the complexation. On the basis of these results, the mechanism of the polymerization was proposed.

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