Isomerization polymerization of 2-oxazoline: I. Preparation of unsubstituted 2-oxazoline polymer

Abstract

Pure unsubstituted 2-oxazoline (OXZ) was first prepared in good yields by modifying Wenker's method. OXZ was found to polymerize by cationic catalyst in an aprotic polar solvent to give a solid polymer. The polymerization of OXZ in less-polar solvents gave polymer in much decreased yields. Lewis acids such as BF3OEt2 and SbF5, sulfonates, sulfate esters, mineral acids, and alkyl iodide were effective as the polymerization catalyst. But metal chlorides such as SnCl4 and SbCl5 were ineffective. The polymer was a white powder, which was soluble in water and insoluble in most organic solvents. The polymer was shown to be crystalline by X-ray diffraction diagram (nap ca. 210°C). The molecular structure of the polymer proved to be poly(N-formylethyleneimine) by NMR and IR spectra. Alkaline hydrolysis of poly-OXZ gave crystalline polyethyleneimine (mp 58.5°C).