The living cationic ring-opening polymerizations of 2-methyl-, 2-ethyl-, 2-nonyl-, and 2-phenyl-2-oxazoline were performed in acetonitrile at high temperatures of up to 200 degrees C in a single-mode microwave reactor. Upon enhancing the reaction rates by factors of up to 400 in the range from 80 to 200 degrees C, the first-order kinetics of the monomer consumption and the livingness of the polymerization were maintained. As a consequence of the fast, direct, and noncontact heating by the microwave irradiation, the polymerizations could be carried out in highly concentrated solutions or even from bulk conditions, yielding well-defined polymers (PDl < 1.20). Under the conditions applied in this study, a maximum number of 300 monomers (100 in the case of 2-methyl- and 2-nonyl-2-oxazoline) could be incorporated into the polymer chains under the premise that the average molecular weight distributions remained narrow (PDI < 1.20).