Two alkyl ketene oligomers (AKOs) with almost 100% purities were prepared in high yields of 80–90% from palmitic acid chloride and alkyl ketene dimer (prepared from palmitic acid chloride) in the presence of amine promoters. Two AKOs thus obtained had quite similar molecular weights (1000–10,000), carbon/hydrogen contents, X-ray diffraction patterns, solution-state 13C-NMR spectra, and water-contact angles. However, two AKOs had different size-exclusion chromatograms, differential scanning calorimetric curves, FTIR spectra, and solution-state 13C-NMR spectra for 13C-labeled AKOs. Based on the 13C-NMR spectra of 13C-unlabeled AKOs, AKOs are likely to have cyclic structures, thus having the limited molecular weights of <10,000. The results of FTIR spectra and 13C-NMR spectra of 13C-labeled AKOs indicated that three different repeating units were linked with various molar ratios and various connection patterns and combinations, constituting the cyclic AKOs. As a result, 13C-NMR spectra of 13C-labeled AKOs showed quite a number of carbon signals due to various 13CO and 13CC structures present in AKOs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3668–3673, 2013
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