Cyclic alkyl ketene oligomers

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 ¹³C?O and ¹³C?C structures present in AKOs. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3668–3673, 2013