Preparation and characterization of cellulose beta-ketoesters prepared by homogeneous reaction with alkylketene dimers: comparison with cellulose/fatty acid esters

摘要

Cellulose was dissolved in lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI), and reacted with alkylketene dimers (AKDs) under non-aqueous and homogeneous conditions to prepare cellulose/AKD beta-ketoesters with high degrees of substitution (DS). Six AKDs synthesized from octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids via their fatty acid chlorides were used in this study. The cellulose/AKD beta-ketoesters obtained were gummy solid at room temperature, and had DS values ranging from 1.9 to 2.9. Cellulose/fatty acid esters with DS 2.5-2.9 were also prepared as references. C-13-NMR spectra of the cellulose/AKD beta-ketoesters showed that cellulose carbons and substituent carbons close to cellulose chains were restricted in motion and behaved like solid in solutions. In contrast, the cellulose/fatty acid esters did not demonstrate such anomalous C-13-NMR spectra. The unique C-13-NMR patterns are characteristic for the cellulose/AKD beta-ketoesters, which have long and branched alkyl substituents in each anhydroglucose unit. Size-exclusion chromatography furnished with multi-angle laser light scattering (SEC-MALLS) revealed, on the other hand, that all cellulose/AKD beta-ketoesters and cellulose/fatty acid esters prepared had flexible or random-coil conformations in tetrahydrofuran (THF). There were no clear differences in conformation or stiffness of cellulose chains between cellulose/AKD beta-ketoesters and cellulose/fatty acid esters.