13C NMR study of O‐(2‐hydroxypropyl)cellulose

Abstract

AbstractThe proton‐decoupled signal of methyl carbons of O‐(2‐hydroxypropyl)cellulose (HPC) (1b, m ≥ 1) was found to be split into two peaks. The results of experiments on lanthanide shift and the dependence of the relative intensities of both peaks on the molecular weight of poly(oxypropylene) [poly(propylene oxide)] (PPO) indicated that the low‐field peak results from the terminal hydroxypropyl groups and the high‐field peak from the inside oxypropylene units. From the ratio between the intensities of the two peaks and the molar substitution (MS) (average number of oxypropylene units per anhydroglucose (AHG) unit), the degree of substitution (DS) (average number of hydroxyl groups substituted per AHG unit) was calculated. This new method could be applied to samples of low‐MS to which the conventional method based on the 1H NMR technique alone was inapplicable. From the analysis of 13C NMR spectra of HPC samples differing in MS, an authentic structural picuture of the HPC molecule could be proposed.