Structure Elucidation of Hydroxypropyl Cellulose Homogenously Prepared from NaOH/Urea Aqueous Solution

Hydroxypropyl celluloses (HPC) were homogenously synthesized by the reaction of cellulose with propylene oxide in NaOH/urea aqueous solution. Water-soluble HPC with molar degree of substitution (MS_NMR) in the range of 0.52~0.78 was prepared from microcrystalline cellulose, cotton linters, and spruce sulfite pulp. The structure of the HPC samples was characterized by means of FT-IR, NMR, gas chromatography (GC), and size exclusion chromatography (SEC) analyses. Three types of cellulose samples with different molecular weights were found to dissolve well in the NaOH/urea solvent with no obvious differences in reactivity and regioselectivity. The relative reactivity of hydroxyl groups in the glycosyl unit was in the following order: O-6 > O-2 > O-3. In addition, the results of the study indicated that the tandem reaction during hydroxypropylation could be ignored.