Sustainable functionalization of cellulose and starch with diallyl carbonate in ionic liquids

A functional and environmentally benign alkoxycarbonylation reagent, diallyl carbonate (DAC), was employed for the sustainable and catalyst-free allyloxycarbonylation of cellulose under homogenous conditions using 1-butyl-3-methylimidazolium chloride (BMIMCI) as a solvent. As a result of optimization studies of the reaction conditions and molar ratio of DAC, cellulose was successfully converted to cellulose allyl carbonate exhibiting degrees of substitution (DS) of 0.8-1.3. The optimized conditions were also applied to maize starch leading to a DS of 1.2, thus demonstrating the reproducibility and versatility of the established procedure. The obtained cellulose and starch allyl carbonates were thoroughly characterized by ATR-IR, H-1, C-13, and P-31 NMR spectroscopy as well as by size exclusion chromatography (GPC). Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A transparent thin film was produced from cellulose allyl carbonate and mechanical properties were examined by tensile strength measurements, showing 21.6 MPa of tensile strength with 40% elongation at break. Additionally, cellulose allyl carbonate was successfully modified via thiol-ene chemistry employing 1-butane thiol, resulting in a material with improved thermal properties, showing a thermal transition (T-g) at 84 degrees C. Furthermore, the reported methodology represents a step forward in terms of sustainability for carbohydrate and especially cellulose modification, since non-toxic reagents were used and BMIMCI as well as the excess of DAC could be recycled and reused for further reactions.