Cellulose Dissolution and In Situ Grafting in a Reversible System using an Organocatalyst and Carbon Dioxide.

Cellulose is a promising renewable material, but cannot easily be processed homogeneously owing to the stiffness of the molecules and the dense packing of its chains, due to intermolecular hydrogen bonds. Cellulose processability can be improved by chemical modification. The reversible reaction of cellulose with carbon dioxide in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) allows dissolution of cellulose in dimethyl sulfoxide (DMSO). This DMSO solution is an effective medium for grafting L-lactide (LLA) from cellulose by ring-opening polymerization (ROP) under mild conditions, allowing to prepare cellulose-graft-poly(L-lactide) co-polymers with a molar substitution (MSPLLA ) of poly(L-lactide) in the range of 0.37-5.32, at 80 °C. This makes DBU not only an important reagent to achieve cellulose dissolution, but it also acts as organocatalyst for the subsequent ring-opening polymerization process. Characterization of the structure and thermal properties of the co-polymers by a variety of techniques reveals that they have a single glass-transition temperature (Tg ), which decreases with increasing MSPLLA . Thus, the modification results in a transformation of the originally semirigid cellulose into a thermoplastic material with tunable Tg . The carbon dioxide dissolution strategy is an efficient platform for cellulose derivatization by homogeneous organocatalysis.