Cyclic carbonate functionalized lignin as non-toxic intermediate for renewable polymers

Cyclic carbonate functionalized lignin could be an important step towards the development of renewable lignin-based polymers and the replacement of conventional fossil-based products. The cyclic carbonate based intermediates offer a favorable starting point for further reactions. A variety of functional groups such as carboxylic acids, amines and hydroxy groups are available as reaction partners for the cyclic carbonate terminus. This provides a wide spectrum of potential products and applications such as adhesives, foams, insulations and coatings. This study shows two synthesis pathways for producing non-toxic cyclic carbonate functionalized lignin as well as further reactions to lignin-based products. The first route consists of a solvent-free oxyalkylation of lignin in the first step and a trans-esterification with linear carbonates in the second step. The lignin-based cylic carbonate is obtained as powdery, solid material with yields of up to 95%. On the second route, multifunctional cyclic carbonates such as poly(ethylenglycol) dipropylene carbonate, trimethylolpropane tripropylene carbonate as well as a range of carbonated vegetable oils serve as solvent and reactant for lignin. A base catalyzed single step reaction leads to highly viscous fluids with increased molecular weights. All products were comprehensively characterized by FTIR, and NMR spectroscopy. These lignin-based resins contain multiple cyclic carbonate functionalities and are therefore suitable as prepolymers for further reactions. It could be shown that the cyclic carbonate functionalized lignins react with polyamines to form non-isocyanate-based systems with renewable and non-toxi carbamate products. Furthermore, the carbonate modified lignin prepolymers are used in various experiments as reactant for proteions, carbo-hydrates and other bio-based compounds to obtain renewable polymers. The product formation was examined by Differential Scanning Calorimetry (DSC), FTIR- and NMR specroscopy.