Green Polymer Precursors from Biomass-Based Levulinic Acid

Abstract

Levulinic acid (LA) has been identified as a suitable chemical feedstock that can be isolated from biomass. Its conversion into γ-valerolactone (GVL) via hydrogenation and ringclosure to the lactone has been studied as a versatile route to the manufacture of biodegradable polyesters. For hydrogenation of LA using Ru/C catalyst (the first method), conversion of LA at 100% was observed after 50min at 90¡C in water, with a GVL selectivity of 73%. The product selectivity may be steered by the temperature. At low temperatures 4-HVA is formed selectively, whereas higher temperatures favour the formation of GVL. Meanwhile in the second method, hydrogenation of LA using biphasic water soluble Ru-TPPTS catalysis made in situ in dichloromethane/water biphasic mixtures showed essentially quantitative GVL yields (82%) at 45bar, 90 ¡C and 60min reaction time (1% mol catalyst). As product of the LA hydrogenation, GVL has a very low reactivity for ring-opening due to a very low ring strain. Several studies therefore focused on GVL ring opening into polymerizable compounds but the results so far are unsatisfactory. In this work a novel route has been also investigated using amines for the ring-opening. Because of the basic properties, adding of amine compounds, such as ammonia, aminoethanol, ethylenediamine and piperazine has successfully converted the lactone into compounds containing two functional group viz. alcohol and amide, in essentially quantitative yields. Product design through varying the structure of the amine compound, such as backbone structure and presence of functional groups, appears to be a promising polymer engineering pathway. As such, the novel pathway delivered co-monomers for use in polymer synthesis, to manufacture possible green polymers.