Biobased aliphatic polyesters from a spirocyclic dicarboxylate monomer derived from levulinic acid. Issue 15 (20th July 2021) - Valsange, Nitin G.
Abstract : Ethyl levulinate is readily ketalized with biobased pentaerythritol to form a spirocyclic diester monomer with low GHG emissions to produce a series of fully aliphatic processable polyesters. Abstract : Levulinic acid derived from lignocellulose is an important biobased building block. Here, we report on the synthesis and polymerization of a rigid spirocyclic diester monomer to produce polyesters and copolyesters. The monomer was prepared via a one-step acid catalyzed ketalization involving ethyl levulinate and pentaerythritol by employing a straightforward, solvent-free, and readily scalable method which required no chromatographic purification. Still, careful removal of traces of water from the spiro-diester prior to polycondensations proved crucial to avoid side reactions. A preliminary life cycle assessment (LCA) in terms of greenhouse gas (GHG) emissions indicated that the corresponding spiro-diacid tended to be environmentally favourable, producing less CO2 emission than e.g., biobased succinic acid and adipic acid. A series of aliphatic polyesters with reasonably high molecular weights was subsequently prepared in melt and modified melt polycondensations of the spiro-diester with 1, 4-butanediol, 1, 6-hexanediol, neopentyl glycol and 1, 4-cyclohexanedimethanol, respectively. The resulting fully amorphous polyesters showed glass transition temperatures in the range 12–49 °C and thermal stability up to 300 °C. Hot-pressed films of the polyesters based on neopentyl glycol and 1, 4-cyclohexanedimethanol were transparent and mechanically strong, and dynamic melt rheology showed stable shear moduli over time to indicate good processability. In addition, the spiro-diester monomer was employed in copolycondensations with diethyl adipate and 1, 4-butanediol and demonstrated good reactivity and stability. Hence, the results of the present study indicate that the spiro-diester based on levulinic acid is an effective monomer for the preparation of aliphatic polyesters and other condensation polymers.