On the way to greener furanic-aliphatic poly(ester amide)s: Enzymatic polymerization in ionic liquid

Abstract

The polymerization of 2,5-furandicarboxylic acid (FDCA), one of the key building blocks for the preparation of furan polymers, is often accompanied with side reactions (e.g. decarboxylation). Due to the mild reaction conditions, enzymatic polymerizations became an excellent candidate to address this issue. Here, we present a green and effective method to prepare different furanic-aliphatic poly(ester amide)s (PEAFs) by applying two different approaches. PEAFs with Mw‾ up to 21 kg mol−1 were successfully synthesized by a Novozyme 435-catalyzed polycondensation of dimethyl 2,5-furandicarboxylate (DMFDCA) with aliphatic diols, diamines or amino alcohols, using toluene at 90 °C. Additionally, we were able to enhance the sustainability of the entire process by performing the polymerization in ionic liquids – BMIMPF6 and EMIMBF4. Using the ionic liquids (ILs) BMIMPF6 and EMIMBF4 as solvents, we were able to produce PEAFs with Mw‾ up to 7 kg mol−1. The different polarity of the solvents affects the enzyme activity and product solubility, thus also the final molecular weight of the PEAFs. Despite the lower molecular weight, the tested ILs result products with similar characteristics. All obtained PEAFs are semi-crystalline materials and decompose at a temperature around 390 °C with a Tm of around 77–140 °C and Tg of around 11–46 °C. Although still exemplified on the proof-of-concept production of sustainable materials, these findings pave the way to promote the transition from fossil-to bio-based polymers, as well as more environmentally friendly synthetic routes.