Cornelis Post

Selective hydrogenation is a crucial process in the synthesis of chemical intermediates. Here, we report the efficient hydrogenation of 5-hydroxymethylfurfural (HMF) to 2,5-bishydroxymethylfuran (BHMF) over N-doped C-supported cobalt catalysts (CoNC) derived from ZIF-67 for the enzymatic synthesis of poly(2,5-furandimethylene adipate) (PFAd). By varying the oxidative pretreatment temperature, a series of CoNCX catalysts (where X denotes the oxidation temperature) were obtained, enabling effective tuning of catalytic activity. The optimized catalyst, CoNC200, achieved 93% HMF conversion and 99% BHMF selectivity, with a BHMF yield approximately 30% higher than that of the nonoxidized sample at 100 °C within 20 min. Notably, near-complete conversion and high selectivity can be achieved at room temperature within 8 h, while similar performance is obtained at 120 °C within 30 min, demonstrating high selectivity and efficiency across a wide temperature range. The low apparent activation energy (39.9 kJ mol–1) further confirms the high intrinsic activity of CoNC200. The enhanced low-temperature performance is attributed to the synergistic effect of CoOOH and Co3O4 species with high-valence cobalt sites on the N-doped carbon support, as revealed by comprehensive characterization. Furthermore, the catalytic system is compatible with enzymatic polymerization, enabling direct conversion of crude BHMF mixtures containing residual HMF into polyesters using dimethyl adipate. The presence of HMF allows modulation of the polymer molecular weight without compromising the thermal properties. These findings underscore a robust and versatile strategy for integrating selective hydrogenation with mild enzymatic polycondensation toward bio-based polyesters.

Overview of the enzymatic synthesis of various biobased and biodegradable (co)polyesters derived from BHMTHF, dimethyl adipate, BHMF, and FDCA.

Conversion of cyclic renewable monomers derived from camphoric acid and CHDM into biobased polyesters with tunable thermal and structural properties.

BHMTHF, also known as THFDM, is a biobased monomer that is utilized in the synthesis of polyesters and polyurethanes with unique properties. This review highlights the synthesis and structure-property relationship of these interesting polymers.

2,5-Bis(hydroxymethyl)furan (BHMF)-based polyesters are an interesting new class of biobased and potentially biodegradable furanic polymers. However, their thermal properties are currently insufficient, making them unsuitable for potential applications as commodity plastics. To improve this, several polyesters were synthesized using an enzymatic bulk polymerization process with the monomers BHMF and aliphatic dimethyl esters of varying spacer lengths. The BHMF units were subsequently cross-linked with a biobased bismaleimide (BM-689) through a [4 + 2] cycloaddition reaction between the furan and maleimide groups. This approach clearly demonstrated that these furan-based polyesters can be thermoreversibly cross-linked using this bismaleimide. The use of different spacer lengths further allows the variation in relative reaction rates and affects the reversibility and reprocessability of the polymers. In situ ¹H NMR spectroscopy revealed the identification of the endo- and exostereoadducts formed by the Diels-Alder reaction. A rheological analysis demonstrated the reprocessability and the thermal properties were further characterized via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). This study sheds light on the thermal and mechanical enhancement of biobased BHMF-based polyesters, while maintaining their recyclability, which widens the range of potential application of this promising polymer.

BHMF-based polyesters are synthesized via enzymatic bulk polymerization. The thermal, mechanical and rheological properties can be tuned by varying the structural composition of the polymer, which also influences the biodegradation rate.