Unsaturated Polyester Resins from a Biobased Furfural-Derived Sulfur-Bridged Difuran Monomer

Furfural-derived dimethyl 5,5′-sulfanediyldi(furan-2-carboxylate) (dm-SFA) and biobased fumarate (dm-FA) enable the preparation of partially biobased resins (UPRs) with commercial-level performance. Novel unsaturated polyesters (UPs) were synthesized via titanium-catalyzed polycondensation using the dm-SFA monomer, unsaturated dm-FA, and two commonly used diols: 1,2-propanediol and diethylene glycol. With the goal of achieving comparable or improved material properties to a fossil-based commercial UPR, the prepared UPs were cross-linked using fossil-based styrene as a reactive diluent with a UP-to-styrene ratio of 62:38 w/w. The most optimal material properties were achieved by using diethylene glycol as the sole diol (FA60:SFA40-DEG100; NOROX), resulting in a UPR with a high glass transition temperature (98.0 ± 0.4 °C, 2% lower compared to the commercial reference), excellent tensile strength (71.9 ± 3.7 MPa, 76% higher compared to the commercial reference), and overall comparable material properties to the commercial reference. As UPRs are mostly utilized as binders in the composite industry, resin processability was also taken into consideration, keeping the resin viscosity at a moderate level (3.74 Pa·s).