Preparation of bio-based high heat-resistant copolyesters based on furan dicarboxylic acid and fluorene monomers

Partially bio-based PECBF copolyesters were synthesized from FDCA, BPEF, CHDM and EG. • The copolyesters turn fully amorphous above 10 mol% BPEF, with lower softening and processing temperature than those of PEN/PCTT. • PECBF15 combines a Tg of 100 °C, 68 MPa strength, 65% elongation and <5% haze. Commercial polyesters such as PET and PBT suffer from limited heat resistance, while the heat-resistant PEN and PCTT demand high processing temperatures, and are fully petroleum-based. The bio-based alternative PEF combines only a modest glass transition temperature with pronounced brittleness. Herein, partially bio-based, highly heat-resistant PECBF copolyesters were synthesized from dimethyl furan-2,5-dicarboxylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (BPEF), 1,4-cyclohexanedimethanol and ethylene glycol via transesterification–melt polycondensation (M n = 36,000–49,500 g/mol, Đ = 1.47–1.75). Quantitative 13 C NMR sequence analysis reveals a random but non-ideal comonomer distribution in which BPEF units are preferentially isolated (L n ,BF = 1.1–1.3 even at ≥ 20 mol% BPEF), suppressing consecutive BFB sequences. The copolyesters turn fully amorphous above 10 mol% BPEF, while the glass transition temperature rises from 82 to 115 °C and the Vicat softening temperature from 90 to 117 °C, with 5 % weight-loss temperatures above 365 °C. The PECBF15 and PECBF30 show lower processing temperatures than PET, and afford high transparency (>82 %) and low haze (< 5 %). At 15 mol% BPEF, the copolyester combines a T g of 100 °C with a yield strength of 68 MPa and an elongation at break of 65 %, reconciling heat resistance, toughness, melt processability and transparency. With heat resistance approaching that of PCTT and PEN, substantially lower processing temperatures and a partially bio-based constitution, these PECBF copolyesters show promise as potential candidates for applications requiring heat-resistance and transparency with moderate optical scattering. Download: Download high-res image (150KB) Download: Download full-size image