To obtain furan-based copolyesters, a two-step polycondensation reaction was conducted in diphenyl ether with varying temperatures. The procedure involved the following steps: Initially, 2,5-DMFDCA, α,ω-aliphatic linear diol (α,ω-ALD), dilinoleic diol (DLD), and diphenyl ether (200 wt% of total monomers) were combined in a 100 ml three-necked round-bottom flask containing pre-dried CAL-B (10 wt% of total monomers). The mixture was magnetically stirred in an oil bath at 80 °C for 1 hour under an inert gas flow, aiming to achieve a homogeneous mixture. Subsequently, the temperature was increased to 95 °C, initiating the transesterification reaction. During this step, methanol was produced as a by-product and collected in a cold trap, which was adjusted to the neck of the round-bottom flask. This process lasted for 3 hours. After the transesterification, further oligomerization was carried out under a pressure of 600 Torr for 21 hours. The application of a mild vacuum in this step created a controlled environment that facilitated efficient oligomerization and prevented monomer loss caused by evaporation. Finally, a polycondensation reaction was performed at 95 °C under reduced pressure of 2 Torr for 24 hours, followed by an additional 48 hours at 140 °C.