AbstractSummary: Aromatic copolyesters containing bio‐based furanic units in the main chain were obtained by ester‐interchange reaction between poly(ethylene terephthalate) (PET) and poly[ethylene 5,5′‐isopropylidene‐bis(2‐furoate)] (PEF) at high temperatures in the bulk. Various copolyesters were synthesized by using PET/PEF mass ratios ranging from 90:10 to 50:50 and were characterized by 1H NMR, MALDI‐TOF MS, DSC, and TGA. PET/PEF block copolymers were formed in the first stage of reaction and then slowly randomized. The degree of randomness, determined by 1H NMR, was close to 1 after 2 h reaction. The randomization rate depended on the nature and the concentration of the end‐groups of starting homopolyesters and was much faster when a low molar mass hydroxy‐terminated PET was reacted.Reaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction.magnified imageReaction scheme showing the insertion of furanic units in copolyester chains by ester interchange reaction.