The bio-based polyester, poly(ethylene 2,5-furandicarboxylate) (PEF), was modified by 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) via copolymerization and a series of copolyesters poly(ethylene-co-2,2,4,4-tetramethyl-1,3-cyclobutanediol 2,5-furandicarboxylate)s (PETFs) were prepared. After their chemical structures and sequence distribution were confirmed by nuclear magnetic resonance (H-1-NMR and C-13-NMR), their thermal, mechanical, and gas barrier properties were investigated in detail. Results showed that when the content of CBDO unit in the copolyesters was increased up to 10 mol%, the completely amorphous copolyesters with good transparency could be obtained. In addition, with the increasing content of CBDO units in the copolyesters, the glass transition temperature was increased from 88.9 degrees C for PET to 94.3 degrees C for PETF-23 and the tensile modulus was increased from 3000 MPa for PEF to 3500 MPa for PETF-23. The barrier properties study demonstrated that although the introduction of CBDO units would increase the O-2 and CO2 permeability of PEF slightly, PECF-10 still showed better or similar barrier properties compared with those of PEN and PEI. In one word, the modified PEF copolyesters exhibited better mechanical properties, higher glass transition temperature, good barrier properties, and better clarity. They have great potential to be the bio-based alternative to the popular petroleum-based poly(ethylene terephthalate) (PET) when used as the beverage packaging materials. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3298-3307