Copolymers of Poly(ethylene terephthalate) (PET) were synthesized by the melt polymerization of terephthalic acid (TPA) with ethylene glycol (EG) and with each of the active oxygen scavengers; monoolein (MO) and 3-cyclohexene-1,1-dimethanol (CHEDM) in separate compositions. Proton nuclear magnetic resonance spectroscopy (1H NMR) and 2D correlation spectroscopy (COSY) indicated that PET had reacted with both MO and CHEDM at their hydroxyl end groups. Oxygen barrier properties of the MO and CHEDM copolymers exhibited improvements of up to 40%, in comparison to an unmodified commercial PET. Effects of the oxygen scavengers on the copolymers' physical properties were investigated in terms of their crystallization, melting, and rheological behaviors. Both types of copolymers showed decreases in peak melting temperatures with increased scavenger concentrations and also crystallized more slowly as the scavenger concentrations increased. The PET/MO copolymer showed non-Newtonian rheological behavior with higher MO concentration; while the PET/CHEDM copolymers showed Newtonian behavior within the studied range of CHEDM concentrations. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013