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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 ( 1 H 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.

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Active barrier developments for poly(ethylene terephthalate) (PET) are among important approaches being used to achieve improvements in the polyester's barrier properties. This work utilized two active barrier materials and their PET copolymers, synthesized by melt polymerization of terephthalic acid (TPA) with ethylene glycol (EG) and active oxygen scavengers: monoolein (MO) or 3-cyclohexene-1,1-dimethanol (CHEDM), in separate compositions. The oxidizable monomers and their copolymers were characterized with respect to changes resulting from their reactions with oxygen. Evaluations of their infrared and nuclear magnetic resonance spectra established that the monomers as well as their PET copolymers underwent first order reactions and had rate constants ranging from 0.03 to 0.08 day 21 . The only volatile oxidation product of MO was acetaldehyde and no volatile products resulted from oxidation of CHEDM. In comparison to unmodified PET, the PET/MO and PET/CHEDM copolymers achieved respective oxygen barrier property improvements of about 30 and 40%. Results from this study have shown that the oxidation kinetics of pure monomers of this type may be used for evaluation of their effectiveness and suitability as active barrier materials, without the need to synthesize their corresponding PET copolymers. This is significant and work is continuing to include other moieties that will interact with higher levels of oxygen and react at faster rates.