An oligomer is a molecule that consists of a few monomer units. It can be formed during polymer manufacturing and also due to polymer degradation processes or even during use conditions. Since oligomers are not included in chemical databases, its identification is a complex process. In this work, the oligomers present in 20 different PET pellets samples have been determined. Two different sample treatment procedures, solvent extraction and total dissolution, were applied in order to select the most efficient one. The analyses were carried out by UPLC-MS-QTOF. The use of high resolution mass spectrometry allowed the structural elucidation of these compounds and its correct identification.The main oligomers identified were cyclic as well as lineal from the first, second and third series. All of them were composed by terephthalic acid (TPA), diethylene glycol (DEG) and ethylene glycol (EG). Quantitative values were very different in both procedures. In total dissolution of PET samples, the concentration of oligomers was always, at least, 10 times higher than in solvent extraction, being some of the compounds only detected when total dissolution was used. Results showed that the oligomers with the highest concentration values were dimers and trimers, cyclic as well as lineal, from the first and second series. The oligomer with the maximum concentration value was TPA2-EG-DEG, that was found in all the samples in a concentration range from 2493 to 19290 ng/g PET. No differences between virgin and recycled PET were found. Migration experiments were performed in 2 PET bottles, results showed the transference of most of these oligomers to a fat food simulant (ethanol 95%).

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Most multilayer high barrier materials used in food packaging have a polyurethane adhesive layer in their structures. In order to assess the safety of these materials, it is important to determine the compounds intentionally added to the adhesives (IAS) as well as those non-intentionally added substances (NIAS). During the manufacture of polyurethane adhesives, some by-products can be formed, such as cyclic polyester oligomers coming from the reaction between dicarboxylic acids and glycols. Since these compounds are not listed in the Regulation 10/2011/EU, they should not be found in migration above 0.01 mg/kg of simulant. In this study two flexible multilayer packaging materials were used and migration was evaluated in simulant A (ethanol 10% v/v), simulant B (acetic acid 3% w/v) and simulant ethanol 95% v/v during 10 days at 60ºC. Identification and quantification of non-volatile compounds was carried out by UPLC-MS-QTOF. Most of migrants were oligomers such as cyclic polyesters and caprolactam oligomers. Overall migration and specific migration of adipic acid-diethylene glycol and phthalic acid-diethylene glycol were monitored over time and analysed by UPLC-MS-TQ. In most cases, ethanol 95% v/v was the simulant with the highest concentration values. Overall migration kinetics followed a similar pattern than specific migration kinetics.

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