Synthesis of statistical poly(ethylene terephthalate-co-2,6-naphthalate) (co)polymers and study on their properties: Thermal and barrier properties

In this paper, a series of poly(ethylene terephthalate-co-2,6-naphthalate) (PETN) (co)polyesters with different naphthalene ring contents were synthesized via a two-step transesterification and polycondensation. The effects of the monomer compositions on the sequence distribution, crystallization, mechanical, thermal, and barrier properties of the (co)polymers were investigated systematically. The results showed that the introduction of naphthalene ring units (NDC) changed the sequence length of the PETN and disrupted the orderly arrangement of the PETN molecular chains, thus affecting the aggregated structure and properties of the copolymer. When the NDC content was less than 30%, the PETN copolymers displayed good ductility and higher yield strength comparable to PET, and the heat distortion temperature (HDT), thermal stability properties, and barrier properties of the copolymer were also improved. In addition, the diffusion kinetics of water and oxygen molecules in the (co)polymer were investigated by the MS program simulation software. The differences in gas barrier properties of the different PETN (co)polymers were explained at the molecular level. This study provides a systematic theoretical basis and comprehensive practical guidance for the preparation of high-performance copolyester materials.