Mechanical and Gas Barrier Properties of Structurally Enhanced Poly(ethylene terephthalate) by Introducing 1,6-Hexylenediamine Unit

1,6-Hexylenediamine (HMDA) was chosen to replace part of ethylene glycol to develop a novel poly(ethylene terephthalate) structure with amide bonds. Four kinds of poly(ester amide)analogues (p-ETA) with different contents of amide bonds (1-4 mol %) were successfully synthesized via a new simple synthesis procedure. It was proved that the thermal stability and mechanical properties were significantly enhanced because of the introduction of amide bond units. More importantly, adding a small amount (1 mol %) of HMDA could effectively accelerate the orderly arrangement of molecular chains and formation of crystal nuclei proved by differential scanning calorimetry, X-ray diffraction, and polarized optical microscopy test results. It showed that the calendered p-ETA films acted as a good barrier to water and oxygen, expanding its application as packaging materials. Experimental results indicated that the introduction of amide bond units substantially promoted the overall performances of poly(ethylene terephthalate), such as crystallinity (28.4 vs 14.1%), tensile strength (60.9 vs 55.7 MPa), elongation at break (381 vs 226.8%), and so forth.