Synthesis and Properties of Copolyesters Derived from 1,4-Cyclohexanedimethanol, Terephthalic Acid, and 2,6-Naphthalenedicarboxylic Acid with Enhanced Thermal and Barrier Properties

Abstract

In this work, a series of poly(1,4-cyclohexylenedimethylene terephthalate-co-1,4-cyclohexylene dimethylene 2,6-naphthalenedicarboxylate) (PCTN) copolymers with different compositions of two diacids: terephthalic acid (TPA) and 2,6-naphthalenedicarboxylic acid (NDA), and stoichiometry matched 1,4-cyclohexanedimethanol (CHDM) were synthesized directly by a melt polymerization technique. Thermal properties of synthesized copolymers were measured by a differential scanning calorimetry (DSC). The incorporation of either NDA or CHDM improved the glass transition temperature (T g) of PCTN compared to poly(ethylene terephthalate) (PET). Thermal degradation behaviors were analyzed using a thermogravimetric analysis (TGA). Chemical structures of the obtained copolyesters were investigated by a nuclear magnetic resonance spectroscopy (1 H NMR). Our results showed that the thermal and optical properties (determined by UV-Vis spectrophotometer) of the PCTN copolyesters were directly dependent on the ratio of TPA and NDA. It was also found that PCTN films have superior optical, thermal, and barrier (reduced water absorption) properties than PET and poly(ethylene naphthalate) (PEN) films.

Structure–property relationship of poly(cyclohexane 1,4‐dimethylene terephthalate) modified with high trans‐1,4‐cyclohexanedimethanol and 2,6‐naphthalene dicarboxylicacid

“…The molecular weights of all the synthesized copolyesters were determined using Mark‐Houwink's equation, and the results are summarized in Table . It is important to note that PC#TN copolyesters were having high enough molecular weights to be fabricated into the film, nanofiber, or any desired shape for the practical applications in versatile areas . It is also worthy to note that with a progressive increase in trans CHDM content, the molecular weight of the copolyester decreases, indicating that it becomes more difficult to get high‐molecular‐weight copolyesters using melt polymerization when relatively rigid and more stable trans‐CHDM isomer units are incorporated into the copolyester.…”

“…A series of PC#TN copolyesters were synthesized adopting a conventional two‐step melt polymerization technique . The pilot scale melt polymerization reactor used for the synthesis of PC#TN samples is shown in Figure .…”

“…and Fiaz et al . successfully tuned the processing window and resolved the high processing temperature problem by synthesizing a series of random copolyesters of PCT with the second diacid monomer . Sivaram et al .…”

“…Incorporation of a small amount of diacid into the polymer backbone effectively widens the processing window of PCT‐based polyester by lowering its T m . In our previous studies, we have successfully tuned the processing window of PCT by incorporating the second diacid moiety . An increasing amount of the second diacid effectively improves thermal stability, hydrolysis resistance, chemical resistance, mechanical, and barrier properties.…”

“…An increasing amount of the second diacid effectively improves thermal stability, hydrolysis resistance, chemical resistance, mechanical, and barrier properties. However, the very low molecular weight was obtained during solution polymerization and a higher amount of second diacids results in high cost, high birefringence, and processing issues during film fabrication …”