Structure-Property Relationships of Ionic Poly(ethylene terephthalate) (PET): Effect of Ion Content and Species

Abstract

The functionalization of poly(ethylene terephthalate) (PET) is potential to expand applications of PET, particularly in high-value-added fields. To address the limitations of low ionic content of traditional anionic PET, this study employs sodium dimethyl isophthalate-5-sulfonate (SIPM) as the ionic monomer, and the copolymer was synthesized by transesterification and polycondensation. Ethylene glycol (EG) or butanediol (BDO) was applied to react with SIPM to obtain different ionic types of SIPE or SIPB. The ionic monomers are introduced into the PET macromolecular chains by the reaction between dimethyl terephthalate (DMT), EG, and SIPE or SIPB, and for the first time, the effect of ion types and contents on PET on properties was systematically studied. The incorporation of ionic groups led to a notable enhancement in mechanical, thermal, and hydrophilic properties of PET ionomers. The introduction of SIPB effectively improves the elongation at break and impact strength of PET, while the incorporation of SIPE substantially enhances the tensile and flexural strength of PET. Furthermore, an increase in ion content evidently improves hydrophilicity of the PET ionomer, with maximum water absorption of 30% and lowest water contact angle of 67°. With the introduction of the ion group, the macromolecular chain's regularity is disrupted, and the crystallinity of PET ionomers is reduced, which is promising to increase its transparency. Consequently, PET exhibits great potential to be applied in packaging materials, textile industry, and optical field.