High performance sulfur-containing copolyesters from bio-sourced aromatic monomers

Abstract

In this investigation, a series of novel random bio-based thiophene–aromatic copolyesters, including thiophene and phenyl units, were successfully prepared from dimethyl 2,5-thiophenedicarboxylate, dimethyl 2,5-dimethoxyterephthalate, and the aliphatic diols ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and 1,8-octanediol, via twostep melt polymerization as a facile and green semi-continuous process. Techniques used to monitor the polymerization process included Fourier transform infrared (FTIR) and proton nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC), differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. The copolymers had tunable Tg values ranging from 47–120°C, while their 5% decomposition temperature (Td, 5%) under N2 varied from 405–370 °C. GPC analysis showed that the polyesters had weight-average molecular weights (Mw) of 41 400–48 500 g/mol and polydispersity indices of 1.47–2.24. A study of structure-property relations showed that the properties of these copolymers can be tailored by varying their composition. All the copolyesters exhibited high tensile strength (45–80 MPa) and toughness values (elongation at break of 200–540%). After 28 weeks of incubation in humid soil, weight losses of up to 7.2% were observed. Considering their good mechanical properties, thermal stability and biodegradability, these renewable sulfur-containing copolyesters have great potential to replace petroleum-based commercial poly(ethylene terephthalate) in the food packaging industry, which is helpful to implement carbon neutrality and sustainable development in the polymer industry.

Keywords

• biodegradable polymers
• aromatic monomers
• aliphatic diols
• mechanical properties
• melt transesterification