Fully bio-based polyesters poly(ethylene-co-1,5-pentylene 2,5-thiophenedicarboxylate)s (PEPTs) with high toughness: Synthesis, characterization and thermo-mechanical properties

Highlights

• A series of bio-based copolyesters were synthesized from 2,5-thiophenedicarboxylic acid, 1,5-pentanediol and ethylene glycol.

• The effects of composition on microstructures, thermal properties, and mechanical properties were investigated.

• PeDO with five methylenes can appropriately decrease the glass transition temperature of PETF.

• PEPT29 exhibits high tensile strength (56.8 MPa), elongation at break (550%) and glass transition temperature (45.5 °C).

Abstract

The bio-based monomer 1,5-pentanediol (PeDO) was incorporated into poly(ethylene 2,5-thiophenedicarboxylate) (PETF). A series of poly(ethylene-co-1,5-pentylene 2,5-thiophenedicarboxylate)s (PEPTs) with various PeDO content (M_w > 30 000 g mol⁻¹) were readily synthesized. DSC results indicated that PETF and PEPT13 were crystalline polyesters, but other PEPTs were amorphous polymers. With the content of PeDO, the elongation at break gradually increased due to the introduction of the more flexible diol. When the content of PeDO was 29%, PEPT29 exhibits high tensile strength (56.8 MPa) and elongation at break (550%). Meanwhile, the glass transition temperature (45.5 °C) was still higher than the room temperature.

Introduction

In the recent years, with the rapid development of economy and the decline of oil reserves, the development and utilization of renewable resources is becoming more and more important. Bio-based materials derived from renewable resources have become an important hot spot of current polymer materials due to environmental protection [[1], [2], [3], [4], [5], [6], [7]]. Various bio-based monomers have been used for the synthesis bio-based polyesters [[8], [9], [10], [11]].

Until now, a lot of bio-based diols have been developed, such as ethylene glycol (EG) and 1,3-propanediol (PDO) and 1,4-butanediol (BDO) [12,13]. However, the research about bio-based diacids is relatively slow. Although bio-based succinic acid and sebacic acid have achieved industrialization, bio-based diacids with a rigid structure are rare.

2,5-Furandicarboxylic acid (FDCA) is a member of the furan family and can be obtained from renewable resources. There are two main synthetic routes for FDCA. 1. FDCA was synthesized by the oxidation of 5-Hydroxymethylfurfural (HMF) [14]. HMF can be obtained from fructose. Fructose is widely found in nature, such as fruits, melons and so on. 2. FDCA can be also obtained by the reaction of 2-furoic acid and CO₂ [[15], [16], [17]]. 2-Furoic acid is obtained by the oxidation of 2-furaldehyde derived from corn cob. This synthetic route can avoid competition with the food chain and consume greenhouse gas CO₂. FDCA-based polyesters, polyamides and polyurethanes have been synthesized [[18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]]. 2,5-Thiophenedicarboxylic acid (TDCA) is a similar compound of FDCA and can be obtained by the reaction of bio-based adipic acid and sulfoxide chloride [29]. TDCA can also be synthesized from fructose and the yield is about 50% [30]. Some TDCA-based polyesters have been synthesized [[31], [32], [33], [34], [35], [36], [37], [38]]. FDCA-based polyesters and TDCA-based polyesters exhibit excellent barrier properties. Compared with FDCA-based polyesters, TDCA-based polyesters showed better moisture barrier properties due to the higher dipole moment associated to furan ring and plasticizer effect of water in case of FDCA-based polyesters [34].

In previous studies, we have synthesized poly(ethylene 2,5-thiophenedicarboxylate) (PETF) derived from TDCA and EG. PETF exhibits a tensile strength (71.7 MPa) comparable to PET, but low elongation at break (24%).To improve PETF's toughness, CHDM is used to reduce the secondary transition temperature of PETF by us [38]. When the content of 1,4-cyclohexanedimethanol (CHDM) is equal to 29%, PECTF29 exhibits high elongation at break (208%). However, CHDM can be produced by the hydrogenation of dimethyl terephthalate (DMT) and DMT is derived from petroleum.

1,5-Pentanediol (PeDO) can be synthesized by hydrogenation of 1,5-pentanedioic acid and high yields (71%) was achieved [39]. Johannes G. de Vries reported a synthesized method of PeDO from valerolactone with a yield greater than 99% [40]. With the development of biological technology, PeDO can also be obtained from furfural derived from biomass [[41], [42], [43]]. Therefore, PeDO is a bio-based monomer (Scheme 1).

Previously, bio-based poly(ethylene 2,5-thiophenedicarboxylate) (PETF) had been synthesized from 2,5-thiophenedicarboxylic acid (TDCA) and ethylene glycol (EG) by us. However, PETF exhibits a low elongation at break (~24%) due to the high glass transition temperature and the suppressed thiophene ring-flipping. Copolymerization is a valid approach to improve the properties of PETF. 1,5-Pentanediol (PeDO) is an odd-carbon aliphatic diol derived from biomass. Recent studies by our group find that poly(1,5-pentylene 2,5-thiophenedicarboxylate) (PPeTF) is a kind of ductile plastic with high elongation at break (2200%) [36]. PeDO-based polyesters are not easy to crystallize due to the odd effect. Meanwhile, PeDO with five methylenes can also appropriately decrease the glass transition temperature of PETF. Thus, PeDO is especially suitable for improving the performance of PETF.

In this study, to improve the toughness of PETF, PeDO was introduced as a comonomer. A series of fully bio-based TDCA-based copolyesters were prepared. The chemical, physical and thermal properties of poly(ethylene-co-1,5-pentylene 2,5-thiophenedicarboxylate)s (PEPTs) were studied by FT-IR, ¹H NMR, ¹³C NMR, DSC, and TGA. Meanwhile, the mechanical properties of PEPTs are also tested.