A facile method to synthesize high-molecular-weight biobased polyesters from 2,5-furandicarboxylic acid and long-chain diols

Modifications of Furan-Based Polyesters with the Use of Rigid Diols

The replacement of polymers derived from petrochemical resources has been a prominent area of focus in recent decades. Polymers used in engineering materials must exhibit mechanical strength and stiffness while maintaining performance through a broad temperature range. Most of the polyesters used as engineering materials are based on terephthalic acid (TPA) and its derivatives, which provide necessary rigidity to molecular chains due to an aromatic ring. Bio-based alternatives for TPA-based polyesters that are gaining popularity are the polyesters derived from 2,5-furandicarboxylic acid (FDCA). To broaden applicational possibilities, one effective way to achieve specific properties in targeted applications is to adjust the composition and structure of polymers using advanced polymer chemistry techniques. The incorporation of rigid diols such as isosorbide, 1,4-cyclohexanedimethanol (CHDM), and 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) should result in a greater stiffness of the molecular chains. This review extensively explores the effect of incorporating rigid diols on material properties through a review of research articles as well as patents. Moreover, this review mainly focuses on the polyesters and copolyesters synthesized via two-step melt polycondensation and its alterations due to the industrial importance of this method. Innovative synthesis strategies and the resulting material properties are presented.

Synthesis of Biobased Poly(butylene Furandicarboxylate) Containing Polysulfone with Excellent Thermal Resistance Properties

A synthetic biopolymer derived from furandicarboxylic acid monomer and hydroxyethyl-terminated poly(ether sulfone) is presented. The synthesis involves 4,4'-dichlorodiphenyl sulfone and 4,4-dihydroxydiphenyl sulfone, resulting in poly(butylene furandicarboxylate)-poly(ether sulfone) copolyesters (PBFES) through melt polycondensation with titanium-catalyzed polymerization. This facile method yields segmented polyesters incorporating polysulfone, creating a versatile group of high-temperature thermoplastics with adjustable thermomechanical properties. The PBFES copolyesters demonstrate an impressive tensile modulus of 2830 MPa and a tensile strength of 84 MPa for PBFES55. Additionally, the poly(ether sulfone) unit imparts a relatively high glass transition temperature (Tg), ranging from 36.6 °C for poly(butylene 2,5-furandicarboxylate) to 112.3 °C for PBFES62. Moreover, the complete amorphous film of PBFES exhibits excellent transparency and solvent resistance, making it suitable for applications, such as food packaging materials.

Development of furan-2,5-dicarboxylic acid (FDCA)-based organogelators

Organogels are used in a wide range of applications for which the development of new bio-based organogelators is highly desirable. While furan-2,5-dicarboxylic acid (FDCA) is a promising molecule for the synthesis of bio-based polyesters, it has never been used in the context of organogels. This study explores the possibility to design FDCA-based organogelators that self-assemble into fibrillar networks stabilized by hydrogen bonding. Gelation tests show the versatility of this gelator family with a wide variety of gelled liquids, especially apolar liquids. The structure of the gels was investigated by FTIR and CD spectroscopies, crystallography, powder X-ray diffraction and rheology.

Effect of Monomer Type on the Synthesis and Properties of Poly(Ethylene Furanoate)

This work aimed to produce bio-based poly(ethylene furanoate) (PEF) with a high molecular weight using 2,5-furan dicarboxylic acid (FDCA) or its derivative dimethyl 2,5-furan dicarboxylate (DMFD), targeting food packaging applications. The effect of monomer type, molar ratios, catalyst, polycondensation time, and temperature on synthesized samples' intrinsic viscosities and color intensity was evaluated. It was found that FDCA is more effective than DMFD in producing PEF with higher molecular weight. A sum of complementary techniques was employed to study the structure-properties relationships of the prepared PEF samples, both in amorphous and semicrystalline states. The amorphous samples exhibited an increase in glass transition temperature of 82-87 °C, and annealed samples displayed a decrease in crystallinity with increasing intrinsic viscosity, as analyzed by differential scanning calorimetry and X-ray diffraction. Dielectric spectroscopy showed moderate local and segmental dynamics and high ionic conductivity for the 2,5-FDCA-based samples. The spherulite size and nuclei density of samples improved with increased melt crystallization and viscosity, respectively. The hydrophilicity and oxygen permeability of the samples were reduced with increased rigidity and molecular weight. The nanoindentation test showed that the hardness and elastic modulus of amorphous and annealed samples is higher at low viscosities due to high intermolecular interactions and degree of crystallinity.

Highly Flexible Poly(1,12-dodecylene 5,5'-isopropylidene-bis(ethyl 2-furoate)): A Promising Biobased Polyester Derived from a Renewable Cost-Effective Bisfuranic Precursor and a Long-Chain Aliphatic Spacer

The continuous search for novel biobased polymers with high-performance properties has highlighted the role of monofuranic-based polyesters as some of the most promising for future plastic industry but has neglected the huge potential for the polymers' innovation, relatively low cost, and synthesis easiness of 5,5'-isopropylidene bis-(ethyl 2-furoate) (DEbF), obtained from the platform chemical, worldwide-produced furfural. In this vein, poly(1,12-dodecylene 5,5'-isopropylidene -bis(ethyl 2-furoate)) (PDDbF) was introduced, for the first time, as a biobased bisfuranic long-chain aliphatic polyester with an extreme flexibility function, competing with fossil-based polyethylene. This new polyester in-depth characterization confirmed its expected structure (FTIR, ¹H, and ¹³C NMR) and relevant thermal features (DSC, TGA, and DMTA), notably, an essentially amorphous character with a glass transition temperature of -6 °C and main maximum decomposition temperature of 340 °C. Furthermore, PDDbF displayed an elongation at break as high as 732%, around five times higher than that of the 2,5-furandicarboxylic acid counterpart, stressing the unique features of the bisfuranic class of polymers compared to monofuranic ones. The enhanced ductility combined with the relevant thermal properties makes PDDbF a highly promising material for flexible packaging.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Improving the Wet-Spinning and Drawing Processes of Poly(lactide)/Poly(ethylene furanoate) and Polylactide/Poly(dodecamethylene furanoate) Fiber Blends

This work aims to produce poly(lactic acid) (PLA)/poly(alkylene furanoate)s (PAF)s fiber blends for textile applications and evaluates their microstructural, chemical, thermal, and mechanical properties. The work focuses on two PAFs with very different alkyl chain lengths, i.e., poly(ethylene 2,5−furandicarboxylate) (PEF) and poly(dodecamethylene 2,5−furandicarboxylate) (PDoF), which were blended in solution at various concentrations (in the range 2.5–10 wt %) with PLA, wet spun, and subsequently drawn. Light optical micrographs highlight that PLA/PEF blends present large and concentrate PEF domains, whereas PLA/PDoF blends show small and homogeneously distributed PDoF domains. The blends appear to be immiscible, which is confirmed also by scanning electron microscopy (SEM), Fourier−Transform Infrared (FT−IR) spectroscopy, and differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) highlights that the addition of the PAFs improves the thermal stability of the fibers. The drawing process, which was carried out at 80 °C with a heat setting step at 95 °C and at three draw ratios, improves the mechanical properties of the fibers upon the addition of the PAFs. The results obtained in this study are promising and may serve as a basis for future investigations on these novel bio−based fiber blends, which can contribute to increase the environmental sustainability of industrial textiles.

Recent Progress on Bio-Based Polyesters Derived from 2,5-Furandicarbonxylic Acid (FDCA)

The big challenge today is the upgrading of sustainable materials to replace miscellaneous ones from petroleum resources. Thus, a generic bio-based building block lays the foundation of the huge bio-market to green economy. 2,5-Furandicarboxylic acid (FDCA), a rigid diacid derived from lignocellulose or fructose, represents a great potential as a contender to terephthalic acid (TPA). Recently, studies on the synthesis, modification, and functionalization of bio-based polyesters based on FDCA have attracted widespread attention. To apply furanic polyesters on engineering plastics, packaging materials, electronics, etc., researchers have extended the properties of basic FDCA-based homo-polyesters by directional copolymerization and composite preparation. This review covers the synthesis and performance of polyesters and composites based on FDCA with emphasis bedded on the thermomechanical, crystallization, barrier properties, and biodegradability. Finally, a summary of what has been achieved and the issues waiting to be addressed of FDCA-based polyester materials are suggested.

Poly(butylene 2,4-furanoate), an Added Member to the Class of Smart Furan-Based Polyesters for Sustainable Packaging: Structural Isomerism as a Key to Tune the Final Properties

High-molecular-weight poly(butylene 2,4-furanoate) (2,4-PBF), an isomer of well-known poly(butylene 2,5-furanoate) (2,5-PBF), was synthesized through an eco-friendly solvent-free polycondensation process and processed in the form of an amorphous film by compression molding. Molecular characterization was carried out by NMR spectroscopy and GPC analysis, confirming the chemical structure and high polymerization degree. Thermal analyses evidenced a reduction of both glass-to-rubber transition and melting temperatures, as well as a detriment of crystallization capability, for 2,4-PBF with respect to 2,5-PBF. Nevertheless, it was possible to induce crystal phase formation by annealing treatment. Wide-angle X-ray scattering revealed that the crystal lattices developed in the two isomers are distinct from each other. The different isomerism affects also the thermal stability, being 2,4-PBF more thermally inert than 2,5-PBF. Functional properties, such as wettability, mechanical response, and gas barrier capability, were tested on both amorphous and semicrystalline 2,4-PBF films and compared with those of 2,5-PBF. Reduced hydrophilicity was determined for 2,4-isomer, in line with its lower average dipole moment, suggesting better chemical resistance to hydrolysis. Stress-strain tests have evidenced the higher flexibility and toughness of 2,4-PBF with respect to those of 2,5-PBF and the possibility of improving its mechanical resistance by annealing. Finally, the different isomerism deeply affects the gas barrier performance, being the O₂- and CO₂-transmission rates of 2,4-PBF 50 and 110 times lower, respectively, than those of 2,5-PBF. The gas barrier properties turned out to be outstanding under a dry atmosphere as well as in humid conditions, suggesting the presence of interchain hydrogen bonds. The gas blocking capability decreases after annealing because of the presence of disclination associated with the formation of crystals.

Achievements and Trends in Biocatalytic Synthesis of Specialty Polymers from Biomass-Derived Monomers Using Lipases

New technologies for the conversion of biomass into high-value chemicals, including polymers and plastics, is a must and a challenge. The development of green processes in the last decade involved a continuous increase of the interest towards the synthesis of polymers using in vitro biocatalysis. Among the remarkable diversity of new bio-based polymeric products meeting the criteria of sustainability, biocompatibility, and eco-friendliness, a wide range of polyesters with shorter chain length were obtained and characterized, targeting biomedical and cosmetic applications. In this review, selected examples of such specialty polymers are presented, highlighting the recent developments concerning the use of lipases, mostly in immobilized form, for the green synthesis of ε-caprolactone co-polymers, polyesters with itaconate or furan units, estolides, and polyesteramides. The significant process parameters influencing the average molecular weights and other characteristics are discussed, revealing the advantages and limitations of biocatalytic processes for the synthesis of these bio-based polymers.

Biotechnological production and high potential of furan-based renewable monomers and polymers

Of the 25 million tons of plastic waste produced every year in Europe, 40% of these are not reused or recycled, thus contributing to environmental pollution, one of the major challenges of the 21st century. Most of these plastics are made of petrochemical-derived polymers which are very difficult to degrade and as a result, a lot of research efforts have been made on more environmentally friendly alternatives. Bio-based monomers, derived from renewable raw materials, constitute a possible solution for the replacement of oil-derived monomers, with furan derivatives that emerged as platform molecules having a great potential for the synthesis of biobased polyesters, polyamides and their copolymers. This review article summarizes the latest developments in biotechnological production of furan compounds that can be used in polymer chemistry as well as in their conversion into polymers. Moreover, the biodegradability of the resulting materials is discussed.

Unlocking the potential of furan-based poly(ester amide)s: an investigation of crystallization, molecular dynamics and degradation kinetics of novel poly(ester amide)s based on renewable poly(propylene furanoate)

In this work, novel polyester amides (PEAs) based on renewable poly(propylene furanoate) (PPF) were prepared via traditional melt polycondensation utilizing a preformed symmetric amido diol (AD) containing two internal amide bonds.

Tuning the Properties of Furandicarboxylic Acid-Based Polyesters with Copolymerization: A Review

Polyesters based on 2,5-furandicarboxylic acid (FDCA) are a new class of biobased polymers with enormous interest, both from a scientific and industrial perspective. The commercialization of these polymers is imminent as the pressure for a sustainable economy grows, and extensive worldwide research currently takes place on developing cost-competitive, renewable plastics. The most prevalent method for imparting these polymers with new properties is copolymerization, as many studies have been published over the last few years. This present review aims to summarize the trends in the synthesis of FDCA-based copolymers and to investigate the effectiveness of this approach in transforming them to a more versatile class of materials that could potentially be appropriate for a number of high-end and conventional applications.

Ultraflexible Transparent Bio-Based Polymer Conductive Films Based on Ag Nanowires

The unstable mechanical properties of flexible transparent conductive films (TCFs) make it difficult for them to meet the requirements for displays or wearable devices. Here, the relationship between the mechanism behind the bending behavior and the electrical properties, which is important for improving the mechanical stability of flexible TCFs, is explored. Flexible TCFs are reported based on silver nanowires (AgNWs) and bio-based poly(ethylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate)s (PECFs), with a low sheet resistance (23.8 Ω sq^-1 at 84.6% transmittance) and superior mechanical properties. The electrical properties of the AgNW/PECFs composite film show almost no change after bending for 2000 times.

Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, III: Extended Study on Effect of Catalyst Type on Molecular Weight Increase

In this study, the synthesis of poly(ethylene furanoate) (PEF), catalyzed by five different catalysts-antimony acetate (III) (Sb Ac), zirconium (IV) isopropoxide isopropanal (Zr Is Ip), antimony (III) oxide (Sb Ox), zirconium (IV) 2,4-pentanedionate (Zr Pe) and germanium (IV) oxide (Ge Ox)-via an industrially common combination of melt polymerization and subsequent solid-state polymerization (SSP) is presented. In all reactions, proper amounts of 2,5-dimethylfuran-dicarboxylate (DMFD) and ethylene glycol (EG) in a molar ratio of DMFD/EG= 1/2 and 400 ppm of catalyst were used. Polyester samples were subjected to SSP procedure, under vacuum application, at different reaction times (1, 2, 3.5, and 5 h) and temperatures of 190, 200, and 205 °C. Carboxyl end-groups concentration (⁻COOH), intrinsic viscosity (IV), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polymers to study the effect of the used catalysts on the molecular weight increase of PEF during SSP process. As was expected, it was found that with increasing the SSP time and temperature, the intrinsic viscosity and the average molecular weight of PEF steadily increased. In contrast, the number of carboxyl end-groups content showed the opposite trend as intrinsic viscosity, that is, gradually decreasing during SSP time and temperature increase. It is worthy to note that thanks to the SSP process an obvious and continuous enhancement in the thermal properties of the prepared PEF samples was attained, in which their melting temperatures (Tm) and degree of crystallinity (Xc) increase progressively with increasing of reaction time and temperature. To predict the time evolution of polymers IV, as well as the hydroxyl and carboxyl content of PEF polyesters during the SSP, a simple kinetic model was developed. From both the theoretical simulation results and the experimental measurements, it was demonstrated that surely the Zr Is Ip catalyst shows the best catalytic characteristics compared to all other used catalysts herein, that is, leading in reducing-in a spectacular way-the activation energy of the involved both transesterification and esterification reactions during SSP.

Modification of Poly(ethylene 2,5-furandicarboxylate) with Biobased 1,5-Pentanediol: Significantly Toughened Copolyesters Retaining High Tensile Strength and O2 Barrier Property

Poly(ethylene 2,5-furandicarboxylate) (PEF) is a biobased polyester characterized by high gas barrier properties as well as high tensile modulus and strength, but poor toughness. Toughening PEF without sacrificing its modulus, strength and gas barrier performance is a great challenge for PEF modification. In this study, high molecular weight random poly(ethylene- co-1,5-pentylene 2,5-furandicarboxylate)s (PEPeFs) were synthesized via melt copolycondensation of 2,5-furandicarboxylic acid (FDCA), ethylene glycol (EG) and 1,5-pentanediol (PeDO), a cheap, biobased and commercially available odd-carbon comonomer. The synthesized PEPeFs were characterized and assessed with intrinsic viscosity, ATR-FTIR, ¹H NMR, DSC, TGA and tensile, impact and O₂ permeation test. Mayo-Lewis equation with "reactivity ratio" of 3.78 for PeDO and 0.75 for EG could be used as an empirical equation to correlate the copolyester composition (ϕ_PeF) with monomer composition. PEPeFs proved nearly amorphous copolyesters having excellent thermal stability. Brittle-ductile transition was achieved at ϕ_PeF as low as 9 mol %. Increasing ϕ_PeF led to increase in elongation at break and notch impact strength and decrease in T_g, O₂ barrier performance and tensile modulus and strength. However, in comparison with PEF, PEF-rich PEPeFs (ϕ_PeF 9-47%) not only showed greatly improved elongation at break (29-265% vs 4%) and enhanced impact strength (2.2-3.9 kJ/m²) but also retained very high Young's modulus (2.8-3.3 vs 3.3 GPa) and yielding strength (72-83 vs 82 MPa). Particularly, when compared with bottle-grade PET, PE₈₂Pe₁₈F possesses equal T_g (ca. 75 °C) and comparable elongation at break (ca. 115%), but greatly improved yielding strength (83 MPa) and O₂ gas barrier property (4.8 times). As modified PEF materials possessing superior thermo-mechanical and O₂ gas barrier properties, these integrally biobased copolyesters may find practical applications in eco-packaging and other fields.

UV-Blocking Synthetic Biopolymer from Biomass-Based Bifuran Diester and Ethylene Glycol

A furan-based synthetic biopolymer composed of a bifuran monomer and ethylene glycol was synthesized through melt polycondensation, and the resulting polyester was found to have promising thermal and mechanical properties. The bifuran monomer, dimethyl 2,2′-bifuran-5,5′-dicarboxylate, was prepared using a palladium-catalyzed, phosphine ligand-free direct coupling protocol. A titanium-catalyzed polycondensation procedure was found effective at polymerizing the bifuran monomer with ethylene glycol. The prepared bifuran polyester exhibited several intriguing properties including high tensile modulus. In addition, the bifuran monomer furnished the polyester with a relatively high glass transition temperature. Films prepared from the new polyester also had excellent oxygen and water barrier properties, which were found to be superior to those of poly(ethylene terephthalate). Moreover, the novel polyester also has good ultraviolet radiation blocking properties.

Poly(butylene 2,5-thiophenedicarboxylate): An Added Value to the Class of High Gas Barrier Biopolyesters

Many efforts are currently devoted to the design and development of high performance bioplastics to replace traditional fossil-based polymers. In response, this contribution presents a new biobased aromatic polyester, i.e., poly(butylene 2,5-thiophenedicarboxylate) (PBTF). Here, PBTF is characterized from the molecular, thermo-mechanical and structural point of view. Gas permeability is evaluated at different temperatures, in the range below and above glass transition, providing a full insight into the performances of this material under different operating conditions, and demonstrating the superior gas barrier behavior of PBTF with respect to other polyesters, such as PEF and PET. The combination of calorimetric and diffractometric studies allows for a deep understanding of the structure of PBTF, revealing the presence of a not-induced 2D-ordered phase (meso-phase), responsible for its outstanding gas permeability behavior. The simple synthetic strategy adopted, the exceptional barrier properties, combined with the interesting mechanical characteristics of PBTF open up new scenarios in the world of green and sustainable packaging materials.

Solid-State Polymerization of Poly(ethylene furanoate) Biobased Polyester, I: Effect of Catalyst Type on Molecular Weight Increase

In this work, we report the synthesis of poly(ethylene furanoate) (PEF), catalyzed by three different catalysts, namely, titanium (IV) isopropoxide (TIS), tetrabutyltitanate (TBT), and dibutyltin (IV) oxide (DBTO), via the two-stage melt polycondensation method. Solid-state polymerization (SSP) was conducted at different reaction times (1, 2, 3.5, and 5 h) and temperatures 190, 200, and 205 °C, under vacuum. The resultant polymers were analyzed according to their intrinsic viscosity (IV), end groups (⁻COOH), and thermal properties, via differential scanning calorimetry. DSC results showed that the post polymerization process was favorable to enhance the melting point of the prepared PEF samples. As was expected, the intrinsic viscosity and the average molecular weight of PEF increased with the SSP time and temperature, whereas the number of carboxyl end-groups was decreased. A simple kinetic model was also developed and used to predict the time evolution of polymers IV, as well as the carboxyl and hydroxyl content of PEF during the SSP. From both the experimental measurements and the theoretical simulation results it was proved that the presence of the TIS catalyst resulted in higher transesterification kinetic rate constants and higher reaction rates. The activation energies were not much affected by the presence of different catalysts. Finally, using DBTO as a catalyst, the polyesters produced have higher crystallinity, and as a consequence, higher number of inactive carboxyl and hydroxyl groups.