Biocatalyst immobilization on magnetic nano-architectures for potential applications in condensation reactions

In this review article, a perspective on the immobilization of various hydrolytic enzymes onto magnetic nanoparticles for synthetic organic chemistry applications is presented. After a first part giving short overview on nanomagnetism and highlighting advantages and disadvantages of immobilizing enzymes on magnetic nanoparticles (MNPs), the most important hydrolytic enzymes and their applications were summarized. A section reviewing the immobilization techniques with a particular focus on supporting enzymes on MNPs introduces the reader to the final chapter describing synthetic organic chemistry applications of small molecules (flavour esters) and polymers (polyesters and polyamides). Finally, the conclusion and perspective section gives the author's personal view on further research discussing the new idea of a synergistic rational design of the magnetic and biocatalytic component to produce novel magnetic nano-architectures.

Enzymatic Synthesis of Copolyesters with the Heteroaromatic Diol 3,4-Bis(hydroxymethyl)furan and Isomeric Dimethyl Furandicarboxylate Substitutions

Polyesters from furandicarboxylic acid derivatives, i.e., dimethyl 2,5-furandicarboxylate (2,5-DMFDCA) and 2,4-DMFDCA, show interesting properties among bio-based polymers. Another potential heteroaromatic monomer, 3,4-bis(hydroxymethyl)furan (3,4-BHMF), is often overlooked but holds promise for biopolymer synthesis. Cleaning and greening synthetic procedures, i.e., enzymatic polymerization, offer sustainable pathways. This study explores the Candida antarctica lipase B (CALB)-catalyzed copolymerization of 3,4-BHMF with furan dicarboxylate isomers and aliphatic diols. The furanic copolyesters (co-FPEs) with higher polymerization degrees are obtained using 2,4-isomer, indicating CALB's preference. Material analysis revealed semicrystalline properties in all synthesized 2,5-FDCA-based co-FPEs, with multiple melting temperatures (Tm) from 53 to 124 °C and a glass-transition temperature (Tg) of 9-10 °C. 2,4-FDCA-based co-FPEs showed multiple Tm from 43 to 61 °C and Tg of -14 to 12 °C; one of them was amorphous. In addition, all co-FPEs showed a two-step decomposition profile, indicating aliphatic and semiaromatic segments in the polymer chains.

Wound healing potential of silver nanoparticles embedded in optimized bio-inspired hybridized chitosan soft and dry hydrogel

Interactive wound dressings combining healing and antimicrobial potentials, besides ensuring patient compliance with a recognized wound care service gained considerable interest recently. Both hydrogel spray dried microparticles (HMP) and soft hydrogel (G) were prepared. The bio-inspired combinatory platform included natural bio-macromolecules namely: chitosan (CS) and collagen (COL) with wound healing enhancement and connective tissue building capabilities cross linked with the natural genipin (GN) to build a three dimensional structured matrix. The optimized plain hydrogel obtained by a box behnken design (BBD) program (G) scored maximum swelling and porosity. The network was hosted with green synthesized cefotaxime sodium (cef.Na) AgNPs reduced by the anabolic folic acid (FA). Both hydrogels exhibited good antimicrobial activity against gram +ve and -ve bacteria. The wound healing activity, evaluated in injured rats, showed >98 % and complete wound closure after two and three weeks respectively. Oxidative stress minimization was proved by the estimation of biochemical markers malondialdehyde (MDA) and superoxide dismutase (SOD) levels at the wound site.

Enzymatically catalyzed furan-based copolyesters containing dilinoleic diol as a building block

A more environmentally friendly method for creating sustainable alternatives to traditional aromatic-aliphatic polyesters is a valuable step towards resource-efficiency optimization. A library of furan-based block copolymers was synthesized via temperature-varied two-step polycondensation reaction in diphenyl ether using Candida antarctica lipase B (CAL-B) as a biocatalyst where dimethyl 2,5-furandicarboxylate (DMFDCA), α,ω-aliphatic linear diols (α,ω-ALD), and bio-based dilinoleic diol (DLD) were used as the starting materials. Nuclear magnetic spectroscopy (¹H and ¹³C NMR), Fourier transform spectroscopy (FTIR) and size exclusion chromatography (SEC) were used to analyze the resulting copolymers. Additionally, crystallization behavior and thermal properties were studied using X-ray diffraction (XRD), digital holographic microscopy (DHM), and differential scanning microscopy (DSC). Finally, oxygen transmission rates (OTR) and dynamic mechanical analysis (DMTA) of furan-based copolyesters indicated their potential for medical packaging.

Toughening Effect of 2,5-Furandicaboxylate Polyesters on Polylactide-Based Renewable Fibers

This work presents the successful preparation and characterization of polylactide/poly(propylene 2,5-furandicarboxylate) (PLA/PPF) and polylactide/poly(butylene 2,5-furandicarboxylate) (PLA/PBF) blends in form of bulk and fiber samples and investigates the influence of poly(alkylene furanoate) (PAF) concentration (0 to 20 wt%) and compatibilization on the physical, thermal, and mechanical properties. Both blend types, although immiscible, are successfully compatibilized by Joncryl (J), which improves the interfacial adhesion and reduces the size of PPF and PBF domains. Mechanical tests on bulk samples show that only PBF is able to effectively toughen PLA, as PLA/PBF blends with 5-10 wt% PBF showed a distinct yield point, remarkable necking propagation, and increased strain at break (up to 55%), while PPF did not show significant plasticizing effects. The toughening ability of PBF is attributed to its lower glass transition temperature and greater toughness than PPF. For fiber samples, increasing the PPF and PBF amount improves the elastic modulus and mechanical strength, particularly for PBF-containing fibers collected at higher take-up speeds. Remarkably, in fiber samples, plasticizing effects are observed for both PPF and PBF, with significantly higher strain at break values compared to neat PLA (up to 455%), likely due to a further microstructural homogenization, enhanced compatibility, and load transfer between PLA and PAF phases following the fiber spinning process. SEM analysis confirms the deformation of PPF domains, which is probably due to a "plastic-rubber" transition during tensile testing. The orientation and possible crystallization of PPF and PBF domains contribute to increased tensile strength and elastic modulus. This work showcases the potential of PPF and PBF in tailoring the thermo-mechanical properties of PLA in both bulk and fiber forms, expanding their applications in the packaging and textile industry.

Hytrel-like Copolymers Based on Furan Polyester: The Effect of Poly(Butylene Furanoate) Segment on Microstructure and Mechanical/Elastic Performance

This paper aims to compare the performance of two Hytrel-like segmented copolymers: “classic” PBT-b-PTMG and fully bio-based PBF-b-PTMG, containing poly(butylene furanoate) as the rigid segment. The idea behind this research is to assess whether the sustainable copolymers can successfully replace those “classic” once at the thermoplastic elastomers’ market. Two series of copolymers were synthesized under the same process parameters, had the same compositions, but differed in aromatic ring structure in terephthalate/furanoate unit. Furthermore, the materials were processed by injection moulding as typical Hytrel products. Then, the samples were subjected to extensive characterisation including NMR, GPC, FTIR, DSC, WAXS, DMTA, TGA techniques and mechanical tests with particular interest in the microstructure formed during processing and its effect on the copolymers’ mechanical and elastic behaviour. The detailed analysis proved that PBF-b-PTMG and PBT-b-PTMG copolymers represent two kinds of materials with similar chemical structure, some features of thermoplastic elastomers, but evident differences in their physical properties.

Biobased 2,5-Bis(hydroxymethyl)furan as a Versatile Building Block for Sustainable Polymeric Materials

Furanic polymers, currently mainly represented by polyethylene 2,5-furandicarboxylate (PEF), also known as polyethylene furanoate, have a fantastic potential to replace fossil-based polymers: for example, polyethylene terephthalate (PET). While 2,5-furandicarboxylic acid (FDCA), a precursor of PEF, and its derived polymers have been studied extensively, 2,5-bis(hydroxymethyl)furan (BHMF) has received relatively little attention so far. Similarly to FDCA, BHMF is a biobased platform chemical derived from renewable sources such as sugars. This review highlights different polymerization techniques for BHMF-based polyesters and addresses BHMF's relative instability during the synthesis of BHMF-derived polymers, including polycarbonates and polyurethanes. Furthermore, the degradability of furanic polyesters is discussed and BHMF's toxicity is briefly elaborated.

Supramolecular structure, relaxation behavior and free volume of bio-based poly(butylene 2,5-furandicarboxylate)-block-poly(caprolactone) copolyesters

In the present study, a fully plant-based sustainable copolyester series, namely poly(butylene 2,5-furandicarboxylate)-block-poly(caprolactone)s (PBF-block-PCL)s were successfully synthesized by melt polycondensation combining butylene 2,5-furandicarboxylate with polycaprolactone diol (PCL) at different weight ratios. Differential scanning calorimetry (DSC) showed that only PBF underwent melting, crystallization from the melt, and cold crystallization. Thermogravimetric analysis (TGA) revealed outstanding thermal stability, exceeding 305 °C, with further improvement in thermal and thermo-oxidative stability with increasing PCL content. Broadband dielectric spectroscopy (BDS) revealed that at low temperatures, below the glass transition (T_g) all copolyesters exhibited two relaxation processes (β₁ and β₂), whereas the homopolymer PBF exhibited a single β-relaxation, which is associated with local dynamics of the different chemical bonds present in the polymer chain. Additionally, it was proved that an increase in PCL content affected the dynamics of the chain making it more flexible, thus providing an increase in the value of the room temperature free volume fractions (f_v) and the value of elongation at break. These effects are accompanied by a decrease in hardness, Young's modulus, and tensile strength. The described synthesis enables a facile approach to obtain novel fully multiblock biobased copolyesters based on PBF and PCL polyesters with potential industrial implementation capabilities.

Enzyme catalyzes ester bond synthesis and hydrolysis: The key step for sustainable usage of plastics

Petro-plastic wastes cause serious environmental contamination that require effective solutions. Developing alternatives to petro-plastics and exploring feasible degrading methods are two solving routes. Bio-plastics like polyhydroxyalkanoates (PHAs), polylactic acid (PLA), polycaprolactone (PCL), poly (butylene succinate) (PBS), poly (ethylene furanoate) s (PEFs) and poly (ethylene succinate) (PES) have emerged as promising alternatives. Meanwhile, biodegradation plays important roles in recycling plastics (e.g., bio-plastics PHAs, PLA, PCL, PBS, PEFs and PES) and petro-plastics poly (ethylene terephthalate) (PET) and plasticizers in plastics (e.g., phthalate esters, PAEs). All these bio- and petro-materials show structure similarity by connecting monomers through ester bond. Thus, this review focused on bio-plastics and summarized the sequences and structures of the microbial enzymes catalyzing ester-bond synthesis. Most of these synthetic enzymes belonged to α/β-hydrolases with conserved serine catalytic active site and catalyzed the polymerization of monomers by forming ester bond. For enzymatic plastic degradation, enzymes about PHAs, PBS, PCL, PEFs, PES and PET were discussed, and most of the enzymes also belonged to the α/β hydrolases with a catalytic active residue serine, and nucleophilically attacked the ester bond of substrate to generate the cleavage of plastic backbone. Enzymes hydrolysis of the representative plasticizer PAEs were divided into three types (I, II, and III). Type I enzymes hydrolyzed only one ester-bond of PAEs, type II enzymes catalyzed the ester-bond of mono-ester phthalates, and type III enzymes hydrolyzed di-ester bonds of PAEs. Divergences of catalytic mechanisms among these enzymes were still unclear. This review provided references for producing bio-plastics, and degrading or recycling of bio- and petro-plastics from an enzymatic point of view.

Enzymatic synthesis of novel aromatic-aliphatic polyesters with increased hydroxyl group density

BACKGROUND

Polyesters with pendant hydroxyl groups are attractive materials which offer additional functionalization points in the polymer chain. In contrast to chemical polycondensation, lipase regioselectivity enables the synthesis of these materials as certain hydroxyl groups remain unaffected during the enzymatic process.

METHODS AND MAJOR RESULTS

In this study, a combination of synthesis development and reactor design was used for the enzymatic synthesis of an aliphatic-aromatic polyester with two different classes of pendant hydroxyl groups. Using 2,6-bishydroxy(methyl)-p-cresol as diol in lipase catalyzed polycondensation with adipic acid required the addition of hexane diol as third monomer for polycondensation to take place. Reaction conditions were explored in order to identify the preferred reaction conditions for the incorporation of the aromatic diol and the enhancement of the hydroxyl group density. Post-polymerization with glycerol at low temperature integrated additional aliphatic hydroxyl groups, reduced the polydispersity and increased the end group functionality.

CONCLUSION

A new material with aromatic building blocks and boosted polymer chain reactivity was obtained, which is suggested to find application in various areas of material development from coatings to adhesives. This article is protected by copyright. All rights reserved.

Bio-based and one-day compostable poly(diethylene 2,5-furanoate) for sustainable flexible food packaging: Effect of ether-oxygen atom insertion on the final properties

In the present work, the effect of ether oxygen atom introduction in a furan ring-containing polymer has been evaluated. Solvent-free polycondensation process permitted the preparation of high molecular weight poly(diethylene 2,5-furandicarboxylate) (PDEF), by reacting the dimethyl ester of 2,5-furandicarboxylic acid with diethylene glycol. After molecular and thermal characterization, PDEF mechanical response and gas barrier properties to O₂ and CO₂, measured at different temperatures and humidity, were studied and compared with those of poly(butylene 2,5-furandicarboxylate) (PBF) and poly(pentamethylene 2,5-furanoate) (PPeF) previously determined. Both PDEF and PPeF films were amorphous, differently from PBF one. Glass transition temperature of PDEF (24 °C) is between those of PBF (39 °C) and PPeF (13 °C). As concerns mechanical response, PDEF is more flexible (elastic modulus [E] = 673 MPa) than PBF (E = 1290 MPa) but stiffer than PPeF (E = 9 MPa). Moreover, PDEF is the most thermally stable (temperature of maximum degradation rate being 418 for PDEF, 407 for PBF and 414 °C for PPeF) and hydrophilic (water contact angle being 74° for PDEF, 90° for PBF and 93° for PPeF), with gas barrier performances very similar to those of PPeF (O₂ and CO₂ transmission rate being 0.0022 and 0.0018 for PDEF and, 0.0016 and 0.0014 cm³ cm/m² d atm for PPeF). Lab scale composting experiments indicated that PDEF and PPeF were compostable, the former degrading faster, in just one day. The results obtained are explained on the basis of the high electronegativity of ether oxygen atom with respect to the carbon one, and the consequent increase of dipoles along the macromolecule.

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.

Effects of Nonhydroxyl Oxygen Heteroatoms in Diethylene Glycols on the Properties of 2,5-Furandicarboxylic Acid-Based Polyesters

With regard to polyesters based on biobased 2,5-furandicarboxylic acid (FDCA), our work presents a new strategy, heteroatom substitution, to adjust the thermal and gas barrier properties. The effects of nonhydroxyl oxygen heteroatoms in the diols on the properties of FDCA-based polyesters were first investigated by a combination of an experiment and molecular simulation. The results demonstrated that the introduction of oxygen heteroatoms significantly influenced the thermal and gas barrier properties. As for the two model polymers with a very similar skeleton structure, poly(pentylene 2,5-furandicarboxylate) (PPeF) and poly(diethylene glycol 2,5-furandicarboxylate) (PDEF), their T_g exhibited an obviously increasing order. Moreover, they showed similar thermal stability and thermal oxidative stability. Dynamic mechanical analysis, positron annihilation lifetime spectroscopy, and molecular dynamics simulation indicated that the gas barrier properties followed the sequence of PDEF > PPeF mainly due to the decreased chain mobility and smaller fractional free volume. In-depth analysis of the effects of heteroatom substitution has an important directive significance for the design and preparation of new high glass transition temperature or novel excellent gas barrier materials. Through the manipulation of different heteroatoms in the diols, the polyesters with varied properties can be expected.

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.

Polymer Chemistry Applications of Cyrene and its Derivative Cygnet 0.0 as Safer Replacements for Polar Aprotic Solvents

This study explores a binary solvent system composed of biobased Cyrene and its derivative Cygnet 0.0 for application in membrane technology and in biocatalytic synthesis of polyesters. Cygnet-Cyrene blends could represent viable replacements for toxic polar aprotic solvents. The use of a 50 wt % Cygnet-Cyrene mixture makes a practical difference in the production of flat sheet membranes by nonsolvent-induced phase separation. New polymeric membranes from cellulose acetate, polysulfone, and polyimide are manufactured by using Cyrene, Cygnet 0.0, and their blend. The resultant membranes have different morphology when the solvent/mixture and temperature of the casting solution change. Moreover, Cyrene, Cygnet 0.0, and Cygnet-Cyrene are also explored for substituting diphenyl ether for the biocatalytic synthesis of polyesters. The results indicate that Cygnet 0.0 is a very promising candidate for the enzymatic synthesis of high molecular weight polyesters.

Enzymatic Synthesis of Polyesters and Their Bioapplications: Recent Advances and Perspectives

This article reviews the most important advances in the enzymatic synthesis of polyesters. In first place, the different processes of polyester enzymatic synthesis, i.e., polycondensation, ring opening, and chemoenzymatic polymerizations, and the key parameters affecting these reactions, such as enzyme, concentration, solvent, or temperature, are analyzed. Then, the latest articles on the preparation of polyesters either by direct synthesis or via modification are commented. Finally, the main bioapplications of enzymatically obtained polyesters, i.e., antimicrobial, drug delivery, or tissue engineering, are described. It is intended to point out the great advantages that enzymatic polymerization present to obtain polymers and the disadvantages found to develop applied materials.

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.

Mechanical and Functional Properties of Novel Biobased Poly(decylene-2,5-furanoate)/Carbon Nanotubes Nanocomposite Films

The present work investigates the microstructural, thermo-mechanical, and electrical properties of a promising, but still not thoroughly studied, biobased polymer, i.e., poly(decylene furanoate) (PDeF), and its performance when multi-walled carbon nanotubes (CNTs) are added. After sample preparation by solution mixing and film casting, the microstructural investigation evidences that the fracture surface becomes smoother and more homogeneous with a small fraction of CNTs, and that the production process is suitable to achieve good disentanglement and dispersion of CNTs within the matrix, although some aggregates are still observable. CNTs act as nucleating agents for PDeF crystals, as evidenced by differential scanning calorimetry, as the crystallinity degree increases from 43.2% of neat PDeF to 55.0% with a CNT content of 2 phr, while the crystallization temperature increases from 68.4 °C of PDeF to 91.7 °C of PDeF-CNT-2. A similar trend in crystallinity is confirmed by X-ray diffraction, after detailed Rietveld analysis with a three-phase model. CNTs also remarkably improve the mechanical performance of the bioderived polymer, as the elastic modulus increases up to 123% and the stress at break up to 131%. The strain at break also increases by +71% when a small amount of 0.25 phr of CNTs are added, which is probably the consequence of a more homogeneous microstructure. The long-term mechanical performance is also improved upon CNT addition, as the creep compliance decreases considerably, which was observed for both the elastic and the viscoelastic component. Finally, the films become electrically dissipative for a CNT content of 1 phr and conductive for a CNT amount of 2 phr. This study contributes to highlight the properties of bioderived furan-based polymer PDeF and evidences the potential of CNTs as a promising nanofiller for this matrix.

Renewable polymers and plastics: Performance beyond the green

Renewable bio-based polymers are one of the effective answers that the bioeconomy offers to solve the environmental emergency connected to plastics and more specifically fossil-based plastics. Previous studies have shown that more than 70 % of the natural capital cost associated with plastic derives from the extraction and processing of fossil raw materials and that the price of fossil plastic would be on average 44 % higher if such impact was fully paid by businesses. The disclosure of the hidden costs of plastics will contribute to dispelling the myth of the expensiveness of renewable polymers. Nevertheless, the adoption of bio-based plastics in the market must be motivated by their functional properties and not merely by their green credentials. This article highlights some successful examples of synergies between chemistry and biotechnology in achieving a new generation of bio-based monomers and polymers. Their success is justified by the combination of scientific advances with positive environmental and social fallouts.

Recent advances in the synthesis of biodegradable polyesters by sustainable polymerization: lipase-catalyzed polymerization

Over the past three decades, enzymatic polymerization has dramatically developed and gradually broadened as a creative methodology in the construction of polymeric materials with tailor-made structures and properties. Compared with transition metal catalyst polymerizations, enzymatic polymerization is more attractive in the biomedicine field due to the metal-free residue, good biocompatibility, and few by-products. Meanwhile, enzymatic polymerization has far more activity towards macrolides. In this review, the synthesis of lipase-catalyzed polymer materials is systematically summarized, focusing on the synthesis of the complex and well-defined polymers. The enzymatic polyester synthesis was then discussed concerning the different reaction types, including ring-opening polymerization, polycondensation, a combination of ring-opening polymerization with polycondensation, and chemoenzymatic polymerization. Besides, exploration of novel biocatalysts and reaction media was also described, with particular emphasis on the enzymes obtained via immobilization or protein engineering strategies, green solvents, and reactors. Finally, recent developments in catalytic kinetics and mechanistic studies through the use of spectroscopy, mathematics, and computer techniques have been introduced. Besides, we addressed the remaining central issues in enzymatic polymerization and discussed current studies aimed at providing answers.

Enzymatic Polycondensation of 1,6-Hexanediol and Diethyl Adipate: A Statistical Approach Predicting the Key-Parameters in Solution and in Bulk

Among the various catalysts that can be used for polycondensation reactions, enzymes have been gaining interest for three decades, offering a green and eco-friendly platform towards the sustainable design of renewable polyesters. However, limitations imposed by their delicate nature, render them less addressed. As a case study, we compare herein bulk and solution polycondensation of 1,6-hexanediol and diethyl adipate catalyzed by an immobilized lipase from Candida antarctica. The influence of various parameters including time, temperature, enzyme loading, and vacuum was assessed in the frame of a two-step polymerization with the help of response surface methodology, a statistical technique that investigates relations between input and output variables. Results in solution (diphenyl ether) and bulk conditions showed that a two-hour reaction time was enough to allow adequate oligomer growth for the first step conducted under atmospheric pressure at 100 °C. The number-average molecular weight (M_n) achieved varied between 5000 and 12,000 g·mol^-1 after a 24 h reaction and up to 18,500 g∙mol^-1 after 48 h. The statistical analysis showed that vacuum was the most influential factor affecting the M_n in diphenyl ether. In sharp contrast, enzyme loading was found to be the most influential parameter in bulk conditions. Recyclability in bulk conditions showed a constant M_n of the polyester over three cycles, while a 17% decrease was noticed in solution. The following work finally introduced a statistical approach that can adequately predict the M_n of poly(hexylene adipate) based on the choice of parameter levels, providing a handy tool in the synthesis of polyesters where the control of molecular weight is of importance.

A Perspective on PEF Synthesis, Properties, and End-Life

This critical review considers the extensive research and development dedicated, in the last years, to a single polymer, the poly(ethylene 2,5-furandicarboxylate), usually simply referred to as PEF. PEF importance stems from the fact that it is based on renewable resources, typically prepared from C6 sugars present in biomass feedstocks, for its resemblance to the high-performance poly(ethylene terephthalate) (PET) and in terms of barrier properties even outperforming PET. For the first time synthesis, properties, and end-life targeting—a more sustainable PEF—are critically reviewed. The emphasis is placed on how synthetic roots to PEF evolved toward the development of greener processes based on ring open polymerization, enzymatic synthesis, or the use of ionic liquids; together with a broader perspective on PEF end-life, highlighting recycling and (bio)degradation solutions.

Heterogeneous Catalytic Conversion of Sugars Into 2,5-Furandicarboxylic Acid

Achieving the goal of living in a sustainable and greener society, will need the chemical industry to move away from petroleum-based refineries to bio-refineries. This aim can be achieved by using biomass as the feedstock to produce platform chemicals. A platform chemical, 2,5-furandicarboxylic acid (FDCA) has gained much attention in recent years because of its chemical attributes as it can be used to produce green polymers such polyethylene 2,5-furandicarboxylate (PEF) that is an alternative to polyethylene terephthalate (PET) produced from fossil fuel. Typically, 5-(hydroxymethyl)furfural (HMF), an intermediate product of the acid dehydration of sugars, can be used as a precursor for the production of FDCA, and this transformation reaction has been extensively studied using both homogeneous and heterogeneous catalysts in different reaction media such as basic, neutral, and acidic media. In addition to the use of catalysts, conversion of HMF to FDCA occurs in the presence of oxidants such as air, O2, H2O2, and t-BuOOH. Among them, O2 has been the preferred oxidant due to its low cost and availability. However, due to the low stability of HMF and high processing cost to convert HMF to FDCA, researchers are studying the direct conversion of carbohydrates and biomass using both a single- and multi-phase approach for FDCA production. As there are issues arising from FDCA purification, much attention is now being paid to produce FDCA derivatives such as 2, 5-furandicarboxylic acid dimethyl ester (FDCDM) to circumvent these problems. Despite these technical barriers, what is pivotal to achieve in a cost-effective manner high yields of FDCA and derivatives, is the design of highly efficient, stable, and selective multi-functional catalysts. In this review, we summarize in detail the advances in the reaction chemistry, catalysts, and operating conditions for FDCA production from sugars and carbohydrates.

Fully Biobased Superpolymers of 2,5-Furandicarboxylic Acid with Different Functional Properties: From Rigid to Flexible, High Performant Packaging Materials

In the present paper, four fully biobased homopolyesters of 2,5-furandicarboxylic acid (2,5-FDCA) with a high molecular weight have been successfully synthesized by two-stage melt polycondensation, starting from the dimethyl ester of 2,5-FDCA and glycols of different lengths (the number of methylene groups ranged from 3 to 6). The synthesized polyesters have been first subjected to an accurate molecular characterization by NMR and gel-permeation chromatography. Afterward, the samples have been successfully processed into free-standing thin films (thickness comprised between 150 to 180 μm) by compression molding. Such films have been characterized from the structural (by wide-angle X-ray scattering and small-angle X-ray scattering), thermal (by differential scanning calorimetry and thermogravimetric analysis), mechanical (by tensile test), and gas barrier (by permeability measurements) point of view. The glycol subunit length was revealed to be the key parameter in determining the kind and fraction of ordered phases developed by the sample during compression molding and subsequent cooling. After storage at room temperature for one month, only the homopolymers containing the glycol subunit with an even number of -CH2- groups (poly(butylene 2,5-furanoate) (PBF) and poly(hexamethylene 2,5-furanoate) (PHF)) were able to develop a three-dimensional ordered crystalline phase in addition to the amorphous one, the other two appearing completely amorphous (poly(propylene 2,5-furanoate (PPF) and poly(pentamethylene 2,5-furanoate) (PPeF)). From X-ray scattering experiments using synchrotron radiation, it was possible to evidence a third phase characterized by a lower degree of order (one- or two-dimensional), called a mesophase, in all the samples under study, its fraction being strictly related to the glycol subunit length: PPeF was found to be the sample with the highest fraction of mesophase followed by PHF. Such a mesophase, together with the amorphous and the eventually present crystalline phase, significantly impacted the mechanical and barrier properties, these last being particularly outstanding for PPeF, the polyester with the highest fraction of mesophase among those synthesized in the present work.

Broadband Dielectric Spectroscopy Study of Biobased Poly(alkylene 2,5-furanoate)s' Molecular Dynamics

Poly(2,5-alkylene furanoate)s are bio-based, smart, and innovative polymers that are considered the most promising materials to replace oil-based plastics. These polymers can be synthesized using ecofriendly approaches, starting from renewable sources, and result into final products with properties comparable and even better than those presented by their terephthalic counterparts. In this work, we present the molecular dynamics of four 100% bio-based poly(alkylene 2,5-furanoate)s, using broadband dielectric spectroscopy measurements that covered a wide temperature and frequency range. We unveiled complex local relaxations, characterized by the simultaneous presence of two components, which were dependent on thermal treatment. The segmental relaxation showed relaxation times and strengths depending on the glycolic subunit length, which were furthermore confirmed by high-frequency experiments in the molten region of the polymers. Our results allowed determining structure-property relations that are able to provide further understanding about the excellent barrier properties of poly(alkylene 2,5-furanoate)s. In addition, we provide results of high industrial interest during polymer processing for possible industrial applications of poly(alkylene furanoate)s.

Environmentally Friendly Polymer Blends Based on Post-Consumer Glycol-Modified Poly(Ethylene Terephthalate) (PET-G) Foils and Poly(Ethylene 2,5-Furanoate) (PEF): Preparation and Characterization

Environmentally friendly polymer blends between post-consumer PET-G and bio-based poly(ethylene 2,5 furanoate) (PEF) have been prepared. The PET-G granules were obtained from the post-consumer glycol-modified poly(ethylene terephthalate) PET-G foils from Nicrometal S.A. as a result of materials recycling. PEF was synthesized from dimethyl furan-2,5-dicarboxylate and 1,2-ethylene glycol (BioUltra) by a two-stage melt polycondensation process. According to the calculations followed by Hoy's method, one has studied the miscibility of the components in the blend. The molecular structure of PET-G/PEF blends was analyzed by Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, while the morphology of the blends was determined by Scanning Electron Microscopy (SEM). To evaluate phase transition temperatures, as well as the thermal effects in PET-G/PEF blends, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA), and Thermogravimetric Analysis (TGA), were performed. Tensile tests revealed that along with an increase in the amount of PEF, an increase in Young's modulus was observed. Besides, the existence of interfacial interactions between polymers, especially in the case of PET-G/PEF 80/20, enabling the PET-G chains to form a network structure with the PEF by reacting with their functional groups, allows observation of a synergistic effect in the improvement of thermal stability and water absorption.

Lipase-Catalyzed Transamidation of Urethane-Bond-Containing Ester

Significant improvement in mechanical properties and shape recovery in polyurethanes can be obtained by cross-linking, usually performed in a traditional chemical fashion. Here, we report model studies of enzymatic transamidations of urethane-bond-containing esters to study the principles of an enzymatic build-up of covalent cross-linked polyurethane networks via amide bond formation. The Lipase-catalyzed transamidation reaction of a urethane-bond-containing model ester ethyl 2-(hexylcarbamoyloxy)propanoate with various amines is discussed. A side product was formed, that could be successfully identified, and its synthesis reduced to a minimum (<1%). Furthermore, a noncatalyzed transamidation that is performed without CalB as the catalyst could be observed. Both observations are due to the known high reactivity of amines with urethane bonds.

A Brønsted Acidic Ionic Liquid as an Efficient and Selective Catalyst System for Bioderived High Molecular Weight Poly(ethylene 2,5-furandicarboxylate)

Green synthesis of bioderived high-molecular-weight poly(ethylene 2,5-furandicarboxylate) (PEF) over metal-free catalysts is a significant challenge. This study focuses on PEF prepared from ethylene glycol and 2,5-furandicarboxylic acid (FDCA) through a direct esterification method with ecofriendly metal-free ionic liquids (ILs) as catalysts. The catalytic activities of a series of imidazolium cations in the presence of various anions are systematically investigated and found to be mainly governed by the anions. Among the ILs studied, 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂ MIM]BF₄ ) is identified as the best catalyst, showing excellent catalytic activity, selectivity, and stability, even at low catalyst loadings (0.1 mol % w.r.t. FDCA). Optimization of the polymerization parameters enables [C₂ MIM]BF₄ -catalyzed production of PEF with a high number-average molecular weight (M_n =5.25×10⁴  g mol^-1 ). The relationship between Brønsted acidity and catalytic activity is also investigated and the results show that the trend in catalytic activity is in good agreement with that in Brønsted acidity, as determined by the Hammett method. Additionally, on the basis of experimental results and density functional theory calculations, an electrophilic activation mechanism induced by hydrogen bonds is proposed. This strategy of adjustable acidity and anion structure in ILs provides an opportunity to develop other ILs for bio-based polyesters through green synthesis pathways.

Multi-Step Enzymatic Synthesis of 1,9-Nonanedioic Acid from a Renewable Fatty Acid and Its Application for the Enzymatic Production of Biopolyesters

1,9-Nonanedioic acid is one of the valuable building blocks for producing polyesters and polyamides. Thereby, whole-cell biosynthesis of 1,9-nonanedioic acid from oleic acid has been investigated. A recombinant Corynebacterium glutamicum, expressing the alcohol/aldehyde dehydrogenases (ChnDE) of Acinetobacter sp. NCIMB 9871, was constructed and used for the production of 1,9-nonanedioic acid from 9-hydroxynonanoic acid, which had been produced from oleic acid. When 9-hydroxynonanoic acid was added to a concentration of 20 mM in the reaction medium, 1,9-nonanedioic acid was produced to 16 mM within 8 h by the recombinant C. glutamicum. The dicarboxylic acid was isolated via crystallization and then used for the production of biopolyester by a lipase. For instance, the polyesterification of 1,9-nonanedioic acid and 1,8-octanediol in diphenyl ether by the immobilized lipase B from Candida antarctica led to formation of the polymer product with the number-average molecular weight (M_n) of approximately 21,000. Thereby, this study will contribute to biological synthesis of long chain dicarboxylic acids and their application for the enzymatic production of long chain biopolyesters.