Progress of Polymers from Renewable Resources: Furans, Vegetable Oils, and Polysaccharides

New AB type monomers from lignocellulosic biomass

A series of renewable novel bicyclic AB type polyester precursors have been prepared in good overall yield from lignocellulosic biomass. These advancements take full advantage of the differing oxidation states of functional groups in 5-(hydroxymethyl)furfural by chemoselective preparation of furanic hydroxy esters and applying benzyne-Diels–Alder cycloaddition/aromatization strategies.

Fatty Acid-Based Radically Polymerizable Monomers: From Novel Poly(meth)acrylates to Cutting-Edge Properties

The increasing price of barrels of oil, global warming, and other environmental problems favor the use of renewable resources to replace the petroleum-based polymers used in various applications. Recently, fatty acids (FAs) and their derivatives have appeared among the most promising candidates to afford novel and innovative bio-based (co)polymers because of their ready availability, their low toxicity, and their high versatility. However, the current literature mostly focused on FA-based polymers prepared by condensation polymerization or oxypolymerization, while only a few works have been devoted to radical polymerization due to the low reactivity of FAs through radical process. Thus, the aim of this Review is to give an overview of (i) the most common synthetic pathways reported in the literature to provide suitable monomers from FAs and their derivatives for radical polymerization, (ii) the available radical processes to afford FA-based (co)polymers, and (iii) the different applications in which FA-based (co)polymers have been used since the past few years.

Molecular self-assembly of copolymer from renewable phenols: new class of antimicrobial ointment base

Ointments are highly viscous forms intended for external applications either medicated or non-medicated means. Formulation of ointment depends upon the base ingredients to measure the viscosity difference. Several limitations of ointment bases has been encountered timely as agglomeration, oil phase ingredients can form lumps, poor dispersion, poor drug delivery efficiency, make stained, immiscible, and difficult to wash off. Therefore, it is necessary to make a new type of ointment bases that can overcome those limitations. This review summarizes a new type of ointment base preparation from the copolymer of renewable phenolic derivatives. The nanohydrogel preparation from these copolymers are especially effortless and highly efficient in drug delivery, exhibited versatile biological activities such as antioxidant, anti-inflammatory and wound healing in addition to antimicrobial property. Molecular self-assembly mechanisms have been addressed for nanogel formulation. The strategy makes a significant value in health-care application and be supposed to come marketed soon.

Multivalent and multifunctional polysaccharide-based particles for controlled receptor recognition

Polysaccharides represent a versatile class of building blocks that are used in macromolecular design. By choosing the appropriate saccharide block, various physico-chemical and biological properties can be introduced both at the level of the polymer chains and the resulting self-assembled nanostructures. Here, we synthetized amphiphilic diblock copolymers combining a hydrophobic and helical poly(γ-benzyl-L-glutamate) PBLG and two polysaccharides, namely hyaluronic acid (HA) and laminarin (LAM). The copolymers could self-assemble to form particles in water by nanoprecipitation. In addition, hybrid particles containing both HA and LAM in different ratios were obtained by co-nanoprecipitation of the two copolymers. By controlling the self-assembly process, five particle samples with different morphologies and compositions were developed. The interaction between the particles and biologically relevant proteins for HA and LAM, namely CD44 and Dectin-1 respectively, was evaluated by surface plasmon resonance (SPR). We demonstrated that the particle-protein interaction could be modulated by the particle structure and composition. It is therefore suggested that this method based on nanoprecipitation is a practical and versatile way to obtain particles with controllable interactions with proteins, hence with the appropriate biological properties for biomedical applications such as drug delivery.

Renewable Isohexide-Based, Hydrolytically Degradable Poly(silyl ether)s with High Thermal Stability

Several degradable poly(silyl ether)s (PSEs) have been synthesized by dehydrogenative cross-coupling between bio-based 1,4:3,6-dianhydrohexitols (isosorbide and isomannide) and commercially available hydrosilanes. An air-stable manganese salen nitrido complex [Mn^V N(salen-3,5-tBu₂ )] was employed as the catalyst. High-molecular-weight polymer was obtained from isosorbide and diphenylsilane (M_n up to 17000 g mol^-1 ). Thermal analysis showed that these PSEs possessed high thermal stability with thermal decomposition temperatures (T_-5 % ) of 347-446 °C and glass transition temperatures of 42-120 °C. Structure-property analysis suggested that steric bulk and molecular weight have a significant influence to determine the thermal properties of synthesized polymers. Importantly, these polymers were degraded effectively to small molecules under acidic and basic hydrolysis conditions.

Thinking Green: Sustainable Polymers from Renewable Resources

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Bottle-grade polyethylene furanoate from ring-opening polymerisation of cyclic oligomers

Polyethylene furanoate (PEF) represents a promising renewable resource-based bioplastic as replacement for fossil-based polyethylene terephthalate (PET) with improved material properties. However, the synthesis of PEF through conventional polycondensation remains challenging, since the time-intensive reaction leads to degradation and undesired discolouration of the product. Here we show the successful rapid synthesis of bottle-grade PEF via ring-opening polymerisation (ROP) from cyclic PEF oligomers within minutes, thereby avoiding degradation and discolouration. The melting point of such mixture of cyclic oligomers lies around 370 °C, well above the degradation temperature of PEF (~329 °C). This challenge can be overcome, exploiting the self-plasticising effect of the forming polymer itself (which melts around 220 °C) by initiation in the presence of a high boiling, yet removable, and inert liquid plasticiser. This concept yields polymer grades required for bottle applications (M_n > 30 kg mol⁻¹, conversion > 95%, colour-free products), and can be extended to other diffusion-limited polymer systems.

The synthesis of polyethylene furanoate, a promising renewable resource-based bioplastic, still has challenges. Here the authors show that bottle-grade polyethylene furanoate can be obtained within minutes from ring-opening polymerisation of its cyclic oligomers, thereby avoiding degradation and discolouration.

Lipase-Catalyzed Synthesis of Furan-Based Oligoesters and their Self-Assembly-Assisted Polymerization

We investigate the synthesis of bio-based hydrophilic and hydrophobic oligoesters, which in turn are derived from easily accessible monomers from natural resources. In addition to the selection of renewable monomers, Novozyme 435, an immobilized lipase B from Candida antarctica was used for the oligomerization of monomers. The reaction conditions for oligomerization using Novozyme 435 were established to obtain a moderate-to-good yield. The average number of repeating units and the molecular weight distribution of hydrophilic and hydrophobic oligoester were identified by using NMR spectroscopy, gel-permeation chromatography, and MS. The oligoester derived from a hydrophilic monomer self-assembled to form a viscous solution, which upon further heating resulted in the formation of a polymer by the intermolecular Diels-Alder reaction. The viscosity of the solution and the assembly of oligoester to form a fibrous structure were investigated by using rheological studies, XRD, and SEM. The molecular weight of the cross-linked polymer was identified by using matrix-assisted laser desorption/ionization-MS. The thermal properties of the bio-based polymers were investigated by using thermogravimetric analysis and differential scanning calorimetry. For the first time, the self-assembly-assisted polymerization of an oligoester is reported using the intermolecular Diels-Alder reaction, which opens a new avenue in the field of polymer science.

Compressible, Thermally Insulating, and Fire Retardant Aerogels through Self-Assembling Silk Fibroin Biopolymers Inside a Silica Structure-An Approach towards 3D Printing of Aerogels

Thanks to the exceptional materials properties of silica aerogels, this fascinating highly porous material has found high-performance and real-life applications in various modern industries. However, a requirement for a broadening of these applications is based on the further improvement of the aerogel properties, especially with regard to mechanical strength and postsynthesis processability with minimum compromise to the other physical properties. Here, we report an entirely novel, simple, and aqueous-based synthesis approach to prepare mechanically robust aerogel hybrids by cogelation of silk fibroin (SF) biopolymer extracted from silkworm cocoons. The synthesis is based on sequential processes of acid catalyzed (physical) cross-linking of the SF biopolymer and simultaneous polycondensation of tetramethylorthosilicate (TMOS) in the presence of 5-(trimethoxysilyl)pentanoic acid (TMSPA) as a coupling agent and subsequent solvent exchange and supercritical drying. Extensive characterization by solid-state ¹H NMR, ²⁹Si NMR, and 2D ¹H-²⁹Si heteronuclear correlation (HETCOR) MAS NMR spectroscopy as well as various microscopic techniques (SEM, TEM) and mechanical assessment confirmed the molecular-level homogeneity of the hybrid nanostructure. The developed silica-SF aerogel hybrids contained an improved set of material properties, such as low density (ρ_b,average = 0.11-0.2 g cm^-3), high porosity (∼90%), high specific surface area (∼400-800 m² g^-1), and excellent flexibility in compression (up to 80% of strain) with three orders of magnitude improvement in the Young's modulus over that of pristine silica aerogels. In addition, the silica-SF hybrid aerogels are fire retardant and demonstrated excellent thermal insulation performance with thermal conductivities (λ) of 0.033-0.039 W m^-1 K^-1. As a further advantage, the formulated hybrid silica-SF aerogel showed an excellent printability in the wet state using a microextrusion-based 3D printing approach. The printed structures had comparable properties to their monolith counterparts, improving postsynthesis processing or shaping of the silica aerogels significantly. Finally, the hybrid silica-SF aerogels reported here represent significant progress for a mechanically customized and robust aerogel for multipurpose applications, namely, as a customized thermal insulation material or as a dual porous open-cell biomaterial used in regenerative medicine.

Enzymatic Polymerization of Dimethyl 2,5-Furandicarboxylate and Heteroatom Diamines

Previously, we have synthesized a diverse range of 2,5-furandicarboxylic acid (FDCA)-based semiaromatic polyamides via enzymatic polymerization. This novel class of polymers are biobased alternatives to polyphthalamides, which are petrol-based semiaromatic polyamides. From a commercial perspective, they have interesting properties as high-performance materials and engineering thermoplastics. It is even more appealing to explore novel FDCA-based polyamides with added functionality, for the development of sustainable functional materials. Here, a set of FDCA-based heteroatom polyamides have been successfully produced via Novozyme 435 (N435)-catalyzed polymerization of biobased dimethyl 2,5-furandicarboxylate with (potentially)heteroatom diamines, namely, 4,9-dioxa-1,12-dodecanediamine (DODA), diethylenetriamine, and 3,3-ethylenediiminopropylamine. We performed the enzymatic polymerization in solution and bulk. The latter approach is more sustainable and results in higher molecular weight products. Among the tested heteroatom diamines, N435 shows the highest catalytic activity toward DODA. Furthermore, we find that all obtained FDCA-based heteroatom polyamides are amorphous materials with a relatively high thermal stability. These heteroatom polyamides display a glass-transition temperature ranging from 41 to 107 °C.

Opening Furan for Tailoring Properties of Bio-based Poly(Furfuryl Alcohol) Thermoset

This work shows how furan ring-opening reactions were controlled by polymerization conditions to tune the cross-link density in bio-based poly(furfuryl alcohol) (PFA). The influence of water and isopropyl alcohol (IPA) on the polymerization of furfuryl alcohol, and particularly on furan ring-opening, was investigated by means of ¹³ C NMR and FT-IR spectroscopy. Results indicated that formation of open structures were favored in the presence of solvents, thus leading to modification of the thermo-mechanical properties compared to PFA cross-linked without solvent. Dynamic mechanical analyses showed that when slightly more open structures were present in PFA it resulted in an important decrease of the cross-link density. Despite lower glass-transition temperature and lower elastic modulus for PFA polymerized with solvent, the thermal stability remains very high (>350 °C) even with more open structures in PFA.

FA Polymerization Disruption by Protic Polar Solvents

Furfuryl alcohol (FA) is a biobased monomer derived from lignocellulosic biomass. The present work describes its polymerization in the presence of protic polar solvents, i.e., water or isopropyl alcohol (IPA), using maleic anhydride (MA) as an acidic initiator. The polymerization was followed from the liquid to the rubbery state by combining DSC and DMA data. In the liquid state, IPA disrupts the expected reactions during the FA polymerization due to a stabilization of the furfuryl carbenium center. This causes the initiation of the polymerization at a higher temperature, which is also reflected by a higher activation energy. In the water system, the MA opening allows the reaction to start at a lower temperature. A higher pre-exponential factor value is obtained in that case. The DMA study of the final branching reaction occurring in the rubbery state has highlighted a continuous increase of elastic modulus until 290 °C. This increasing tendency of modulus was exploited to obtain activation energy dependences (E_α) of FA polymerization in the rubbery state.

Partially Renewable Poly(butylene 2,5-furandicarboxylate-co-isophthalate) Copolyesters Obtained by ROP

Cyclic butylene furandicarboxylate (c(BF)_n) and butylene isophthalate (c(BI)_n) oligomers obtained by high dilution condensation reaction were polymerized in bulk at 200 °C with Sn(Oct)₂ catalyst via ring opening polymerization to give homopolyesters and copolyesters (coPBF_xI_y) with weight average molar masses in the 60,000⁻70,000 g·mol^-1 range and dispersities between 1.3 and 1.9. The composition of the copolyesters as determined by NMR was practically the same as that of the feed, and they all showed an almost random microstructure. The copolyesters were thermally stable up to 300 °C and crystalline for all compositions, and have T_g in the 40⁻20 °C range with values decreasing almost linearly with their content in isophthalate units in the copolyester. Both melting temperature and enthalpy of the copolyesters decreased as the content in butylene isophthalate units increased up to a composition 30/70 (BF/BI), at which the triclinic crystal phase made exclusively of butylene furanoate units changed to the crystal structure of PBI. The partial replacement of furanoate by isophthalate units decreased substantially the crystallizability of PBF.

Solid-State Polymerization of Poly(Ethylene Furanoate) Biobased Polyester, II: An Efficient and Facile Method to Synthesize High Molecular Weight Polyester Appropriate for Food Packaging Applications

The goal of this study was to synthesize, through a facile strategy, high molecular weight poly(ethylene furanoate) (PEF), which could be applicable in food packaging applications. The efficient method to generate PEF with high molecular weight consists of carrying out a first solid-state polycondensation under vacuum for 6 h reaction time at 205 °C for the resulting polymer from two-step melt polycondensation process, which is catalyzed by tetrabutyl titanate (TBT). A remelting step was thereafter applied for 15 min at 250 °C for the obtained polyester. Thus, the PEF sample was ground into powder, and was then crystallized for 6 h at 170 °C. This polyester is then submitted to a second solid-state polycondensation (SSP) carried out at different reaction times (1, 2, 3.5, and 5 h) and temperatures 190, 200, and 205 °C, under vacuum. Ultimately, a significant increase in intrinsic viscosity is observed with only 5 h reaction time at 205 °C during the second SSP being needed to obtain very high molecular weight PEF polymer greater than 1 dL/g, which sufficient for manufacturing purposes. Intrinsic viscosity (IV), carboxyl end-group content (⁻COOH), and thermal properties, via differential scanning calorimetry (DSC), were measured for all resultant polyesters. Thanks to the post-polymerization process, DSC results showed that the melting temperatures of the prepared PEF samples were steadily enhanced in an obvious way as a function of reaction time and temperature increase. It was revealed, as was expected for all SSP samples, that the intrinsic viscosity and the average molecular weight of PEF polyester increased with increasing SSP time and temperature, whereas the number of carboxyl end-group concentration was decreased. A simple kinetic model was also developed and used to predict the time evolution of polyesters IV, as well as the carboxyl and hydroxyl end-groups of PEF during the SSP.

Biocatalytic Route for the Synthesis of Oligoesters of Hydroxy-Fatty acids and ϵ-Caprolactone

Developments of past years placed the bio-based polyesters as competitive substitutes for fossil-based polymers. Moreover, enzymatic polymerization using lipase catalysts has become an important green alternative to chemical polymerization for the synthesis of polyesters with biomedical applications, as several drawbacks related to the presence of traces of metal catalysts, toxicity and higher temperatures could be avoided. Copolymerization of ϵ-caprolactone (CL) with four hydroxy-fatty acids (HFA) from renewable sources, 10-hydroxystearic acid, 12-hydroxystearic acid, ricinoleic acid, and 16-hydroxyhexadecanoic acid, was carried out using commercially available immobilized lipases from Candida antarctica B, Thermomyces lanuginosus, and Pseudomonas stutzeri, as well as a native lipase. MALDI-TOF-MS and 2D-NMR analysis confirmed the formation of linear/branched and cyclic oligomers with average molecular weight around 1200 and polymerization degree up to 15. The appropriate selection of the biocatalyst and reaction temperature allowed the tailoring of the non-cyclic/cyclic copolymer ratio and increase of the total copolymer content in the reaction product above 80%. The catalytic efficiency of the best performing biocatalyst (Lipozyme TL) is evaluated during four reaction cycles, showing excellent operational stability. The thermal stability of the reaction products is assessed based on TG and DSC analysis. This new synthetic route for biobased oligomers with novel functionalities and properties could have promising biomedical applications.