Shanmugam Thiyagarajan

Biobased furandicarboxylic acids (FDCAs): effects of isomeric substitution on polyester synthesis and properties

In this study we present the application of different isomers of furandicarboxylic acid, or FDCA, obtained from agro-residues, in polyester synthesis. New polyesters based on 2,4-FDCA and 3,4-FDCA isomers with (linear) diols were thoroughly characterised and compared with their as-synthesised 2,5-FDCA analogues. All polymers were obtained by melt polycondensation of linear diols with FDCA dimethyl esters and exhibit molecular weights in the range Mw = 34000–65000 and polydispersities close to 2.0. Thermogravimetric analysis (TGA) of the new polyesters shows that they have comparable or even higher thermal stability compared to the 2,5-FDCA polyesters. Interestingly, the glass-transition temperatures (Tg) of 2,4-FDCA derived polyesters are similar to those of the 2,5-FDCA isomers. Both differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) analyses showed that 2,4-PEF is amorphous, while 2,5-PEF and 3,4-PEF are semi-crystalline materials.

Isohexide Derivatives from Renewable Resources as Chiral Building Blocks

The combination of rapidly depleting fossil resources and growing concerns about greenhouse gas emissions and global warming have stimulated extensive research on the use of biomass for energy, fuels, and chemicals.[1] Although biobased chemicals have the potential to reduce the amount of fossil feedstock consumed in the chemical industry today, the most abundant type of biobased feedstock, that is, carbohydrates, is often unsuitable for current high-temperature industrial chemical processes. Compared to hydrophobic aliphatic or aromatic feedstocks with a low degree of functionalization, carbohydrates such as polysaccharides are complex, overfunctionalized hydrophilic materials. One approach to overcome these drawbacks is to reduce the number of functional groups, resulting in more stable, industrially applicable bifunctional biobased building blocks,[2] such as furan-2,5-dicarboxylic acid,[3] levulinic acid,[4] and isosorbide.[5] Isosorbide (1,4:3,6-dianhydrosorbitol) is a rigid bicyclic diol that is derived from sorbitol and can ultimately be obtained from glucose-based polysaccharides such as starch and cellulose.[6] Apart from isosorbide, in which the hydroxyl groups on C2 and C5 are in the exo and endo positions, respectively, two other isohexides are known (Figure 1): the symmetrical endo-endo isomer isomannide (1,4:3,6-dianhydromannitol) and the exo-exo isomer isoidide (1,4:3,6-dianhydroiditol), derived from d-mannitol and l-iditol, respectively.

Renewable Rigid Diamines: Efficient, Stereospecific Synthesis of High Purity Isohexide Diamines

We report an efficient three-step strategy for synthesizing rigid, chiral isohexide diamines derived from 1,4:3,6-dianhydrohexitols. These biobased chiral building blocks are presently the subject of several investigations (in our and several other groups) because of their application in high-performance biobased polymers, such as polyamides and polyurethanes. Among the three possible stereo-isomers, dideoxy-diamino isoidide and dideoxy-diamino isosorbide can be synthesized from isomannide and isosorbide respectively in high yield with absolute stereo control. Furthermore, by using this methodology dideoxy-amino isomannide-a tricyclic adduct-was obtained starting from isoidide in high yield. Our improved synthetic route is a valuable advance towards meeting scale and purity demands for evaluating the properties of new biobased performance materials, which will benefit the development of these plastics.

Semi-Aromatic Polyesters Based on a Carbohydrate- Derived Rigid Diol for Engineering Plastics

New carbohydrate-based polyesters were prepared from isoidide-2,5-dimethanol (extended isoidide, XII) through melt polymerization with dimethyl esters of terephthalic acid (TA) and furan-2,5-dicarboxylic acid (FDCA), yielding semi-crystalline prepolymers. Subsequent solid-state post-condensation (SSPC) gave high molecular weight (Mn =30 kg mol(-1) for FDCA) materials, the first examples of high Mn , semi-aromatic homopolyesters containing isohexide derivatives obtained via industrially relevant procedures. NMR spectroscopy showed that the stereo-configuration of XII was preserved under the applied conditions. The polyesters are thermally stable up to 380 °C. The TA- and FDCA-based polyesters have high Tg (105 °C and 94 °C, resp.) and Tm (284 °C and 250 °C, resp.) values. Its reactivity, stability, and ability to afford high Tg and Tm polyesters make XII a promising diol for the synthesis of engineering polymers.

Concurrent formation of furan-2,5- and furan-2,4-dicarboxylic acid: unexpected aspects of the Henkel reaction

The concurrent formation of furan-2,5- and furan-2,4-dicarboxylic acid under solvent free conditions via a disproportionation reaction is described. By reacting potassium-2-furoate at 260 °C in the presence of 22 mol% of (Lewis acidic) catalysts like CdI2 or ZnCl2, potassium-2-furoate is disproportionated to furan and furandicarboxylic acids. Besides furan and furan-2,5-dicarboxylic acid (2,5-FDCA) as the main products, furan-2,4-dicarboxylic acid (2,4-FDCA) is also formed as a by-product. Experimental evidence has been obtained that, under the reaction conditions applied, 2,5-FDCA and 2,4-FDCA are formed by separate reaction pathways. Selectivity towards the different FDCA isomers is affected by the type of catalyst used. Single-crystal X-ray analysis shows that 2,4-FDCA has a more ‘linear’ character compared to 2,5-FDCA and hence is structurally more comparable to terephthalic acid (TA), making it an interesting monomer for synthetic polyesters.

Isohexide hydroxy esters: synthesis and application of a new class of biobased AB-type building blocks

Here we present the synthesis of a new family of sugar derived 1,4:3,6-dianhydrohexitol based AB-type monomers, containing one methyl ester group and a secondary hydroxyl group in all four possible stereo isomers (RR, RS, SR, SS). Structural characterization of the monomers (5a–d) was established by 1D and 2D NMR analysis, which was further confirmed by single-crystal X-ray structure determination. The application of these monomers in step-growth polymerization afforded fully isohexide based stereo-regular polyesters. Homo polyesters based on the RR and RS monomers were obtained with reasonable molecular weights by melt polymerization (Mn 2400 and 2500 resp.). These materials showed unexpectedly low glass-transition temperatures of 20 °C and 15 °C respectively. In contrast, the monomers with SR and SS configuration yielded only low molecular weight oligomers. Surprisingly, copolymerization of the RR and SR monomers gave a polyester with higher molecular weight (Mn 4100) and a high Tg of 80 °C. These preliminary results show that isohexide hydroxyesters are an intriguing new class of biobased building blocks with many potential applications.

Towards sugar-derived polyamides as environmentally friendly materials

As part of our ongoing study investigating isohexide-based polyamides, we have synthesized isosorbide(bis(propan-1-amine)) (DAPIS) and studied its reactivity in the polymerization towards fully biobased polyamides. Polycondensation of nylon salts with various contributions of DAPIS afforded a family of homo- and copolyamides, which were characterized using complementary spectroscopic techniques. The chemical structure of the materials was determined by FT-IR, 1D and 2D liquid-state NMR spectroscopy, whilst the supramolecular arrangement, conformational changes upon heating, and molecular mobility of the polymers were investigated by solid-state 13C{1H} Cross-Polarization/Magic-Angle Spinning (CP/MAS) NMR and 13C{1H} Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) experiments. The abundance of the different DAPIS conformers was determined by DFT-D computational methods. The thermal properties of the polyamides were tested for polymers with different amounts of isohexide units in the backbone by DSC and TGA, demonstrating that the increasing amounts of isohexide diamines efficiently decrease their melting points and slightly decrease their thermal stability. The relaxation processes of the isohexide-derived polyamides were studied by DMTA.

Fully Renewable Thermoplastic Poly(ester urethane urea)s from Bio-based Diisocyanates

A series of fully renewable poly(ester urethane urea)s (PEUs) were synthesized from bio-based starting materials, e.g., the polyester diol, the diisocyanates including L-lysine diisocyanate (LDI) and isoidide diisocyanate (IIDI), the chain-extenders including 1,4-diaminobutane (bDA), diaminoisoidide (iDA) and di(aminobutyl) urea (b2DA). It is found that the PEU based on the novel diisocyanate, IIDI, exhibits satisfactory thermal and mechanical properties. The LDI-based PEUs show less favorable thermal and mechanical properties than the IIDI-based counterpart, since the chemical structure of LDI is less regular than that of IIDI. However, by introducing a urea-containing dimeric diamine (b2DA) instead of the monomeric diamines, the properties of the LDI-based PEU can be improved significantly. For instance, the flow temperature increases 100°C and the E-modulus also increases from 1 MPa to approximately 20 MPa. These fully renewable PEUs seem to be interesting materials and they can potentially be used in biomedical or packaging applications.

Isohexide Dinitriles: A Versatile Family of Renewable Platform Chemicals

Building blocks of isohexides extended by one carbon atom at the 2- or 5-positions are now synthetically accessible by a convenient, selective, base-catalyzed epimerization of the corresponding dinitriles. Kinetic experiments using the strong organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) show that all three possible isohexide dinitrile isomers exist within a dynamic equilibrium. An epimerization mechanism based on density functional theory (DFT) calculations is proposed. Structural identification of all three possible isomers is based on NMR analysis and single crystal x-ray crystallography. DFT calculations confirm that the observed crystal structures are indeed the lowest energy conformers of these isohexide derivatives.