Carbamation of Starch with Amine Using Dimethyl Carbonate as Coupling Agent

A one-pot coupling of starch with alkyl amine was studied using dimethyl carbonate (DMC) as the coupling agent. Although reaction occurred without a catalyst (24 h, 70 °C), different catalysts, namely, imidazole, tetramethylguanidine, 1,8-diazabicyclo[5.4.0]­undec-7-ene (DBU), and combinations thereof were investigated to improve the reaction efficiency. When 20 mol % DBU was used as a catalyst, the degree of substitution (DS) could be improved from 0.05 to 0.15 compared to the noncatalyzed reaction. When the amount of DBU was decreased to 5 mol %, catalytical activity remained, albeit with a slightly lower DS (0.09). Temperature did not have a significant effect on the DS but it could be used to alter the solubility of the product. Based on chemical analysis, the alkyl group was attached to starch by the formation of a carbamate group. As the carbonyl carbon in the carbamate originated from DMC, which, in turn, can be produced from carbon dioxide on an industrial scale, the current study provides a conventional way to utilize carbon dioxide-based chemicals in the functionalization of a natural polymer. DMC is also biodegradable and classified as a nonvolatile organic component, making it an environmentally desirable coupling agent

Renewable Furfural-Based Polyesters Bearing Sulfur-Bridged Difuran Moieties with High Oxygen Barrier Properties

With the goal of achieving high barrier with bio-based materials, for example, for packaging applications, a series of novel furfural-based polyesters bearing sulfide-bridged difuran dicarboxylic acid units with high oxygen barrier properties were synthesized and characterized. For the novel poly­(alkylene sulfanediyldifuranoate)­s, a 11.2–1.9× higher barrier improvement factor compared to amorphous poly­(ethylene terephthalate) was observed which places the novel polyesters in the top class among previously reported 2,5-furandicarboxylic acid (FDCA) and 2,2′-bifuran-based polyesters. Titanium-catalyzed polycondensation reactions between the novel synthesized monomer, dimethyl 5,5′-sulfanediyldi­(furan-2-carboxylate), and four different diols, ethylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,5-pentanediol, afforded difuran polyesters with high intrinsic viscosities (0.76–0.90 dL/g). These polyesters had good thermal stability, decomposing at 342–363 and 328–570 °C under nitrogen and air, respectively, which allowed processing them into free-standing films via melt-pressing. In tensile testing of the film specimens, tensile moduli in the range of 0.4–2.6 GPa were recorded, with higher values observed for the polyesters with shorter diol units. Interestingly, besides the low oxygen permeability, the renewable sulfide-bridged furan monomer also endowed the polyesters with slight UV shielding effect, with cutoff wavelengths of ca. 350 nm, in contrast to FDCA-based polyesters, which lack significant UV light absorption at over 300 nm

High-Barrier Biobased Copolyesters with Targeted Glass Transition Temperatures as Renewable Alternatives for PET

A series of amorphous furan-based copolyesters were investigated with the goal of matching the glass transition temperature (Tg) of poly­(ethylene terephthalate) (PET) while providing an enhanced O2 barrier. The biobased copolyesters were composed of dimethyl 5,5′-sulfanediyldi­(furan-2-carboxylate) (DM-SFA) with either dimethyl 2,5-furandicarboxylate (DM-FDCA) or dimethyl 2,2′-bifuran-5,5′-dicarboxylate (DM-BFDCA) as the main monomers with ethylene glycol as the diol component. The furfural-based monomers DM-SFA and DM-BFDCA in roughly equimolar ratios provided copolyesters with Tg in the range of PET, while also having low O2 and UV-light permeabilities. With the 5-hydroxy­methylfurfural-based DM-FDCA monomer, DM-SFA was adjusted to be the minor comonomer in the feed in order to provide PET-like Tg for the copolyester. On the other hand, the O2 permeabilities of these copolyesters were substantially lower, although the DM-FDCA monomer lacked the UV-blocking benefits of DM-BFDCA. Finally, isosorbide (IS) was also investigated as a possible Tg-enhancing comonomer in conjunction with ethylene glycol and DM-SFA. However, thermal stability of the IS-containing copolyester was found to be lower, as indicated by thermogravimetric analysis. Incomplete dissolution after polycondensation was also observed, which was consistent with cross-linking under high-temperature conditions. Additionally, melt-pressed films did not completely yield at high temperatures during dynamic mechanical analysis, which contrasted with the behavior of the DM-FDCA and DM-BFDCA copolyesters. The DM-SFA/DM-BFDCA copolyesters were identified as especially interesting materials having relatively high glass transition temperatures while being completely amorphous and providing films with low O2 and UV-light permeabilities. They are also notable for having most of their carbon derived from the renewable platform chemical furfural

Flexible Furfural-Based Barrier Polyester from a Self-Condensable Monomer

A novel biobased sulfur-bridged polyester, with high oxygen barrier properties, was synthesized via self-condensation of a new AB-type furfural-based monomer, i.e., methyl 5-[(2-hydroxyethyl)­sulfanyl]­furan-2-carboxylate (MSF). The novel MSF-based polyester (pMSF) showed a 15× higher barrier improvement factor compared to amorphous poly­(ethylene terephthalate) (PET) and good UV light filtering, with a cutoff wavelength of ca. 340 nm, thanks to the introduced sulfur heteroatom. Interestingly, pMSF offers a circular life cycle, with excellent chemical recyclability. Furthermore, the new self-condensable monomer, MSF, was utilized as a comonomer to improve the O2 barrier performance of poly­(ethylene furanoate) (PEF) and poly­(ethylene bifuranoate) (PEBF). The new copolymers, i.e., PEF80MSF20 and PEBF80MSF20, have been characterized by structural, thermal, mechanical, and barrier measurements. The results clearly show that the novel monomer, MSF, is a promising precursor for sustainable biobased packaging materials with benefits of high O2 barrier, UV light filtering, flexibility, and chemical recyclability

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

Syntheses of Thiophene and Thiazole-Based Building Blocks and Their Utilization in the Syntheses of A‑D‑A Type Organic Semiconducting Materials with Dithienosilolo Central Unit

Dithienosilole moiety is an electron donating unit, and it has been applied, for example, as a part of small molecular and polymeric electron donors in high performance organic photovoltaic cells. Herein, we report efficient synthetic routes to two symmetrical, dithienosilolo-central-unit-based A-D-A type organic semiconducting materials DTS­(Th2FBTTh)2 and DTS­(ThFBTTh)2. Fine-tuned conditions in Suzuki–Miyaura couplings were tested and utilized. The effect of inserting additional hexylthiophene structures symmetrically into the material backbone was investigated, and it was noted that contrary to commonly accepted fact, the distance between electron donor and acceptor seems to play a bigger role in lowering the Egap value of the molecule than just extending the length of the conjugated backbone. We searched for precedent cases from the literature, and these are compared to our findings. The optical properties of the materials were characterized with UV–vis spectroscopy. Majority of the intermediate compounds along the way to final products were produced with excellent yields. Our results offer highly efficient routes to many heterocyclic structures but also give new insights into the design of organic semiconducting materials

Utilizing Furfural-Based Bifuran Diester as Monomer and Comonomer for High-Performance Bioplastics: Properties of Poly(butylene furanoate), Poly(butylene bifuranoate), and Their Copolyesters

Two homopolyesters and a series of novel random copolyesters were synthesized from two bio-based diacid esters, dimethyl 2,5-furandicarboxylate, a well-known renewable monomer, and dimethyl 2,2′-bifuran-5,5′-dicarboxylate, a more uncommon diacid based on biochemical furfural. Compared to homopolyesters poly­(butylene furanoate) (PBF) and poly­(butylene bifuranoate) (PBBf), their random copolyesters differed dramatically in that their melting temperatures were either lowered significantly or they showed no crystallinity at all. However, the thermal stabilities of the homopolyesters and the copolyesters were comparable. Based on tensile tests from amorphous film specimens, it was concluded that the elastic moduli, tensile strengths, and elongation at break values for all copolyesters were similar as well, irrespective of the furan:bifuran molar ratio. Tensile moduli of approximately 2 GPa and tensile strengths up to 66 MPa were observed for amorphous film specimens prepared from the copolyesters. However, copolymerizing bifuran units into PBF allowed the glass transition temperature to be increased by increasing the amount of bifuran units. Besides enhancing the glass transition temperatures, the bifuran units also conferred the copolyesters with significant UV absorbance. This combined with the highly amorphous nature of the copolyesters allowed them to be melt-pressed into highly transparent films with very low ultraviolet light transmission. It was also found that furan–bifuran copolyesters could be as effective, or better, oxygen barrier materials as neat PBF or PBBf, which themselves were found superior to common barrier polyesters such as PET

High Oxygen Barrier Polyester from 3,3′-Bifuran-5,5′-dicarboxylic Acid

An exceptional oxygen barrier polyester prepared from a new biomass-derived monomer, 3,3′-bifuran-5,5′-dicarboxylic acid, is reported. When exposed to air, the furan-based polyester cross-links and gains O2 permeability 2 orders of magnitude lower than initially, resulting in performance comparable to the best polymers in this class, such as ethylene-vinyl alcohol copolymers. The cross-links hinder the crystallization of amorphous samples, also rendering them insoluble. The process was observable via UV–vis measurements, which showed a gradual increase of absorbance between wavelengths of 320 and 520 nm in free-standing films. The structural trigger bringing about these changes appears subtle: the polyester containing 5,5′-disubstituted 3,3′-bifuran moieties cross-linked, whereas the polyester with 5,5′-disubstituted 2,2′-bifuran moieties was inert. The 3,3′-bifuran-based polyester is effectively a semicrystalline thermoplastic, which is slowly converted into a cross-linked material with intriguing material properties once sufficiently exposed to ambient air

Synthesis of 4-Alkoxy-8-hydroxyquinolines^†

Quinolines with a hydroxyl group at the 8-position and an alkoxy group at the 4-position are rare compounds. In this paper the synthesis of five 4-alkoxy-8-hydroxyquinolines is reported. The key reaction in the synthetic route is a selective protection of the hydroxyl group at C-atom 8 in 4,8-dihydroxyquinoline with a tosyl group and the hydrolytic removal of the protective group after the alkylation. The tosyl group is stable during the alkylations with various alkylating agents in the presence of sodium hydride

Carboxymethyl Chitosan and Its Hydrophobically Modified Derivative as pH-Switchable Emulsifiers

The emulsification properties of carboxymethyl chitosan (CMChi) and hydrophobically modified carboxymethyl chitosan (h-CMChi) were studied as a function of pH and dodecane/water ratio. The pH was varied between 610, and the oil/water ratio between 0.12.0. In CMChi solution, the emulsion stability increased as the pH was lowered from 10 to 7, and the phase inversion was shifted from oil/water ratio 1.0 to 1.8, respectively. The system behaved differently in pH 6 due to the aggregation of CMChi and the formation of nanoparticles (∼200300 nm). No phase inversion was observed and the maximum amount of emulsified oil was reached at oil/water ratio 1.2. The h-CMChi showed similar behavior as a function of pH but, due to hydrophobic modification, the phase inversion was shifted to higher values in pH 710. In pH 6, the behavior was similar, but the maximum amount of emulsified oil was higher compared to CMChi. The amount of adsorbed particles correlated with the emulsified amount of oil. Reversible emulsification of dodecane was demonstrated by pH adjustment using CMChi and h-CMChi solutions. The formed emulsions were gel-like, suggesting particle–particle interaction