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A synthetic method for the new chain extenders with different amounts of furan groups and a prepolymer derived from three-furyl diol was developed. A series of polyurethanes cross-linked via the Diels-Alder reaction with various amounts of bismaleimide were produced. The structure, mechanical and thermal properties, and recycling ability of the obtained materials were investigated.

We present here a small series of compounds designed to modify the polymer chain of various polyurethanes in order to introduce a structural fragment with the ability of thermally-triggered reversible covalent interactions. Bismaleimides (2a-2e) were synthesized from commercially available aromatic and aliphatic symmetric diamines (1a-1e) and were further introduced into the Diels-Alder reaction with furfuryl alcohol as dienophiles. The Diels-Alder adducts (3a-3e) were obtained as a mixture of endo- and exo-isomer. The presence of symmetrical hydroxyl groups in the structure of the obtained compounds makes them suitable as chain extenders of low molecular weight diisocyanate prepolymers. The presence of a thermally reversible Diels-Alder reaction adduct in the structure of potential chain-extenders opens a possibility to create unique materials with self-healing properties. All compounds obtained were characterized by 1H, 13C NMR, ESI-HRMS, and IR spectroscopy. The thermochemical parameters of the reverse Diels-Alder reaction were established using DSC analysis.

This work presents a solution to one of the most fundamentally and practically important challenges in the production of silica-based aerogels, time consumption and expensiveness of these processes...

A series of industrial chitosans were analyzed on the presence of residual heavy metals. For the first time, optical microscopy data showed that chitosan solution retained a huge number of insoluble microparticles while transmittance electron microscopy revealed that insoluble fibrous microparticles were incrusted by crystalline nanoparticles with the sizes 5–50 nm. A series of filters used for chitosan solution filtration was analyzed on the presence of retained heavy metal and other residuals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDXS) and mass-spectrometry with inductively coupled plasma (ICP-MS) methods. The SEM-EDXS analysis revealed the presence of Fe residuals together with Si, Al, N and S in the particles found on the filters. ICP-MS analysis found the presence of heavy metals (mainly Fe, Cr and Ni) both on the filter surfaces and in the effluent chitosan solution passed though the filters. This study draws attention to the necessity of a careful selection of industrially manufactured chitosan in order to avoid hidden undesirable effects of chitosan on pharmaceuticals and biomaterials and gives a warning of inapplicability of a stainless-steel made apparatus as a reactor susceptible to caustic soda corrosion for chitin deacetylation and production of medical and food grade chitosan.

A review of the works devoted to the synthesis and investigation of the properties of block copolymers containing fragments of polytetrahydrofuran obtained from renewable natural raw materials is presented. It is shown that the presence of chemically bonded blocks of elastic polytetrahydrofuran in rigid-chain polymer matrices increases their impact resistance and elongation at break, reduces the viscosity of the melt, and improves miscibility with other polymers. It is expected that a similar positive effect of polytetrahydrofuran elastic blocks will be observed in polymer composites filled with dispersed and continuous fibers.

In this work, L-lactide, acting as a cyclic AB monomer, was copolymerized with various AB2 comonomers. Depending on the nature of the AB2 comonomer, it was either a combination of L-lactide ring-opening polymerization with glycidol polymerization or a combination of L-lactide ring-opening polymerization with 2,2-bis (hydroxymethyl) propionic acid (BHP) polycondensation. Both synthetic methods resulted in branched copolyesters. A number of polymers with varying degrees of branching were obtained by systematically changing the proportion of comonomer AB2. The polymers were characterized using 1H NMR spectroscopy and SEC, and their thermal properties were studied using differential scanning calorimetry and thermogravimetric analysis. Also were investigated the viscosity of the solution and the wettability of the branched copolymers. Although structurally similar macromolecules were formed in both synthesis methods, polymers with BHP as AB2 comonomers have higher melting- and glass transition temperatures, higher thermal stability, solution viscosity and lower wettability than polymers with glycidol as AB2 comonomers.

Here we report a combined use of THz-EPR and NMR spectroscopy for obtaining a detailed electronic structure of a long-known high-spin complex, cobalt(II) bis[tris(pyrazolyl)borate]. The lowest inter-Kramers transition was directly measured by THz-EPR spectroscopy, while the energies of higher Kramers doublets were estimated by a recently proposed NMR-based approach. Together, they produced magnetic parameters for a full model that explicitly includes spin–orbit coupling. This approach is applicable to all transition metal ions for which the spin–orbit coupling cannot be treated perturbatively.

Various modifications of epoxy resins with maleimides and polyimide fragments results in the formation of heat-resistant materials with excellent mechanical and electrical properties together with high chemical, corrosion, and radiation resistance. Such materials can be used in the aerospace industry, electronics, instrument making, and other industries. The ability of some epoxy-maleimide resins to react with furanic groups through thermo-reversible Diels-Alder reaction open a new area in composite material science - self-healing binders. Selfhealing materials can restore their structure and mechanical properties after a damage that results in an increase of the service life several times and, therefore, reduce their cost. In this paper, maleimides were modified by diglycidyl ethers to obtain not previously described polyethers, capable of self-healing of mechanical properties after damage. All compounds were characterized by 1H NMR.

A triethyleneglycol-modified epoxy composition based on diglycidylfurfurylamine (FuEp) and 1,1’- (methylene-di-4,1-phenylene)bismaleimide (BMI) was cured with methyl hexahydrophthalic anhydride (MHPPA). The components of the composition can reversely binds through Diels-Alder reaction between furan and maleimide moieties. We studied the effect of TEG additive on the rheological and thermophysical properties of the binder, as well as the ability through thermal treatment. All compounds were characterized with NMR and IR spectroscopy. It was shown that TEG significantly reduces the curing time and the glass transition temperature of the cured samples, which allows to speed up the process of self-healing.

Prepolymer synthesized from toluene-2,4-diisocyanate (TDI) (hard segment), and polypropylene glycol (PPG-2000) (soft segment) was end-capped with difurfurylamine groups. A new cross-linked self-healing polyurethane was obtained via Diels-Alder reaction of the en-capped prepolymer with N,N’-bismaleimido-4,4’-diphenylmethane (BMI). Thermal reversibility of the Diels-Alder reaction (DA-reaction) between terminal furanic rings of the polyurethane prepolymer and bismaleimide cross-linking agent designed to be responsible for self-healing. Polymers were characterized by NMR and IR spectroscopy and thermal analysis (DSC and TGA). Thermal reversibility of the DA-bonds in the cross-linked polymer was confirmed by DSC. The synthesized polymer has good processability and potential recyclability.

New reactive diluents based on bio-renewable raw materials are widely explored as additives to traditional resins. We investigated the effect of furfurylglycidyl ether on the rheological and thermomechanical properties of a widely used epoxy binder with an anhydride hardener. It was shown that the addition of 5-15% active diluent significantly reduces the viscosity of the composition to the values optimal for RTM and vacuum infusion technologies for fiber-reinforced plastics and does not lead to a significant decrease in heat resistance and Young’s modulus of the cured binder

The rheological properties of an epoxy-furan composite incorporating the new low-viscosity furan resin LE828 were studied in the temperature range between 25 and 70°C. Furfural-acetone resin is shown to be an effective and active diluent for epoxy-diane (epoxybisphenol A) resin.