The study investigates the kinetics and thermodynamics of the reversible tandem Diels-Alder (tDA) reaction between difuranic compounds and maleimides, leading to the quantitative formation of tDA adducts at rates comparable to their counterparts from the “classical” Diels-Alder (DA) reaction. The tDA adducts exhibited unprecedented thermal stability up to 250 °C, which is 100 °C higher than that of the DA adducts, owing to the higher activation energy (Ea) required for the initial intramolecular step of the reverse process. The stability of the tDA adducts was exploited in the AA + BB type polymerization of tetrafuranic monomers with bis(maleimides), yielding thermally stable (up to 200 °C) yet depolymerasable linear polymers with molecular weights of 10-20 kDa. Only furanic groups were identified as the end-groups of the resulting polymers, suggesting the possibility for post-polymerization and end-group modifications. NMR and GPC kinetic data offered insights into the intermediate formation of classical adducts during polymerization, as well as the stereochemistry of tDA adducts in the polymer chains. Combined thermal analysis (DSC, TGA, and TMA) provided a comprehensive understanding of the reverse DA reaction in the resulting materials. This relatively clean, catalyst- and byproduct-free, well-controlled process, which uses derivatives of biorenewables as monomers, heralds the formation of a new class of thermally recyclable polymers.

The repair efficiency of various self-healing materials often depends on the ability of the prepolymer and curing agent to form mixtures. This paper presents a synthesis and study of the properties of modified self-healing polyurethanes using the Diels–Alder reaction (DA reaction), obtained from a maleimide-terminated preform and a series of furan–urethane curing agents. The most commonly used isocyanates (4,4′-methylene diphenyl diisocyanate (MDI), 2,4-tolylene diisocyanate (TDI), and hexamethylene diisocyanate (HDI)) and furan derivatives (furfurylamine, difurfurylamine, and furfuryl alcohol) were used as initial reagents for the synthesis of curing agents. For comparative analysis, polyurethanes were also obtained using the well-known “traditional” approach—from furan-terminated prepolymers based on mono- and difurfurylamine, as well as furfuryl alcohol and the often-used bismaleimide curing agent 1,10-(methylenedi-1,4-phenylene)bismaleimide (BMI). The structure and composition of all polymers were studied using spectroscopic methods. Molecular mass was determined using gel permeation chromatography (GPC). Thermal properties were studied using TGA, DSC, and TMA methods. The mechanical and self-healing properties of the materials were investigated via a uniaxial tensile test. Visual assessment of the completeness of damage restoration after the self-healing cycle was carried out using a scanning electron microscope. It was shown that the proposed modified approach helps obtain more durable polyurethanes with a high degree of self-healing of mechanical properties after damage.

On the basis of furfuryl glycidyl ether, the product derived from furfural, diol chain extenders have been synthesized. Using these chain extenders and bismaleimide as a crosslinker polyurethanes with thermally induced self-healing effect have been prepared by the reversible Diels–Alder reaction. The structure of the synthesized polymers is studied by IR spectroscopy. Thermal and physicomechanical properties of the materials are also investigated. Differential scanning calorimetry measurements revealed the cyclic nature of direct and retro-Diels–Alder reactions. Visual assessment of the self-healing ability of the material is carried out using scanning electron microscopy. Quantitative evaluation (the self-healing efficiency of the Young’s modulus and strength) is performed by means of dynamometric analysis of initial and recovered polymer samples. It has been demonstrated that the content of dynamic bonds affects the properties of polyurethanes, as well as the efficiency of self-healing.

В связи с растущим спросом на функциональные полимерные материалы особое внимание уделяется их износостойкости и сроку службы. Эти характеристики могут ухудшаться из-за возникновения микроповреждений. Способом их устранения является использование самовосстанавливающихся полимерных связующих, в которых повреждения залечиваются под воздействием определенных условий-инициаторов (УФ-излучение, нагрев, давление и т. д.).

The work is aimed at studying the impact resistance of epoxy oligomer matrices (EO) modified with polysulfone (PSU) or polyethersulfone (PES) and glass fibers reinforced plastics (GFRP) based on them under low-velocity impact conditions. The concentration dependences of strength and fracture energy of modified matrices and GFRP were determined. It has been determined that the type of concentration curves of the fracture energy of GFRP depends on the concentration and type of the modifying polymer. It is shown that strength σ and fracture energy EM of thermoplastic-modified epoxy matrices change little in the concentration range from 0 to 15 wt.%. However, even with the introduction of 20 wt.% PSU into EO, the strength increases from 164 MPa to 200 MPa, and the fracture energy from 32 kJ/m2 to 39 kJ/m2. The effect of increasing the strength and fracture energy of modified matrices is retained in GFRP. The maximum increase in shear strength (from 72 MPa to 87 MPa) is observed for GFRP based on the EO + 15 wt.% PSU matrix. For GFRP based on EO + 20 wt.% PES, the shear strength is reduced to 69 MPa. The opposite effect is observed for the EO + 20 wt.% PES matrix, where the strength value decreases from 164 MPa to 75 MPa, and the energy decreases from 32 kJ/m2 to 10 kJ/m2. The reference value for the fracture energy of GFRP 615 is 741 kJ/m2. The maximum fracture energy for GFRP is based on EO + 20 wt.% PSU increases to 832 kJ/m2 for GFRP based on EO + 20 wt.% PES-up to 950 kJ/m2. The study of the morphology of the fracture surfaces of matrices and GFRP confirmed the dependence of impact characteristics on the microstructure of the modified matrices and the degree of involvement in the process of crack formation. The greatest effect is achieved for matrices with a phase structure "thermoplastic matrix-epoxy dispersion." Correlations between the fracture energy and strength of EO + PES matrices and GFRP have been established.

The authors have proposed the novel approach for evaluation of the self-healing effect in carbon fiber reinforced plastics (CFRP) on micro- and macro samples, using the dynamic mechanical analysis (DMA) and the double-cantilever beam delamination methods, respectively. A modified epoxy resin with a self-healing effect was used as the matrix for carbon plastics. The flexural modulus E' of microsamples with delamination and the specific delamination energy (crack resistance) G(IR) of macrosamples with a given initial crack were chosen as criteria for evaluating the self-healing of carbon plastics. The sensitivity of the E' and G(IR) parameters to the applied initial crack is shown. The value of the elastic modulus E' with the initial crack can be reduced up to two times compared to the E' values for the control materials, depending on the length of the initial crack. The degree of recovery of E' for CFRP with a microcrack varies from 91 to 118%. A high degree of healing could be achieved in 48 h. The G(IR) value of CFRP samples with a given macroseparation after heat treatment is 7% of the initial G(IR) value (0.7 kJ/m(2)). Recovery of delaminations for microsamples is more efficient than for macrosamples. The study of CFRP cracks by X-ray tomography before and after self-healing showed that the crack "overgrows" during the heat treatment cycle, and the defects (pores) formed during the manufacture of the sample decrease in size.

The healing efficiency in self-healing materials is bound by the ability to form blends between the prepolymer and curing agent. One of the problems in the development of self-healing polymers is the reduced affinity of the bismaleimide curing agent for the elastomeric furan-containing matrix. Even when stoichiometric amounts of both components are applied, incompatibility of components can significantly reduce the effectiveness of self-healing, and lead to undesirable side effects, such as crystallization of the curing agent, in the thickness and on the surface. This is exactly what we have seen in the development of linear and cross-linked PUs using BMI as a hardener. In this work, we present a new series of the di- and tetrafuranic isocyanate-related ureas—promising curing agents for the development of polyurethanes-like self-healing materials via the Diels–Alder reaction. The commonly used isocyanates (4,4′-Methylene diphenyl diisocyanate, MDI; 2,4-Tolylene diisocyanate, TDI; and Hexamethylene diisocyanate, HDI) and furfurylamine, difurfurylamine, and furfuryl alcohol (derived from biorenewables) as furanic compounds were utilized for synthesis. The remendable polyurethane for testing was synthesized from a maleimide-terminated prepolymer and one of the T-series urea. Self-healing properties were investigated by thermal analysis. Molecular mass was determined by gel permeation chromatography. The properties of the new polymer were compared with polyurethane from a furan-terminated analog. Visual tests showed that the obtained material has thermally induced self-healing abilities. Resulting polyurethane (PU) has a rather low fusing point and thus may be used as potential material for Fused Deposition Modeling (FDM) 3D printing.

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 prepared a series of thermally remendable and recyclable polyurethanes crosslinked via reversible furan-maleimide Diels–Alder reaction based on TDI end-caped branched Voranol 3138 terminated with difurfurylamine and 4,4′-bis(maleimido)diphenylmethane (BMI). We showed that Young modulus strongly depends on BMI content (from 8 to 250 MPa) that allows us to obtain materials of different elasticity as simple as varying BMI content. The ability of DA and retro-DA reactions between furan and maleimide to reversibly bind material components was investigated by NMR spectroscopy, differential scanning calorimetry, and recycle testing. All polymers obtained demonstrated high strengths and could be recovering without significant loss in mechanical properties for at least five reprocessing cycles.

This review examines the latest advances in the synthesis and application of polyurethanes that have a self-healing effect due to the thermally reversible Diels-Alder reaction. A classification of strategies for improving the parameters of the final polymers is proposed, which includes the division into polyurethanes with a flexible organic linker, composites with nanoparticles, and systems with a dual self-healing mechanism both due to the Diels-Alder reaction and the reaction of the formation of a disulfide bonds from thiols. The possible applications of the obtained materials and the assumption about the further development of the field are considered.

Thermally-remendable and recyclable polyurethane was obtained via Diels-Alder reaction using branched glycol Voranol 3138 (glycerin-derived block-copolymer of polyethylene and polypropylene) as soft segment and toluene-2,4-diisocyanate (TDI) as hard segment subsequently functionalized by terminal difurfurylamine groups. By cross-linking via Diels-Alder reaction with N,N’-bismaleimido-4,4′-diphenylmethane (BMI) new self-healing branched polyurethane was obtained. Polymer structure was characterized by NMR and IR spectroscopy along with thermal analysis methods (DSC and TGA). Resulting material has good processability and opportunity for recycling.

ABSTRACT New monomer difurfurylamine easily obtainable from furfural (inexpensive biorenewable feedstock) was used for the synthesis of the polyurethane preform. The latest was cross‐linked with different amount of BMI (bismaleimide) via Diels–Alder reaction, and polymers with a high and low degree of cross‐linking were obtained and characterized. The self‐healing efficiency was investigated with differential scanning calorimetry, scanning electronic microscopy, X‐ray tomography, and tensile strength measurement end up to 95% restoration of mechanical properties was demonstrated for one composition after thermal treatment. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136 , 47869.

A series of N-aryl ferrocenylmethanimines was successfully lithiated at ortho-position with the following treatment with various electrophiles such as ketone, alkyl and silyl halides yielding 1,2-disubstituted ferrocenes with good yields. The product of benzophenone addition was characterized with X-ray diffraction study. We showed that cyclization of 2-hydroxymethylferrocenylcarbimines with Tf2O led to formation of 5H-pyrrolo[3,4-a]ferrocen-6-ium salt - a potential precursor of ferrocene-based heterocyclic carbenes.

Polymers containing oligoether groups, amino acid fragments, and luminophore complexes of iridium(III) in side chains are synthesized by metathesis polymerization. The photophysical properties of the compounds obtained are studied. The iridium-containing copolymers show intense green, blue-green, and red photoluminescence, and the color is determined by the nature of the iridium(III) complexes contained in polymeric emitters. Polymeric products are soluble in water and form micelles with average sizes of 19–54 nm. The cytotoxicity of the polymers with respect to A431 human epidermoid carcinoma cells is determined.

A new iridium(III) cyclometalated complex NBEpzIr(Tiq)(2) {NBEpzH is 4-[(bicyclo[2.2.1]hept-5- en-2-yl)hydroxymethylidene]-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazole-3-on and TiqH is 1-(thien-2-yl)isoquinoline} was synthesized. Copolymers with carbazole and iridium-containing fragments in side chains were obtained on the basis of the synthesized monomer by the method of ring-opening metathesis polymerization. The copolymers exhibit intense photoluminescence and electroluminescence of deep red color.

Copolymers with oligoether units and luminophoric iridium(III) complexes in the side chains have been synthesized via metathesis polymerization. The copolymers containing different luminophoric iridium(III) complexes have exhibited strong green, blue-green, or red photoluminescence. The copolymers are soluble in water, forming micelles with average size 14‒20 nm. The copolymer with red photoluminescence has low cytotoxicity with respect to epidermoid human carcinoma cells (line A431).

A new cyclometallated iridium(III) complex NBEpzIr(Piq)2 (I) (NBEpzH is 1-phenyl-3-methyl- 4-(5-bicyclo[2.2.1]hept-5-en-2-yl)-5-pyrazolone, PiqH is 1-phenylisoquinoline) is synthesized. The structure of the compound is determined by X-ray diffraction analysis (СIF file CCDC no. 1521037). Copolymers with the carbazole and iridium-containing fragments in the side chains (P1–P3) are prepared from monomer I by the ring-opening metathesis polymerization method. Their photoluminescence and electroluminescence properties are studied. Copolymers P1–P3 exhibit an intense photoluminescence and electroluminesce of red color. The maximum luminance (3010 cd/m2) and current efficiency (15.1 cd/A) are achieved for emitter P2.