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.

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 E_M 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 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.

Самовосстанавливающиеся полиуретаны на основе природного сырья Самовосстанавливающиеся полиуретаны на основе природного сырья

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.