Search Results (101)

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. Full article

Although dental resin composite restoratives offer a widely used direct-placement treatment option aimed at replacing the form and function of a natural tooth, there are several clinically relevant performance aspects of these materials that can be improved. The formulation of the resin matrix phase of dental composites for high-efficiency photopolymerization leading to polymers with excellent mechanical properties has always been a challenge that is addressed here through the use of structurally new and more reactive monomers as well as the formation of polymer networks that incorporate non-covalent reinforcing interactions. The purpose of this study was to validate that a set of tetraurethane diacrylates (TUDAs) with a novel configuration of their urethane linkages in coordination with acidic comonomers could be devised to obtain highly robust new composite materials. Due to the novel molecular design, this exploratory approach was conducted using reaction kinetics and three-point bend testing to assess the performance. Conversion and mechanical properties were measured to refine these formulations prior to the addition of filler. The initial formulations demonstrated outstanding dry mechanical test results that subsequently showed a major intolerance to water storage, which led to a model study using urethane diacrylate (UDA) followed by the addition of hydrophobic TUDA monomers. Once the resin formulations were optimized, silane-treated particulate filler was added to determine the effectiveness as composite materials. The final formulation used a hydrophobic, aromatic TUDA along with 4-methacryloxyethyl trimellitic anhydride (4-META) as a latent acidic comonomer and a mixture of acrylic acid (AA) and methacrylic acid (MAA). This formulation achieves a very high level of both reactivity and mechanical properties relative to current dental composite restoratives. Full article

A series of compounds with both urea and urethane moieties have been developed as color developers for high-performance thermo-sensitive paper. The compounds have lower environmental loads than conventional phenolic developers. They were also found to greatly improve the speed of the printed images. In this study, we studied the coloring mechanism of the compounds when used as developers for a fluoran dye, and we investigated the stability of the colored solid state. The urea–urethane compounds were found to form black amorphous solids with the fluoran dye. Infrared (IR) measurements of the black solids, based on six urea–urethane derivatives, revealed that the colored dye has a ring-opened structure in a carboxylic acid form and that the urea group works as a proton donor for the ring-opening reaction. The stability of the black amorphous solids was also evaluated using thermal analysis and molecular orbital calculations in addition to IR data. The results indicate that the number of urea–urethane units and the planarity of the urea moiety are important parameters for the stability of the colored solid state. Full article

Spirocalcaridines A and B are among the most challenging members of the marine invertebrate-derived Leucetta alkaloids. Approaches to the construction and elaboration of the highly compact spirocyclic core are described. The synthesis of tricyclic guanidine via tandem oxidative amination dearomatizing spirocyclization (TOADS) using hypervalent iodine set the stage for total synthesis via the migration of the C4/C8 double bond to the C4/C5 position, followed by oxidation. The undesired but not surprising propensity of the spirocyclic cyclohexadienone to undergo rearrangement to the phenol hindered the desired olefin migration. Furthermore, initial efforts to install the oxidation sequentially, first at C5 and then at C4 in the complete carbon skeleton, were fraught with unforeseen challenges and unusual outcomes. In addition, the scope and limitations of hypervalent iodine-mediated tandem oxidative dearomatizing spirocyclization on various substrates were explored. Urethanes and thiourethanes underwent spirocyclization with an excellent yield, whereas the reaction with allylic substrates and species lacking the p-methoxy substituent did not proceed. Attempts to prepare other guanidine precursors are briefly discussed. Full article

Aliphatic unsegmented polyurethanes (PUs) have garnered relatively limited attention in the literature, despite their valuable properties such as UV resistance and biocompatibility, making them suitable for biomedical applications. This study focuses on synthesizing poly(ester-urethanes) (PEUs) using 1,6-hexamethylene diisocyanate and the macrodiol α,ω-hydroxy telechelic poly(ε-caprolactone) (HOPCLOH). To optimize the synthesis, a statistical experimental design approach was employed, a methodology not commonly utilized in polymer science. The influence of reaction temperature, time, reagent concentrations, and solvent type on the resulting PEUs was investigated. Characterization techniques included FT-IR, ¹H NMR, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), optical microscopy, and mechanical testing. The results demonstrated that all factors significantly impacted the number-average molecular weight (M_n) as determined by GPC. Furthermore, the statistical design revealed crucial interaction effects between factors, such as a dependence between reaction time and temperature. For example, a fixed reaction time of 1 h, with the temperature varying from 50 °C to 61° C, did not significantly alter M_n. Better reaction conditions yielded high M_n (average: 162,000 g/mol), desirable mechanical properties (elongation at break > 1000%), low levels of unreacted HOPCLOH in the PEU films (OH/ESTER response = 0.0008), and reduced crystallinity (ΔH_m = 11 J/g) in the soft segment, as observed by DSC and optical microscopy. In contrast, suboptimal conditions resulted in low M_n, brittle materials with unmeasurable mechanical properties, high crystallinity, and significant amounts of residual HOPCLOH. The best experimental conditions were 61 °C, 0.176 molal, 8 h, and chloroform as the solvent (ε = 4.8). Full article

Electro-Fenton chemical mechanical polishing primarily regulates the generation of hydroxyl radicals (·OH) via the Fenton reaction through an applied electric field, which subsequently influences the formation and removal of the oxide layer on the workpiece surface, thereby impacting the overall polishing quality and rate. This study employs Pin–Disk friction and wear experiments to investigate the material removal behavior of single-crystal GaN during electro-Fenton chemical mechanical polishing. Utilizing a range of analytical techniques, including coefficient of friction (COF) curves, surface morphology assessments, cross-sectional analysis, and power spectral density (PSD) measurements on the workpiece surface, we examine the influence of abrasives, polishing pads, polishing pressure, and other parameters on the electro-Fenton chemical–mechanical material removal process. Furthermore, this research provides preliminary insights into the synergistic removal mechanisms associated with the electro-Fenton chemical–mechanical action in single-crystal GaN. The experimental results indicate that optimal mechanical removal occurs when using a W0.5 diamond at a concentration of 1.5 wt% combined with a urethane pad (SH-Q13K-600) under a pressure of 0.2242 MPa. Full article

In this study, we developed a novel one-pot synthesis method to fabricate well-defined single-chain polymeric nanoparticles (SCNPs) integrated with interpenetrating polymer network (IPN) systems. The synthesis process involved an initial intramolecular crosslinking of poly(methyl methacrylate-co-glycidyl methacrylate) to form SCNP followed by intermolecular crosslinking to produce single-chain nanogel (SCNG) structures. In addition, the achieved single-chain polymeric nanoparticle was subsequently incorporated into an IPN structure through urethane bond formation and a Diels–Alder click reaction involving furfuryl methacrylate (FMA) and bismaleimide (BMI). The thermal properties, swelling behaviors, and morphologies of the resulting SCNP-IPN systems were investigated. This work presents a novel strategy that integrates the single-chain folding concept with IPN systems, providing a promising platform for the development of robust and functional polymeric materials with potential applications in advanced materials science. Full article

Exploiting novel crosslinking chemistry, this study pioneers the use of waterborne polyurethane (WPU) to chemically crosslink porcine-derived gelatin, producing enhanced gelatin hydrogel films through a solvent-casting method. Our innovative approach harnesses the reactive isocyanate groups of WPU, coupling them effectively with gelatin’s hydroxyl and primary amino groups to form robust urea and urethane linkages within the hydrogel matrix. This method not only preserves the intrinsic elasticity of polyurethane but also significantly augments the films’ tensile strength and strain. Comprehensive characterizations of these hydrogel films and pre-formed hydrogel reaction mixtures were conducted using viscosity measurements, Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and the universal testing machine (UTM) for tensile-recovery assessments, alongside evaluations of their biocompatibility. The results demonstrated a reduction in pore size with an increase in WPU concentration from 2 to 6% in the developed hydrogels with a decrease in the equilibrium swelling ratio from 15% to 9%, respectively. Further, hydrogels with 6% WPU exhibited the highest tensile stress in both a dry and wet state. The gelatin hydrogel formed with 6% WPU blend also demonstrated the growth and proliferation of CCD-986K (fibroblast) and CCD-1102 (keratinocyte) cells for up to 5 days of co-culturing. The results indicate a notable enhancement in the mechanical properties and biocompatibility of gelatin hydrogels upon the introduction of WPU, positioning these films as superior candidates for biomedical applications such as tissue engineering and wound dressing. Full article

In this paper, we investigated the efficient metal-free phosphorus–nitrogen (PN) catalyst and used the PN catalyst to degrade waste PU with two-component binary mixed alcohols as the alcohol solvent. We examined the effects of reaction temperature, time, and other factors on the hydroxyl value and viscosity of the degradation products; focused on the changing rules of the hydroxyl value, viscosity, and molecular weight of polyols recovered from degradation products with different dosages of the metal-free PN catalyst; and determined the optimal experimental conditions of reaction temperature 180 °C, reaction time 3 h, and PN dosage 0.08%. The optimal experimental conditions were 180 °C, 3 h reaction time, and 0.08% PN dosage, the obtained polyol viscosity was 3716 mPa·s, the hydroxyl value was 409.2 mgKOH/g, and the number average molecular weight was 2616. The FTIR, ¹H, NMR, and other tests showed that the waste urethanes were degraded into oligomers successfully, the recycled polyether polyols were obtained, and a series of recycled polyurethanes with different substitution ratios were then prepared. A series of recycled polyurethane materials with different substitution rates were then prepared and characterized by FTIR, SEM, compression strength, and thermal conductivity tests, which showed that the recycled polyurethane foams had good physical properties such as compression strength and apparent density, and the SEM test at a 20% substitution rate showed that the recycled polyol helped to improve the structure of the blisters. Full article

Covalent adaptable networks (CANs) are polymer networks cross-linked via dynamic covalent bonds that can proceed with bond exchange reactions upon applying external stimuli. In this report, a series of cross-linked polyacrylate films were fabricated by changing the combination of acrylate monomer and the amount of diacrylate cross-linker possessing oxime–urethane bonds as a kind of dynamic covalent bond to evaluate their rheological relaxation properties. Model analysis of the experimental relaxation curves of cross-linked polyacrylate films was conducted by assuming that they consist of two types of relaxation, one of which is related to the oxime–urethane bond exchange reaction, and another of which is associated with the melting of the aggregated cross-linker. It was found that the contribution from the relaxation due to the bond exchange reaction becomes dominant only when the normal-alkyl acrylates are used as a monomer. The relaxation time was almost constant even when the amount of the cross-linker was adjusted. Moreover, it was also indicated that the miscibility of the cross-linker is very important for the fabrication of CANs with good self-healing ability and reprocessability. Full article

The mixture of hexamethylene diisocyanate (HDI) and butanol (BuOH) with the intercalation compound of 1,4-diazabicyclo[2.2.2]octane (DABCO) with α-zirconium phosphate (α-ZrP) has been evaluated as a latent thermal catalyst at varying temperatures. α-ZrP·DABCO did not show activity at 25 °C, but showed a high level of activity at a higher temperature of 80 °C. To clarify the reaction behavior of HDI-BuOH with α-ZrP·DABCO, a viscosity value of 1200 mPa·s·g/cm² was reached at 80 °C for 30 min. To investigate the deintercalation behavior of DABCO from the α-ZrP interlayer, it was investigated in BuOH and in HDI, respectively, under heated conditions. Interestingly, XRD patterns showed a reduction in α-ZrP·DABCO for the interlayer distance due to the deintercalation of DABCO in BuOH, while no changes associated with the deintercalation of DABCO were observed in HDI. Butanol was found to be important for the deintercalation of DABCO. To examine the reactivity of bifunctional monomers, the reaction of 1,4-butanediol (1,4-BDO) and HDI with α-ZrP·DABCO were investigated to show good reactivity at 80 °C and stability at 40 °C. Full article

Microwaves have been successfully employed in the Lewis acid titanium tetrachloride-assisted synthesis of peptide systems. Dipeptide systems with their amino function differently protected with urethane protecting groups have been synthesized in short periods of time and with high yields. The formation of the peptide bond between the two reacting amino acids was achieved in pyridine by using titanium tetrachloride as a condensing agent and heating the reaction mixture with a microwave reactor. The reaction conditions are compatible with amino acids featuring various side chains and different protecting groups on both the amino function and side chains. Additionally, the substrates retain their chiral integrity after reaction. Full article

Amid the rapid development of modern society, the widespread use of plastic products has led to significant environmental issues, including the accumulation of non-degradable waste and extensive consumption of non-renewable resources. Developing healable, recyclable, bio-based materials from abundant renewable resources using diverse dynamic interactions attracts increasing global attention. However, achieving a good balance between the self-healing capacity and mechanical performance, such as strength and toughness, remains challenging. In our study, we address this challenge by developing a new type of dynamic network from epoxidized soybean oil (ESO) and poly(butylene adipate-co-terephthalate) (PBAT) with good strength and toughness. For the synthetic strategy, a thiol–epoxy click reaction was conducted to functionalize ESO with thiol and hydroxyl groups. Subsequently, a curing reaction with isocyanates generated dynamic thiourethane and urethane bonds with different bonding energies in the dynamic networks to reach a trade-off between dynamic features and mechanical properties; amongst these, the thiourethane bonds with a lower bonding energy provide good dynamic features, while the urethane bonds with a higher bonding energy ensure good mechanical properties. The incorporation of flexible PBAT segments to form the rational multi-phase structure with crystalline domains further enhanced the products. A typical sample, OTSO₁₀₀-PBAT₁₀₀, exhibited a tensile strength of 33.2 MPa and an elongation at break of 1238%, demonstrating good healing capacity and desirable mechanical performance. This study provides a promising solution to contemporary environmental and energy challenges by developing materials that combine mechanical and repair properties. It addresses the specific gap of achieving a trade-off between tensile strength and elongation at break in bio-based self-healing materials, promising a wide range of applications. Full article

Aging of polymers is a natural process that occurs during their usage and storage. Predicting the lifetime of polymers is a crucial aspect that should be considered at the design stage. In this paper, a series of bio-based thermoplastic poly(ether-urethane) elastomers (bio-TPUs) with modified hard segments were synthesized and investigated to understand the structural and property changes triggered by accelerated aging. The bio-TPUs were synthesized at an equimolar ratio of reagents using the prepolymer method with the use of bio-based poly(trimethylene ether) glycol, bio-based 1,3-propanediol, and hexamethylene diisocyanate or hexamethylene diisocyanate/partially bio-based diisocyanate mixtures. The polymerization reaction was catalyzed by dibutyltin dilaurate (DBTDL). The structural and property changes after accelerated aging under thermal and hydrothermal conditions were determined using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical thermal analysis (DMTA). Among other findings, it was observed that both the reference and aged bio-TPUs decomposed in two main stages and exhibited thermal stability up to approximately 300 °C. Based on the research conducted, it was found that accelerated aging impacts the supramolecular structure of TPUs. Full article

High-energy-density Li-CO₂ batteries are promising candidates for large-capacity energy storage systems. However, the development of Li-CO₂ batteries has been hindered by low cycle life and high overpotential. In this study, we propose a CO₂-based thermoplastic polyurethane (CO₂-based TPU) with CO₂ adsorption properties and excellent self-healing performance to replace traditional polyvinylidene fluoride (PVDF) as the cathode binder. The CO₂-based TPU enhances the interfacial concentration of CO₂ at the cathode/electrolyte interfaces, effectively increasing the discharge voltage and lowering the charge voltage of Li-CO₂ batteries. Moreover, the CO₂ fixed by urethane groups (-NH-COO-) in the CO₂-based TPU are difficult to shuttle to and corrode the Li anode, minimizing CO₂ side reactions with lithium metal and improving the cycling performance of Li-CO₂ batteries. In this work, Li-CO₂ batteries with CO₂-based TPU as the multifunctional binders exhibit stable cycling performance for 52 cycles at a current density of 0.2 A g⁻¹, with a distinctly lower polarization voltage than PVDF bound Li-CO₂ batteries. Full article