Supramolecularly toughened and elastic epoxy resins by grafting 2-ureido-4[1H]-pyrimidone moieties on the side chain

Intrinsic Self-Healable, Corrosion-Resistant Silicone Coating Based on Quadruple Hydrogen-Bonded Supramolecular Polymer

Corrosion-resistant coatings with self-healing capabilities are still a great challenge for metal protection. In this study, a corrosion-resistant coating with intrinsic self-healing capabilities was developed by compounding hydroxy-terminated silicone oil (HTSO) with 2-ureido-4[1H]-pyrimidone (UPy) derivatives. The smooth surface of the coating was shown by scanning electron microscopy (SEM), and good smoothness was also exhibited in the cross-section, which indicated that the coating is very homogeneous from the top to the bottom. Thermogravimetric analysis (TG) was employed to illustrate the temperature-resistant characteristics of the coating, revealing its significant chemical stability up to 360 °C. The corrosion resistance of the coating is assessed through electrochemical impedance spectroscopy (EIS), the typical impedance at 0.01 Hz is 1.70 × 109 and 2.44 × 108 Ω·cm2 before and after exposure to a 3.5 wt % NaCl solution for 70 days. There was no significant change in the water contact angle of the coatings before and after immersion; however, the adhesion strength was reduced. Notably, the coating demonstrates immediate and multiple self-healing properties. The tensile stress of the associated healing sample experiences an augmentation within the temperature range of 30-120 °C, with the critical fracture strain of the healed sample reaching 235% at 120 °C. The self-healing mechanism of the coating is systematically investigated using in situ Raman spectroscopy.

Verification of the Self-Healing Ability of PP-co-HUPy Copolymers in Epoxy Systems

This work concerns the verification of the self-healing ability of PP-co-HUPy copolymers dispersed in epoxy systems. PP is the acronym for the Poly-PEGMA polymer, and HUPy refers to the HEMA-UPy copolymers based on ureidopyrimidinone (UPy) moieties. In particular, this work aims to verify whether this elastomer characterized by an intrinsic self-healing ability can activate supramolecular interactions among polymer chains of an epoxy resin, as in the elastomer alone. The elastomer includes a class of polyethylene glycol monomethyl ether methacrylate-based copolymers, with different percentages of urea-N-2-amino-4-hydroxy-6-methyl pyrimidine-N'-(hexamethylene-n-carboxyethyl methacrylate) (HEMA-UPy) co-monomers. The self-healing capability of these copolymers based on possible quadruple hydrogen bond interactions between polymer chains has been verified. The formulated epoxy samples did not show self-healing efficiency. This can be attributed to the formation of phase segregation that originates during the curing process of the samples, although the PP-co-HUPy copolymers are completely soluble in the liquid epoxy matrix EP. The morphological investigation highlighted the presence of crystals of PP-co-HUPy copolymers, which are in greater quantity in the sample containing the highest weight percentage (7.8 wt%) of HUPy units. Furthermore, the crystals act as promotors for increasing the curing degree (DC) of the epoxy systems containing HUPy units. DC goes from 91.6% for EP to 96.1% and 95.4% for the samples containing weight percentages of 2.5 and 7.8 wt% of HUPy units, respectively. Dynamic mechanical analysis (DMA) shows storage modulus values for epoxy systems containing PP-co-HUPy units lower than that of the unfilled resin EP. The values of maximum in Tan δ (Tg), representing the temperature at which the glass transition occurs, are 220 for the unfilled resin EP, 228 for the sample containing 2.5 wt% of HEMA-UPy units, and 211 for the sample containing 7.8 wt% of HEMA-UPy units.

Phase separation in supramolecular and covalent adaptable networks

Phase separation phenomena have been studied widely in the field of polymer science, and were recently also reported for dynamic polymer networks (DPNs). The mechanisms of phase separation in dynamic polymer networks are of particular interest as the reversible nature of the network can participate in the structuring of the micro- and macroscale domains. In this review, we highlight the underlying mechanisms of phase separation in dynamic polymer networks, distinguishing between supramolecular polymer networks and covalent adaptable networks (CANs). Also, we address the synergistic effects between phase separation and reversible bond exchange. We furthermore discuss the effects of phase separation on the material properties, and how this knowledge can be used to enhance and tune material properties.

CaCO3 Crystals with Unique Morphologies Controlled by the Hydrogen-Bonded Supramolecular Assemblies of Ureido-Pyrimidinone-Amino Acid Derivatives

Biomineral materials such as nacre of shells exhibit high mechanical strength and toughness on account of their unique "brick-mortar" multilayer structure. 2-Ureido-4[1H]-pyrimidinone (UPy) derivatives with different types of end groups, due to the self-complementary quadruple hydrogen bonds and abundant Ca²⁺ binding sites, can easily self-assemble into supramolecular aggregates and act as templates and skeleton in the process of inducing mineral crystallization. In this work, UPy derivatives were used as templates to induce the mineralization and growth of CaCO₃ through a CO₂ diffusion method. The morphology of CaCO₃ crystals was modulated and analyzed by adjusting the synthesizing parameters including Ca²⁺ concentration, pH, and end groups. The results showed that, by the regulatory role of the mineralization template, it was easier to realize the multilayer crystal structure at a lower concentration of Ca²⁺ (less than 0.01 mol L^-1). Under alkaline regulation, the quadruple hydrogen bonds would be destroyed, and the template's regulation effect on the morphology of CaCO₃ crystals would be weakened. Moreover, by comparing different types of end groups, it was proven that the UPy derivatives with carboxylic acid groups (-COOH) played a crucial role in the process of CaCO₃ crystallization with unique morphologies.

Improving the Intrinsic Stretchability of Fully Conjugated Polymer for Deep-Blue Polymer Light-Emitting Diodes with a Narrow Band Emission: Benefits of Self-Toughness Effect

It is challenging to construct the intrinsically stretchable active layer of rigid conjugated polymers (CPs) toward flexible deep-blue light-emitting diodes (FLEDs). Inspired by the self-toughness effect, sacrificial hydrogen bonding (H-bonding) and a cross-linked network synergistically enabled polydiarylfluorene (PFs-NH) films to present efficient deep-blue emission and excellent intrinsic stretchability. In particular, a cross-linked network structure presenting viscoelasticity behaviors, which was successfully inherited into postprocessed films with interchain interpenetration and a crystallinity domain and behaved as energy absorption and dissipation centers, was induced by the interchain H-bonding interaction in toluene (Tol) precursor solutions where the storage moduli (G') gradually exceeded the loss moduli (G″). Subsequently, intrinsic stretchable films with a tensile rate of 30% were prepared from Tol solutions, different from the brittle films from polar solvents. Eventually, narrow band, deep-blue PLEDs showed a maximum EQE of 1.28% and a full width half-maximum (fwhm) of 28 nm. Therefore, the self-toughness effect induced by hierarchical structures will be feasible to obtain high-performance FLEDs.

Preparation of basalt fibers grafted with amine terminated urea-based oligomer and its application in reinforcing conventional glass ionomer cement

The purpose of this study was to improve interfacial interaction between basalt fibers (BF) and glass ionomer cement (GIC) matrix with grafting amine terminated urea-based oligomer (DIEDA) onto the surface of BF. The DIEDA-BF was prepared by the reaction between 3-aminopropyl- triethoxysilane (APS) modified BF with Isophorone diisocyanate (IPDI) and followed with ethylenediamine (EDA). The reaction was repeated to obtain three generations of DIEDA-BF which were marked as DIEDA-BF-G₁, DIEDA-BF-G₂, and DIEDA-BF-G₃, respectively. X-ray photoelectron spectroscopy (XPS) was used to characterize DIEDA-BF. 3D morphology analysis was taken to investigate the variation of BF after being treated with EDA. Three-point bending-test, compressive strength (CS) test, and fracture toughness (FT) were used to evaluate the reinforcement effect of DIEDA-BF on commercial GIC (GC Fuji IX). Water sorption (WS) and solubility (SL) were measured according to the mass variation at fixed time intervals. The changes of flexural strength (FS) and modulus (FM) after water immersion were used to evaluate the water-aging resistance of DIEDA-BF reinforced GIC. Pure GIC and APS reinforced GIC (APS-GIC) were used as double control groups. The XPS analysis indicated that DIEDA was successfully grafted onto the surface of BF. 3D morphology analysis revealed that BF could be corroded in EDA, thus DIEDA-BF-G₃ had lower N content on the surface than DIEDA-BF-G₂. The results of mechanical tests showed that DIEDA-BF-G₁ and DIEDA-BF-G₂ had the best reinforcement effect. The DIEDA-BF-G₁ reinforcement GIC (DIEDA-BF-G₁-GIC) was chosen for WS, SL, and water aging resistance test further. The results showed that all fiber reinforced GICs had higher WS than pure GIC, and the relationship in SL between fiber reinforced GICs and pure GIC varied with immersion time. The FS of DIEDA-BF-G₁-GIC decreased after one week of water immersion, and had no variation after prolonging the immersion time. After three months of water immersion, DIEDA-BF-G₁-GIC still had much higher FS than pure GIC and APS-BF-GIC. DIEDA could improve the interfacial interaction between BF and GIC matrix. After long term of water immersion, DIEDA-BF reinforced GIC still had FS higher than 50 MPa, which even met the ISO requirement in FS for dental resin composite. Therefore, GIC/DIEDA modified BF composite had potential to be used in stress bearing areas in dentistry.

Force-Induced Self-Assembly of Supramolecular Modified Mica Nanosheets for Ductile and Heat-Resistant Mica Papers

Mica is a naturally abundant layered silicate mineral that has higher strength than other layered silicate minerals, but its inherent brittleness limits its application in some fields. In this work, mica was ultrasonically exfoliated into a single-layered nanomaterial after thermal activation, acidification, sodium replacement, and cetyltrimethylammonium bromide (CTAB) intercalation and then modified with ureido-pyrimidinone (UPy)-based PEG chains. Vacuum-assisted self-assembly was used to construct supramolecularly modified single-layered mica into bulk materials, in which the mica nanosheets were stacked into mica paper. The reversible quadruple hydrogen-bonded UPy moieties provided a high binding constant and significantly improved the strength and toughness of the obtained mica paper. These force-induced assembled mica papers showed significantly improved tensile strength and toughness compared with pure mica paper and simultaneously maintained the heat resistance of the mica materials, which may be good candidates for the substrates of flexible sensors working at higher temperatures.

Thermal properties of polybenzoxazine exhibiting improved toughness: Blending with cyclodextrin and its derivatives

Polybenzoxazines are emerging as a class of high-performance thermoset polymers that can find their applications in various fields. However, its practical application is limited by its low toughness. The cyclic β-cyclodextrin and a newly synthesized derivative (β-cyclodextrin-MAH) were separately blended with benzoxazine to improve the toughness of polybenzoxazine. The results revealed that the maximum impact strength of the blend was 12.24 kJ·m−2 and 14.29 kJ·m−2 when 1 wt.% of β-Cyclodextrin and β-Cyclodextrin-MAH, respectively, were used. The strengths were 53% and 86% higher than that of pure polybenzoxazine. The curing reaction, possible chemical structures, and fractured surface were examined using differential scanning calorimetry, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques to understand the mechanism of generation of toughness. The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and β-cyclodextrin and β-cyclodextrin-MAH resulted in the generation of toughness. Furthermore, the curves generated during thermogravimetric analysis did not significantly change, revealing the good thermal properties of the system. The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties. This can be a potential way of modifying the thermoset resins.

Rapid Preparation of MWCNTs/Epoxy Resin Nanocomposites by Photoinduced Frontal Polymerization

Due to their excellent mechanical and thermal properties and medium resistance, epoxy/carbon nanotubes and nanocomposites have been widely used in many fields. However, the conventional thermosetting process is not only time- and energy-consuming, but also causes the agglomeration of nanofillers, which leads to unsatisfactory properties of the obtained composites. In this study, multi-walled carbon nanotubes (MWCNTs)/epoxy nanocomposites were prepared using UV photoinduced frontal polymerization (PIFP) in a rapid fashion. The addition of MWCNTs modified by a surface carboxylation reaction was found to enhance the impact strength and heat resistance of the epoxy matrix effectively. The experimental results indicate that with 0.4 wt % loading of modified MWCNTs, increases of 462.23% in the impact strength and 57.3 °C in the glass transition temperature Tg were achieved. A high-performance nanocomposite was prepared in only a few minutes using the PIFP approach. Considering its fast, energy-saving, and environmentally friendly production, the PIFP approach displays considerable potential in the field of the fast preparation, repair, and deep curing of nanocomposites and coatings.

Developing an epoxy resin with high toughness for grouting material via co-polymerization method

In order to improve the toughness of epoxy resin for grouting material, the flexible hexamethylene diisocyanate (HDI) was utilized to manufacture a new kind of epoxy resin with high toughness via co-polymerization method. In the procedure of preparing bisphenol A epoxy resin, before the reaction between bisphenol A (BPA) and epichlorohydrin (ECH), HDI was introduced to react with BPA for embedding flexible segments into the chain of epoxy resin, then modified epoxy resin (HDI/EP) was manufactured. The mechanical properties, especially the toughness of the HDI/EP, are significantly increased – the fracture elongation is up to 124%. In addition, the compressed specimens can fully recover to their original shape in a few minutes. Thermal performance and corrosion resistance of the HDI/EP specimen were also investigated, which showed that the specimen can be used under 258°C, and can remain stable in H2SO4, NaOH and NaCl solutions with 10 wt% for 100 h, respectively. The present work provides a convenient avenue pathway to prepare an epoxy resin with high toughness, which may be used in many technologies.

A ureido-pyrimidone based aspartic acid derivative: synthesis and pH-responsive self-assembly in water

The pH-responsive UPy-aspartic acid aggregates can act as templates for the controlled synthesis of silver nanostructures.