A Structure-Properties Relationship Study of Self-Healing Materials Based on Styrene and Furfuryl Methacrylate Cross-Linked via Diels–Alder Chemistry

A series of copolymers of styrene and furfuryl methacrylate characterized by various molecular structures (linear and star, block and random) is synthesized via atom transfer radical polymerization, and cross-linked with a bismaleimide by means of thermally reversible Diels–Alder (DA) reaction, to obtain self-healing materials. The prepared materials are studied in terms of gelation, swelling, thermal, and dynamic-mechanical analysis, with the aim of correlating relevant properties to their chemical structure. It is found that the furan/styrene ratio, as well as the molecular architecture, have a major influence on the properties. It is also found that the reversibility of the DA reaction is not complete in the solid state for materials with high cross-linking density. This study provides some important tools for the design of materials characterized by thermally reversible behavior, which find usually application as self-healing thermosets, coatings, or adhesives.     

Dual-Responsive Self-Healable Carboxylated Acrylonitrile Butadiene Rubber Based on Dynamic Diels–Alder “Click Chemistry” and Disulfide Metathesis Reaction

Introduction of the self-healing property in the commercially available elastomers promotes the development of high-end elastomeric products with an extended lifespan. Herein, a smart functionalized carboxylated nitrile rubber (XNBR) is prepared based on dynamic phototriggered disulfide metathesis and thermoreversible Diels–Alder (DA) “click chemistry.” In this case, the XNBR is functionalized with furfuryl amine (FA) followed by crosslinking with a dual functional crosslinker having a maleimide as well as a disulfide functionality for participating in the DA reaction and to induce the UV-triggered disulfide metathesis reaction, respectively. The self-healing properties are studied by thermal, mechanical, and microscopy analyses. The crosslinked materials present an impressive self-healing efficiency of ≈88% and a tensile strength of ≈10 MPa without affecting its oil-resistance property whereas pristine XNBR and furfuryl-functionalized XNBR (FXNBR) show tensile strengths only 0.4 and 0.6 MPa, respectively. Furthermore, the crosslinked rubber is demonstrated to be recyclable, without much loss of its mechanical properties. In a nutshell, the use of this smart dual pathway of self-healing can pave a new direction in sustainable development in NBR elastomers.     

Self-Healable Hydrophobic Material Based on Anthracenyl Functionalized Fluorous Block Copolymers via Reversible Addition-Fragmentation Chain Transfer Polymerization and Rapid Diels–Alder Reaction

Recently, among the available approaches to develop self-healable materials, 1,2,4-triazoline-3,5-dione (TAD)-based Diels–Alder (DA) chemistry has gained tremendous attention, becuase this DA reaction is very rapid under ambient conditions. This study delineates developing a self-healing hydrophobic fluorinated polymer utilizing dynamic and rapid TAD-DA chemistry. For this purpose, block copolymers of 2-hydroxyethyl methacrylate (HEMA) and 2,2,2-trifluoroethylmethacrylate (TFEMA) are prepared via reversible addition-fragmentation chain transfer polymerization. Subsequently, the pendant hydroxyl groups of the HEMA repeat units are modified with anthracenyl functionality via esterification with 9-anthracenecarboxylic acid. The tailor-made polymer-bearing anthracenyl pendants are subsequently crosslinked via a rapid DA reaction using a bifunctional TAD derivative at room temperature (r.t.). Differential scanning calorimetry (DSC) analysis is performed to interpret the thermoreversible behavior of the TAD-derived DA polymer. The self-healing characteristics of this TAD-derived DA conjugate are studied by monitoring the healing of a notched surface via AFM analysis. Interestingly, the TAD conjugated fluoropolymers are hydrophobic, as evidenced by the water contact angle analysis. Such TAD-derived DA fluoropolymer conjugates with remarkable hydrophobic characteristics and excellent self-healing features can pave a new direction in the potential materials for specialty paints, coatings, and adhesives.     

Protein Modification via Nitrile Oxide−Dehydroalanine Cycloaddition: Formation of Isoxazoline Ring on the Protein Backbone

Here we describe a novel catalyst-free 1,3-dipolar cycloaddition bioconjugation approach for chemical modification of proteins. The dehydroalanine (Dha)-containing protein reacts with nitrile oxides generated in situ through 1,3-dipolar cycloaddition in fully aqueous-buffered systems. This leads to the formation of a new isoxazoline ring at a pre-defined site (Dha) of the protein. Furthermore, the 1-pyrene isoxazoline-installed annexin V acts as a fluorescent probe, which successfully labels the outer cellular membranes of human cholangiocarcinoma (HuCCA-1) cells for detection of apoptosis.     

Effect of Magnesium Oxide and the Testing Rate on the Viscosity and Adhesion Properties of Epoxidized Natural Rubber/Acrylonitrile–Butadiene Rubber Blend Based Adhesives

The effect of magnesium oxide loading on the adhesion properties of epoxidized natural rubber (ENR 50)/acrylonitrile–butadiene rubber (NBR)-based pressure-sensitive adhesives was systematically investigated using 40 parts per hundred parts of rubber (phr) of coumarone–indene resin as the tackifier. The concentration range of magnesium oxide was from 10–50 phr. Toluene and polyethylene terephthalate (PET) films were selected as the solvent and the substrate, respectively, throughout the experiment. A Sheen hand coater was used to coat the adhesive onto the PET substrate at various coating thicknesses. The viscosity of the adhesive was measured using a Brookfield viscometer, whereas the loop tack, peel strength, and shear strength were determined using an adhesion tester operating at 10–60 cm/min. The results indicate that the viscosity increases with magnesium oxide loading, an observation which is attributed to the concentration effect of the filler. However, loop tack, peel strength, and shear strength increase with magnesium oxide loading up to 30 phr before decreasing upon further addition of the filler. This observation is ascribed to the effect of a varying degree of wettability of the adhesive, which culminates at 30 phr of magnesium oxide loading. At a fixed loading of magnesium oxide, all the adhesion properties of adhesives increase upon increasing the coating thickness and rate of testing.     

Dependences of the Oxygen Reduction Reaction Activity of Pd–Co/C and Pd–Ni/C Alloy Electrocatalysts on the Nanoparticle Size and Lattice Constant

Carbon-supported Pd-based binary alloy electrocatalysts (Pd–Co and Pd–Ni) with different particle sizes for polymer electrolyte fuel cells were prepared by a NaBH₄ reduction method and investigated to examine effects of the size and lattice constant of the Pd alloy nanoparticles on the oxygen reduction reaction (ORR) activity. The particle size and lattice constant were controlled in the wide ranges 4.2–12.1 and 0.3802–0.3948 nm, respectively by heating the catalysts in specific atmospheres. The alloy structures were characterized by X-ray diffraction, transmission electron microscopy and X-ray absorption fine structure. The electrochemical tests of the Pd–Co/C and Pd–Ni/C catalysts were performed by cyclic voltammetry and rotating disk electrode in 0.1 M HClO₄. Nearly linear relationship between the lattice constant and nanoparticle size was observed with the Pd–Co and Pd–Ni nanoparticles. The nanoparticle sizes and lattice constants of the Pd–Co/C and Pd–Ni/C electrocatalysts, which influence the Pd d-band center, showed positive and inverse relations with the ORR specific activities, respectively. The mass activities of the Pd–Co/C and Pd–Ni/C electrocatalysts showed an increasing trend with the lattice expansion.     

Generation of protonic acid sites from pentane on the surfaces of Pt/SO42−-ZrO2 and Zn/H-ZSM5 evidenced by IR study of adsorbed pyridine

Pyridinium ion was formed from pyridine, which had been bound to Lewis acid sites on Pt/SO₄^2?-ZrO₂ and Zn/H-ZSM5 by contact with pentane vapor. Protonic acid sites were generated on these surfaces by contact with pentane. The protonic acid sites generated in the presence of pentane were eliminated when pentane was removed from gas phase. The generation of the protonic acid sites occurred above 350 K for Pt/SO₄^2?-ZrO₂ and above room temperature for Zn/H-ZSM5.     

Effects of microstructure on the microwave dielectric properties of Ba(Co1/3Nb2/3)O3 and (1−x)Ba(Co1/3Nb2/3)O3–xBa(Zn1/3Nb2/3)O3 ceramics

Ba(Co_1/3Nb_2/3)O₃(BCN) has a 1:2 ordered hexagonal structure. A large amount of the liquid phase, which contains high concentrations of Ba and Nb ions was found in the BCN ceramics. Q-values of BCN increased with increasing sintering temperature; however, it significantly decreased when the sintering temperature exceeded 1400 °C. The presence of a large amount of liquid phase could be responsible for the decrease of the Q-value. For (1−x)Ba(Co_1/3Nb_2/3)O₃–xBa(Zn_1/3Nb_2/3)O₃ [(1−x)BCN–xBZN] ceramics, the 1:2 ordered hexagonal structure was observed in the specimens with x⩽0.3 and the BaNb₆O₁₆ second phase was found in the specimens with x⩾0.6. Grain growth, which is related to the BaNb₆O₁₆ second phase occurred in the specimens with x⩾0.5. In this work, the excellent microwave dielectric properties of τ_f=0.0 ppm/°C, ε_r=34.5 and Q×f=97,000 GHz were obtained for the 0.7BCN–0.3BZN ceramics sintered at 1400 °C for 20 h.