The effect of epoxidation on strain‐induced crystallization (SIC) of epoxidized natural rubber (ENR) and mechanism are studied with synchrotron radiation wide‐angle X‐ray diffraction (SR‐WAXD) and polarized infrared spectroscopy (P‐IR). WAXD results reveal that appropriate epoxidation, for example, ENR‐25 epoxidized with ≈25% isoprene units, can unexpectedly enhance the SIC of natural rubber (NR), resulting in the improvement of tear resistance. On the other hand, exorbitant epoxidation, for example, ENR‐40 epoxidized with ≈40% isoprene units, depresses the SIC and weakens the mechanical properties of NR remarkably. P‐IR studies reveal that epoxidation can promote the orientation of chain segments along the stretching direction, which plays a determining role on SIC of NR. Accordingly, hierarchical multiscale schematic models are proposed. This insight into epoxidation on SIC of ENR strongly suggests that ENR with appropriate epoxidation degree is a promising candidate material for the fabrication of high‐performance engineering rubber products.
The
bio-based epoxidized natural rubber (ENR) is considered
a promising
platform to design and fabricate sustainable and high-performance
rubber materials. The epoxide sites in the ENR chains contribute to
designing a green cross-linking strategy to reduce the release of
toxic volatile organic compounds and achieve the recycling of end-of-life
rubbers. However, it is still challenging to achieve a catalyst-free
and effective cross-linking strategy and obtain a cross-linked ENR
with mechanically robust properties. Herein, a series of carboxylic
acids with different chain lengths and degrees of functionality were
synthesized through the catalyst-free and solvent-free alcoholysis
of maleic anhydride and served as cross-linkers for ENR. We demonstrated
that the increased chain lengths and degrees of functionality of carboxylic
acids were conducive to increasing the rate and efficiency of the
epoxy–acid cross-linking reaction and improving the mechanical
properties of ENR compared with those of commercial maleic acid. Hence,
ENR could be facilely and effectively cross-linked by the modified
carboxylic acids without additional additives, producing β-hydroxy
ester linkages. The mechanical properties of ENR/carbon black composites
could be facilely adjusted via changing the structure and content
of the cross-linkers. Due to the introduction of the exchangeable
β-hydroxy ester linkages, the covalently cross-linked networks
could be able to achieve topological rearrangements via transesterifications,
thus conferring the cross-linked ENR with good reprocessability. Moreover,
the carboxylic acid-cured ENR showed the improved thermal-oxidative
aging resistance compared to sulfur-curd one because the formed ester
cross-links are thermally stable. This work provides a catalyst-free,
efficient and green cross-linking strategy for the epoxidized elastomer,
which could open a broad application scenario in vitrimer-like rubbers.
Tire development tendency is green, environment-friendly, and safeguarding life and health. The conventional tires, consisting of solution polymerized styrene-butadiene rubbers (SSBR), silica, silane coupling agents, and other rubber additives, will not be able to keep up with the demand. SSBR, as a synthetic rubber processed from nonrenewable petroleum resources, creates a large amount of carbon emissions in the production process and the reaction between silica and silane coupling agents generates a large amount of volatile organic compounds (VOCs), which is detrimental to the environment and human health. In this article, epoxidized natural rubber (ENR) with different epoxide degrees was successfully prepared and blended with natural rubber (NR)/silica composites to improve the dispersion of silica and the performance of nanocomposites. The effect of heat treatment temperature on the reaction between ENR and silica and the dynamic and static mechanical properties of ENR/NR/silica nanocomposites was investigated by mechanical properties test, transmission electron microscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared. The results showed that the epoxy groups on the ENR molecular chain could react with the silanol on the surface of silica to form a strong chemical bond, which improved the dispersion of silica in the rubber matrix and further enhanced the performance of the rubber composites without carbon emission and VOCs.
The DNA-encoded library (DEL) is a powerful hitgeneration tool in drug discovery. This study describes a new DEL with a privileged scaffold quinazolin-4(3H)-one developed by a robust DNA-compatible multicomponent reaction and a series of novel glutathione S-transferase (GST) inhibitors that were identified through affinity-mediated DEL selection. A novel inhibitor 16 was subsequently verified with an inhibitory potency value of 1.55 ± 0.02 μM against SjGST and 2.02 ± 0.20 μM against hGSTM2. Further optimization was carried out via various structure−activity relationship studies. And especially, the cocrystal structure of the compound 16 with the SjGST was unveiled, which clearly demonstrated its binding mode was quite different from the known GSH-like compounds. This new type of probe is likely to play a different role compared with the GSH, which may provide new opportunities to discover more potent GST inhibitors.
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