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Polymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics. In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate‐2‐(4‐ethenylphenyl)‐5,5‐dimethyl‐1,3,2‐dioxaborinane) P(HMA‐co‐ViCL) copolymers. The ABn ${{AB}_{n}}$ ‐type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high‐performance HBV damping materials. We found that P(HMA‐co‐ViCL) 20k‐40‐60 HBV exhibited ultrahigh energy‐dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials. [ABSTRACT FROM AUTHOR]

A dense suspension of the cornstarch flowing on a very inclined wall finally forms some ridge-like patterns of the free surface. The onset of pattern formation is the primary target to elucidate the mechanism. In this work, based on the continuity of fluids and the force balance, we show that the flat free surface is unstable when the second normal stress difference N2 is negatively proportional to shear stress and the gravity component perpendicular to the wall is weak enough. Such instability is inevitable for the growth of a ridge-like surface profile oriented parallel to the flow direction. We use the instability criterion to predict the critical slope angle for the formation of ridge patterns. The estimated critical angle was found to be in agreement with experimental observations for a cornstarch suspension. [ABSTRACT FROM AUTHOR]

Abstract: Pd-B/γ-Al2O3 amorphous catalysts were prepared through impregnation and KBH4 reduction for the hydrogenation of tricyclopentadiene. The effects of reduction conditions, pre-calcination and thermal annealing on the hydrogenation activity were studied. It is found that the reduction should be conducted in ice water batch with KBH4 solution added by dropping to avoid the crystallization of amorphous metals. Pre-calcination of the catalyst before reduction can increase the amount of Pd on the prepared catalyst. With pre-calcination at 200°C, the highest hydrogenation turnover frequency is obtained. The amorphous catalyst is thermally stable at temperature below 150°C. When annealed at higher temperature, the amorphous metals are gradually crystallized and the particle size is increased. After annealing at 600°C, the catalyst is uniformly crystallized. It is noticed that the size of amorphous Pd calculated from H2-adsorption is much smaller than the actual size observed by transmission electron microscope (TEM). This indicates that amorphous metal has stronger H2-adsorption ability than crystal metals with comparative particle sizes. The hydrogenation activity decreases with the increase of annealing temperature. Moreover, the hydrogenation activity is solely dependent on the amount of H2-adsorption, suggesting that the excellent performance of amorphous catalyst should be attributed to their better H2-adsorption ability. [Copyright &y& Elsevier]

Polymers are ideally utilized as damping materials due to the high internal friction of molecular chains, enabling effective suppression of vibrations and noises in various fields. Current strategies rely on broadening the glass transition region or introducing additional relaxation components to enhance the energy dissipation capacity of polymeric damping materials. However, it remains a significant challenge to achieve high damping efficiency through structural control while maintaining dynamic characteristics.  In this work, we propose a new strategy to develop hyperbranched vitrimers (HBVs) containing dense pendant chains and loose dynamic crosslinked networks. A novel yet weak dynamic transesterification between the carboxyl and boronic acid ester was confirmed and used to prepare HBVs based on poly (hexyl methacrylate-2-(4-ethenylphenyl)-5,5-dimethyl-1,3,2-dioxaborinane) P(HMA-co-ViCL) copolymers. The ABn-type of macromonomers, the crosslinking points formed by the dynamic covalent connection via the associative exchange, and the weak yet dynamic exchange reaction are the three keys to developing high-performance HBV damping materials. We found that P(HMA-co-ViCL) 20k-40-60 HBV exhibited ultrahigh energy-dissipation performance over a broad frequency and temperature range, attributed to the synergistic effect of dense pendant chains and weak dynamic covalent crosslinks. This unique design concept will provide a general approach to developing advanced damping materials., (© 2024 Wiley‐VCH GmbH.)