Dynamic bonds are usually used to endow thermoset materials with excellent reprocessability. Nevertheless, this strategy sacrifices the thermal stability in most instances. In recent years, the dynamic silyl ether (Si O R) has attracted great attention due to its excellent thermal stability. However, the reprocessability of thermoset materials based on it is far from satisfactory because of the inactive dynamic exchange reaction. Herein, a species of activated silyl ether with neighboring groups is identified via small-molecule model reaction and the corresponding activation energy is calculated by reaction kinetics for the first time. Based on the activated silyl ether linkages, the poly(dimethylsiloxane) elastomers with high mechanical strength, effective reprocessability, and thermal stability are further designed and prepared. In a word, this work fills a research gap about the effect of neighboring groups on the dynamic characteristic of silyl ether and provides a theoretical basis for the construction of activated silyl ether linkages, endowing the materials with thermal stability and efficient reprocessability.
Yinqiao Liu,Jialu Han,Wensheng Yan,Qiuran Jiang,Jiamei Luo,Liying Zhang,Jun Wang,Wanshuang Liu
Growing environmental concerns are driving the development of bio-based and recyclable thermosetting polymers. In this work, we synthesized a novel liquid cycloaliphatic epoxide containing silyl ether bonds from α-terpineol, a renewable monoterpene alcohol. After optimizing the accelerator content, the epoxy resin cured with methylhexahydrophthalic anhydride exhibited a high glass transition temperature (172 °C) and an acceptable tensile strength (57.2 MPa), the presence of silyl ether bonds imparts the resin with inherent degradability in fluoride and acidic organic solutions, offering a pathway for recycling. Finally, the optimized epoxy system was used to prepare a thermally conductive adhesive with boron nitride (BN) as the filler. The resulting epoxy composite 35 wt% BN, exhibited an enhanced thermal conductivity of 1.298 W/m·K. Crucially, the high-value BN fillers could be recovered non-destructively through selective chemical recycling of the epoxy matrix.
In recent years, as an emerging dynamic bonding, silyl ether linkages have been concerned and applied. However, the reprocessability of vitrimers based on it is far from satisfactory because of the inactive dynamic exchange reaction. At the same time, the mechanical properties of polysiloxane elastomers are poor because of the high flexibility of polysiloxane molecular chains and weak intermolecular forces. Herein, we have successfully synthesized a PDMS elastomer incorporating Zn(II)-amine coordination bonds as sacrificial units, which are crosslinked through dynamic silyl ether linkages. Importantly, the presence of Zn ions promotes the exchange between the silyl ether linkages and hydroxyl groups. The elastomers exhibited excellent mechanical properties (35 times improvement in toughness) and outstanding reprocessability. The mechanical property recovery of the PDMS elastomers reached approximately 90% after four reprocessing cycles. Meanwhile, small-molecule simulation experiments were conducted to verify the significant catalytic effect of Zn (II) ions as Lewis acid catalysts on the exchange reaction of silyl ether linkages and hydroxyl groups. In a word, this work provides a facile strategy to simultaneously enhance the mechanical properties and reprocessing performance of silyl ether-linked polysiloxane elastomers. Graphical
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