Abstract
Traditional crosslinked diene rubber has excellent thermal–mechanical properties and solvent resistance, yet it is incapable of being recycled via universal molding or injecting. Vitrimers, a new class of covalently crosslinked polymer networks, can be topologically rearranged with the associative exchange mechanism, endowing them with thermoplasticity. Introducing the concept of vitrimers into crosslinked networks for the recycling of rubbers is currently an attractive research topic. However, designing tailored rubber vitrimers still remains a challenge. Herein, polybutadiene (PB) vitrimers with different structures were prepared via partial epoxidation of double bonds and ring-opening esterification reactions. Their mechanical and relaxation properties were investigated. It was found that the increasing crosslinking density can increase tensile strength and activation energy for altering the network topology. The influence of side-group effects on their relaxation properties shows that an increase in the number of epoxy groups on the polybutadiene chain can increase the chance of an effective exchange of disulfide units. This work provides a simple network design which can tune vitrimer properties via altering the crosslinking density and side-group effects.
Highlights
Traditional vulcanized rubbers exhibit excellent thermal stability, creep resistance, and solvent resistance due to stable three-dimensional covalently crosslinked networks
The epoxidation degree of polybutadiene could be precisely controlled by the reaction-controlled phase-transfer catalysis
Due to the network rearrangement activated by disulfide exchange, PB vitrimers exhibited substantial relaxation behavior at high temperatures, and their mechanical properties could be maintained after recycling
Summary
Traditional vulcanized rubbers exhibit excellent thermal stability, creep resistance, and solvent resistance due to stable three-dimensional covalently crosslinked networks. Xiang et al [35,36] introduced Cu2+ catalysts into sulfur vulcanized rubbers, and the activated disulfide exchange endowed them with self-healing and recycling abilities. They reported a simple strategy to prepare photo-crosslinkable polybutadiene rubbers, and disulfide exchange triggered via UV irradiation made the chemically crosslinked networks self-healable and reprocessable [16]. Cheng et al [37] introduced dithiodibenzoic acid and dithiodianiline into sulfur crosslinked epoxidized natural rubber to promote disulfide exchange, and the obtained elastomer exhibited great self-healing and recycling capabilities. A series of PB vitrimers were prepared from the ring-opening esterification reactions between epoxy groups and disulfide-containing dicarboxylic acids to study the relationship between networks and their mechanical and relaxation properties
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