Recyclable Sulfur-Cured Rubbers with Enhanced Creep Resistance and Retained Mechanical Properties by Terminal Metal Coordination

Abstract

The construction of dynamic covalent polymer networks (DCPNs) is an effective way to achieve the recycling of vulcanized rubbers. However, rubbers with DCPNs were susceptible to creep, causing poor dimensional stability which limits their applications. Sulfur vulcanization is the most widely used crosslinking technology in the rubber industry owing to its excellent comprehensive performance. It is of great importance to achieve the recyclability of sulfur-cured rubbers with improved creep resistance. Herein, the recyclable sulfur-cured polyisoprene rubber network was prepared by introducing a catalyst copper ion (Cu2+) to catalyze the disulfide metathesis reaction of inherent disulfide and polysulfide bonds. Then, the terminal hydroxyl and pyridyl groups were introduced into the polyisoprene chain to reduce the catalytic activity of Cu2+ at service temperature by coordinate interactions, thus improving the creep resistance. The resulting networks exhibited superior creep resistance even at a service temperature of 100 °C, although they had lower topology freezing transition temperatures (T vs), while the corresponding network rearrangement ability at elevated temperatures was not affected. Moreover, the recycled samples displayed excellent mechanical properties with tensile strengths exceeding 7 MPa and the elongation at break over 600%, which were significantly higher than those of most reported polydiene rubber systems with DCPNs in the literature. This work provides a strategy for designing recycled rubbers with enhanced creep resistance, sufficient tensile strength, and superior stretchability using industrial sulfur-vulcanized processes.

Creep resistance in doubly crosslinked dynamic covalent networks

“…For example, Xu et al reported that disulfide-cured hydroxyl and pyridyl functionalized polyisoprene block copolymers exhibited excellent creep resistance in the presence of Cu 2+ ions through cationic coordination within the network. 38 Zhu and coworkers demonstrated that incorporating transition metal catalysts in polyimine vitrimers led to creep suppression due to metal-ligand coordination. 39 Physical crosslinking by hydrogen bonds has also been utilized to enhance the properties of networks.…”