Use of Diels–Alder Chemistry for Thermoreversible Cross-Linking of Rubbers: The Next Step toward Recycling of Rubber Products?

Abstract

A proof of principle for the use of Diels–Alder chemistry as a thermoreversible cross-linking tool for rubber products is demonstrated. A commercial ethylene-propylene rubber grafted with maleic anhydride has been thermoreversibly cross-linked in two steps. The pending anhydride rings were first modified with furfurylamine to graft furan groups onto the rubber backbone. These pending furans were cross-linked with a bismaleimide via a Diels–Alder coupling reaction. The newly formed Diels–Alder cross-links break at elevated temperatures (>150 °C) and can be re-formed by thermal annealing (50–70 °C). Reversibility of the rubber network was proven with infrared spectroscopy and on the basis of the mechanical properties. Furthermore, reversibility was also shown in a practical way, i.e., by cutting the used material into pieces and pressing them into new samples displaying comparable mechanical properties (impossible for conventionally cross-linked rubbers). The physical properties of the resulting products are comparable to those of conventionally cross-linked EPDM rubber and superior compared to those of their non-cross-linked precursors.

Recyclable biobased materials based on Diels–Alder cycloaddition

“…Several researchers have studied the application of the DA reaction to construct some reversible structures of linear polymers, and the kinetics of the simpler systems have been studied . In addition, a number of thermally reversible healing materials and biological materials have been constructed based on this DA reaction . Modified epoxy resin was chosen by some researchers to construct DA reversible materials .…”

Relationship among Vulcanization, Mechanical Properties and Morphology of Blends Containing Recycled EPDM

“…The ideal solution to this problem, therefore, is that the recycled material is added into the process within the industry itself, which is not so simple in the case of elastomers [4]. Elastomers like ethylene-propylene diene monomer rubber (EPDM), with unsaturations in their side groups, are less reactive and therefore more difficult to recycle [5].…”

Sustainable self‐healing elastomers with thermoreversible network derived from biomass via emulsion polymerization

“…There have been several approaches to achieve self‐healing characteristics in the polymer . Among them, the approach via DA “Click Reaction” is very important, as this is thermally reversible in nature leading to the multiple time of healing . One of the excellent examples of reversible crosslinking reaction is between a furan and a maleimide, that is, DA reaction .…”