Thermoreversible cross-linking of ethylene/propylene copolymer rubbers

Abstract

This study demonstrates an efficient method for the synthesis of thermoreversible cross-linked ethylene/propylene rubbers (EPRs) via two steps; in the first step, a functional olefin monomer containing a furan group (FO) is designed and the ethylene/propylene/FO terpolymerization catalyzed by a traditional Ziegler–Natta catalyst is implemented; in the second step, a cross-linked network is constructed via Diels–Alder (DA) click reaction between the bismaleimide and pendant furan groups in the EPR chains. Via polymerization, the FO content in the copolymers was tailored in relatively wide range from 1.1 mol% to 9.7 mol%; this provided various cross-linking precursory groups for the DA reaction. Moreover, the cross-linking density could be adjusted via not only the amount of the inserted furan group but also the ratio of furan to bismaleimide. These solid thermoreversibile EP rubbers could perform their de-cross-linking above 110 °C and re-form the network below 85 °C in a heating–cooling cycle not only in the static measurement of FTIR, but also in the dynamic test of DMA. The mechanical properties of the resulting products with varied cross-linking densities were compared with that of the non-cross-linked polymer and proved to be of much higher modulus. This thermoreversible cross-linking behavior also provided a new strategy for local-repairing of any crack in rubber products.