Two-Step Chemical Recycling of Tire Rubber to Isoprene

The development of chemical recycling methods for waste polymers and the production of easily recyclable polymers have become important trends in chemical research. Here, we report a two-step chemical recycling method for tire rubber. This method involves cyclodepolymerization (CDP) through the successive ring-closing metathesis of isoprene rubber (reinforced by sulfur cross-linking and a carbon black (CB) filler) and pyrolytic process of the oligomer/polymer into monomeric isoprene. The metathetic process efficiently solubilized the organic components of the tire-like rubber, allowing them to be easily separated from CB without heating. The resulting organic phase consisted of a high-purity isoprene oligomer/polymer (Mn = 1000 Da) whose main product of the cyclodepolymerization was an isoprene cyclic tetramer with cis-, cis-, cis-, and trans-configurations. The pyrolytic fragmentation of the isoprene oligomer/polymer provided the isoprene monomer as the main product along with valuable chemicals such as benzene/toluene/xylene in good yields. This method offers a promising approach for repurposing waste tires as a renewable feedstock.