Polymers with cleavable groups in their backbones may be chemically recycled, may undergo biodegradation (e.g., in applications where loss of plastics into the environment cannot be avoided), and play a key role in the establishment of a circular plastics economy. Vinyl polymers are one of the most-used types of plastic but, due to their carbon–carbon backbones, are not degradable. The degradation of thermosets prepared through free radical polymerization remains a challenge since these have proven undegradable even if degradable crosslinkers are used. We demonstrate that radical copolymerization of vinyl monomers (methacrylates, acrylates, acrylamides, styrene, acrylonitrile, vinyl ethers) with thionolactones leads to well-defined copolymers containing a tuneable amount of backbone thioesters. The mechanism, termed thiocarbonyl addition–ring-opening (TARO) is compatible with RAFT and ATRP and also leads to degradable polymers through free radical polymerization. Unlike esters groups installed into copolymers through traditional radical ring-opening polymerization methods, the thioesters produced through TARO can be selectively cleaved through aminolysis, thiolysis, and oxidation without harming side group esters. Gels prepared through free radical copolymerization of the thionolactone dibenzo[c,e]oxepane-5-thione (DOT), acrylates, and a difunctional crosslinker had similar thermal properties as gels prepared without DOT but could be degraded into fully soluble fragments under mild conditions. This strategy thus offers a route for the recycling of thermoset plastics in a circular economy.

Incorporating labile thioester functionality into vinyl copolymers: Toward recycling of linear and crosslinked polymers

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ACS Fall 2022

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