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John Torkelson

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Reprocessable polymer networks

Recycling of cross-linked polymeric materials, especially rubber tires, is a long-standing worldwide problem. Usually conventional cross-linked materials are composed of fixed covalent bonds, which limit the recyclability. We developed a novel synthetic approach using nitroxide-mediated polymerization to prepare cross-linked materials where nitroxide species serve as thermally reversible cross-links. Resulting materials can exhibit controlled network topologies and be recycled multiple times at 130 degree C - 140 degree C with minor property losses. Using styrene and polybutadiene, which are components of tire, the synthesized rubbers show nearly perfect property retention after recycling. The methodology of using controlled radical polymerization to produce reprocessable cross-linked materials has the potential to solve the tire recycling problem and stimulate the development of polymer networks with controlled topology.

K. Jin, L. Li, J.M. Torkelson, "Recyclable Cross-Linked Polymer Networks via One-Step Controlled Radical Polymerization," Advanced Materials, 28, 6746-6750 (2016). [Link]