depolymerizable-olefinic-polymers-based-on-fused-ring-cyclooctene

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. ...

University of Akron

A promising solution to address the challenges in plastics sustainability is to replace current polymers with chemically recyclable ones that can depolymerize into their constituent monomers to enable the circular use of materials. Despite some progress, few depolymerizable polymers exhibit the desirable thermal stability and strong mechanical properties of traditional polymers. Here we report a series of chemically recyclable polymers that show excellent thermal stability (decomposition temperature >370 °C) and tunable mechanical properties. The polymers are formed through ring-opening metathesis polymerization of cyclooctene with a trans-cyclobutane installed at the 5 and 6 positions. The additional ring converts the non-depolymerizable polycyclooctene into a depolymerizable polymer by reducing the ring strain energy in the monomer (from 8.2 kcal mol in unsubstituted cyclooctene to 4.9 kcal mol in the fused ring). The fused-ring monomer enables a broad scope of functionalities to be incorporated, providing access to chemically recyclable elastomers and plastics that show promise as next-generation sustainable materials.

Olefin metathesis-based chemically recyclable polymers enabled by fused-ring monomers.

While depolymerizable polymers have been intensely pursued as a potential solution to address the challenges in polymer sustainability, most depolymerization systems are characterized by a low driving force in polymerization, which poses difficulties for accessing diverse functionalities and architectures of polymers. Here, we address this challenge by using a cyclooctene-based depolymerization system, in which the cis-to-trans alkene isomerization significantly increases the ring strain energy to enable living ring-opening metathesis polymerization at monomer concentrations ≥0.025 M. An additional trans-cyclobutane fused at the 5,6-position of the cyclooctene reduces the ring strain energy of cyclooctene, enabling the corresponding polymers to depolymerize into the cis-cyclooctene monomers. The use of excess triphenylphosphine was found to be essential to suppress secondary metathesis and depolymerization. The high-driving-force living polymerization of the trans-cyclobutane fused trans-cyclooctene system holds promise for developing chemically recyclable polymers of a wide variety of polymer architectures.

Overcoming the Low Driving Force in Forming Depolymerizable Polymers through Monomer Isomerization.

Chemical recycling to monomer (CRM) is a promising route for transitioning to a circular polymer economy. To develop new CRM systems with useful properties, it is important to understand the effects of monomer structure on polymerization/depolymerization behavior. In earlier work, this group demonstrated chemically recyclable polymers prepared by ring-opening metathesis polymerization of trans-cyclobutane fused cyclooctenes (tCBCO). Here, it is investigated how different substituents on cyclobutane impact the thermodynamics and thermal properties of tCBCO polymers. Introducing additional substituents to a cis-diester functionalized tCBCO is found to favor the conversion of polymerization; increased polymerization conversion is also observed when the cis-diester is isomerized into its trans counterpart. The effects of these structural features on the thermal properties are also studied. These findings can provide important insights into designing next-generation CRM polymers.

Article	Year
Olefin metathesis-based chemically recyclable polymers enabled by fused-ring monomers. Nature chemistry\| PubMed ID: 34294914	2021
Overcoming the Low Driving Force in Forming Depolymerizable Polymers through Monomer Isomerization. Angewandte Chemie (International ed. in English)\| PubMed ID: 34499390	2021
Regulating the Thermodynamics and Thermal Properties of Depolymerizable Polycyclooctenes through Substituent Effects. Macromolecular rapid communications\| PubMed ID: 35686515	2022

Hanlin Chen

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