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Low‐strain cyclic olefin monomers, including five‐membered, six‐membered, eight‐membered, and macrocyclic rings, have been recently exploited for the synthesis of depolymerizable polyolefins via ring‐opening metathesis polymerization (ROMP). Such polyolefins can undergo ring‐closing metathesis depolymerization (RCMD) to regenerate their original monomers. Nevertheless, the depolymerization behavior of polyolefins prepared by ROMP of seven‐membered cyclic olefins, an important class of low‐strain rings, still remains unexplored. In this study, we demonstrate the chemical recycling of polyheptenamers to cycloheptene under standard RCMD conditions. Highly efficient depolymerization of polyheptenamer was enabled by Grubbs' second‐generation catalyst in toluene. It was observed that the monomer yields increased when the depolymerization temperature increased and the starting polymer concentration was reduced. A near‐quantitative monomer regeneration (>96%) was achieved within 1 h under dilute conditions (20 mM of olefins) at 60°C. Moreover, polyheptenamer exhibited a decomposition temperature above 430°C, highlighting its potential as a new class of thermally stable and chemically recyclable polymer materials.
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Functional Group Transformation Approach to Chemically Recyclable Polymers from Ultra-Low to Moderate Strain Monomers
Ring-opening metathesis polymerization (ROMP) has been widely used for the synthesis of functional polymers. However, most ROMP-derived polymers are nondepolymerizable, limiting their sustainability and eco-friendiness. While recent advances in designing low-strain cyclic olefin monomers have enabled the ROMP synthesis of depolymerizable polyolefins, the scope of these monomers remains limited due to the narrow range of ring strain energies (RSEs = 4.7–5.4 kcal/mol) required to allow both polymerization and depolymerization in a closed-loop recycling process. Herein, we present a new class of chemically recyclable polyolefins based on cycloheptene derivatives with RSEs ranging from 3.8 to 7.2 kcal/mol. The wide range of RSEs enabled the establishment of a structure–polymerizability–depolymerizability relationship, shedding light on the role of RSE in both polymerization and depolymerization. A functional group transformation (FGT) strategy, harnessing reversible ketone-to-acetal chemistry, was developed to overcome the low polymerizability of low-strain monomers and the moderate depolymerizability of polymers made from moderate-strain monomers. This FGT approach not only enhanced the chemical recycling of moderately depolymerizable polyolefins but also provided access to highly depolymerizable polyolefins that are challenging to synthesize through direct ROMP of ultralow strain monomers. Moreover, the thermal properties of the chemically recyclable polyolefins developed in this study are highly tunable, with a broad range of glass transition temperatures (−7 to 104 °C), highlighting their potential for various applications.
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- Award ID(s):
- 2316842
- PAR ID:
- 10582318
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Macromolecules
- ISSN:
- 0024-9297
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1021/acs.macromol.4c03248
