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Polymers produced by ring-opening metathesis polymerization (ROMP) of strained cyclic olefin monomers, such as norbornene and cyclobutene, are challenging to depolymerize back to their constituent monomers due to their favorable polymerization thermodynamics. Current strategies for creating depolymerizable ROMP polymers focus on designing low-strain monomers with small enthalpic driving forces, which facilitate depolymerization by reducing the monomer polymerizability. Because polymerization thermodynamics is governed by both enthalpic and entropic contributions, we reason that depolymerizable polymers could be achieved from highly strained cyclic olefin monomers if the entropic penalty of polymerization is sufficiently large. Here, we present a depolymerizable polymer system based on a series of strained bicyclo[3.2.1] monomers, which combine a substantial enthalpic driving force (−6 to −11 kcal/mol) with a significant entropic penalty of polymerization (−15 to −24 cal/mol/K). The large entropic penalty, arising from the rigid polymer backbone, lowers the ceiling temperature and imparts depolymerizability to the polymer system, leading to monomer recovery (74–99%) under standard ring-closing metathesis conditions. Moreover, the enthalpic driving force remains sufficient to enable efficient ring-opening metathesis polymerization and block copolymer synthesis. This entropy-driven strategy thus unlocks access to depolymerizable polymers from strained cyclic olefin monomers that are not traditionally considered building blocks for such materials, offering a new direction for the design of chemically recyclable polymers with an expanded monomer scope.
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Regulating cationic polymerization: From structural control to life cycle management
Cationic polymerization is a powerful strategy for the production of well-defined polymers and advanced materials. In particular, the emergence of living cationic polymerization has enabled pathways to complex polymer architectures inaccessible before. The use of light and electricity as external stimuli to regulate cationic polymerization represents another advance with increasing applications in surface fabrication and patterning, additive manufacturing, and other advanced material engineering. The past decade also witnessed vigorous progress in stereoselective cationic polymerizations, allowing for the dual control of both the tacticity and the molecular weight of vinyl polymers towards precision polymers. In addition, in addressing the plastics pollution crisis and achieving a circular materials economy, cationic polymerization offers unique advantages for generating chemically recyclable polymers, such as polyacetals, polysaccharides, polyvinyl ethers, and polyethers. In this review, we provide an overview of recent developments in regulating cationic polymerization, including emerging control systems, spatiotemporally controlled polymerization (light and electricity), stereoselective polymerization, and chemically recyclable/degradable polymers. Hopefully, these discussions will help to stimulate new ideas for the further development of cationic polymerization for researchers in the field of polymer science and beyond.
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- Award ID(s):
- 1944512
- PAR ID:
- 10497351
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Progress in Polymer Science
- Volume:
- 145
- Issue:
- C
- ISSN:
- 0079-6700
- Page Range / eLocation ID:
- 101736
- Subject(s) / Keyword(s):
- Living polymerization Organocatalysis Photocontrolled polymerization Electrocontrolled polymerization Stereoselective polymerization Sustainable materials
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1016/j.progpolymsci.2023.101736
