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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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Stereosequenced crystalline polyhydroxyalkanoates from diastereomeric monomer mixtures
Stereoselective polymerization of chiral or prochiral monomers is a powerful method to produce high-performance stereoregular crystalline polymeric materials. However, for monomers with two stereogenic centers, it is generally necessary to separate diastereomers before polymerization, resulting in substantial material loss and added energy cost associated with the separation and purification process. Here we report a diastereoselective polymerization methodology enabled by catalysts that directly polymerize mixtures of eight-membered diolide (8DL) monomers with varying starting ratios of chiral racemic ( rac ) and achiral meso diastereomers into stereosequenced crystalline polyhydroxyalkanoates with isotactic and syndiotactic stereodiblock or stereotapered block microstructures. These polymers show enhanced ductility and toughness relative to polymers of pure rac -8DL, subject to tuning by variation of the diastereomeric ratio and structure of the 8DL monomers.
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- Award ID(s):
- 1664915
- PAR ID:
- 10199903
- Date Published:
- Journal Name:
- Science
- Volume:
- 366
- Issue:
- 6466
- ISSN:
- 0036-8075
- Page Range / eLocation ID:
- 754 to 758
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1126/science.aax8466
