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Rheological Isotope Effects for Molecular Insight in Covalent Adaptable Networks.

Christina M Hemmingsen1, Steven J Chapman1, Chuting Deng2

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This summary is machine-generated.

Rheological isotope effects (RIEs) reveal how dynamic covalent bond exchange influences polymer network properties. Deuterium substitution accelerates bond exchange and stress relaxation in covalent adaptable networks (CANs), offering new insights into viscoelasticity.

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Area of Science:

  • Polymer Science
  • Materials Chemistry
  • Physical Chemistry

Background:

  • Bridging the gap between small-molecule reactivity and bulk polymer properties is a key challenge.
  • Viscoelasticity in covalent adaptable networks (CANs) is linked to dynamic covalent bond exchange, but network effects complicate this relationship.
  • Direct molecular-level study of bond exchange in polymer networks is limited.

Purpose of the Study:

  • Introduce rheological isotope effects (RIEs) as a novel molecular tool to probe dynamic covalent exchange in bulk polymer networks.
  • Quantify the impact of deuterium substitution on stress relaxation dynamics in dithioalkylidene-based CANs.
  • Investigate the influence of network topology and defects on the relationship between bond exchange and viscoelasticity.

Main Methods:

  • Utilized swelling of dithioalkylidene-based CANs in H2O vs. D2O to perturb thiol/thiolate equilibrium.
  • Measured stress relaxation rates in bulk polymer networks using rheology.
  • Employed Monte Carlo simulations to model network formation and analyze topological defects.

Main Results:

  • RIEs were observed in poly(ethylene glycol)-based CANs, with stress relaxation rates varying from 0.31 to 0.64.
  • Deuterium substitution accelerated bond exchange and stress relaxation, confirming the sensitivity of the system to isotopic effects.
  • Monte Carlo simulations suggested that topological defects, such as bridging chains, reduce the impact of bond exchange on stress relaxation.

Conclusions:

  • RIEs provide a powerful new method for studying dynamic covalent exchange mechanisms in bulk polymer networks.
  • The study elucidates how network defects influence viscoelastic properties by modulating the dependence on bond exchange.
  • RIEs offer a pathway to deconvolute stress relaxation modes and understand defect impacts in complex CANs.