Unexpected Slow Relaxation Dynamics in Pure Ring Polymers Arise from Intermolecular Interactions

Michael Q. Tu, Oleg Davydovich, Baicheng Mei, Piyush K. Singh, Gary S. Grest, Kenneth S. Schweizer, Thomas C. O'Connor, Charles M. Schroeder

Research output: Contribution to journalArticlepeer-review

Abstract

Ring polymers have fascinated scientists for decades, but experimental progress has been challenging due to the presence of linear chain contaminants that fundamentally alter dynamics. In this work, we report the unexpected slow stress relaxation behavior of concentrated ring polymers that arises due to ring-ring interactions and ring packing structure. Topologically pure, high molecular weight ring polymers are prepared without linear chain contaminants using cyclic poly(phthalaldehyde) (cPPA), a metastable polymer chemistry that rapidly depolymerizes from free ends at ambient temperatures. Linear viscoelastic measurements of highly concentrated cPPA show slow, non-power-law stress relaxation dynamics despite the lack of linear chain contaminants. Experiments are complemented by molecular dynamics (MD) simulations of unprecedentedly high molecular weight rings, which clearly show non-power-law stress relaxation in good agreement with experiments. MD simulations reveal substantial ring-ring interpenetrations upon increasing ring molecular weight or local backbone stiffness, despite the global collapsed nature of single ring conformation. A recently proposed microscopic theory for unconcatenated rings provides a qualitative physical mechanism associated with the emergence of strong inter-ring caging which slows down center-of-mass diffusion and long wavelength intramolecular relaxation modes originating from ring-ring interpenetrations, governed by the onset variable N/ND, where the crossover degree of polymerization NDis qualitatively predicted by theory. Our work overcomes challenges in achieving ring polymer purity and by characterizing dynamics for high molecular weight ring polymers. Overall, these results provide a new understanding of ring polymer physics.

Original languageEnglish (US)
Pages (from-to)307-317
Number of pages11
JournalACS Polymers Au
Volume3
Issue number4
DOIs
StatePublished - Aug 9 2023
Externally publishedYes

Keywords

  • glassy dynamics
  • intermolecular correlations
  • polymer physics
  • ring polymers
  • stress relaxation

ASJC Scopus subject areas

  • Chemical Engineering (miscellaneous)
  • Chemistry (miscellaneous)
  • Materials Chemistry
  • Polymers and Plastics
  • Physical and Theoretical Chemistry
  • Organic Chemistry

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