Paper Number
SM29 

Session
Polymers Solutions, Melts and Blends

Title
Unexpected slow relaxation dynamics of pure ring polymers

Presentation Date and Time
October 11, 2022 (Tuesday) 3:45

Track / Room
Track 2 / Sheraton 3

Authors (Click on name to view author profile)

1. Schroeder, Charles M. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)
2. Tu, Michael Q. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Charles M. Schroeder and Michael Q. Tu
Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Schroeder, Charles M.

Keywords
experimental methods; polymer melts; polymer solutions; recyclable polymers

Text of Abstract
Ring polymers are a unique class of macromolecules that lack free ends and show qualitatively different dynamics compared to linear polymers. Despite recent progress, we lack a complete understanding of the non-equilibrium flow behavior of ring polymers. In this talk, we discuss recent work from our group that has revealed unexpected surprises on ring polymer dynamics in highly concentrated polymer samples. In particular, we report new physics in the stress relaxation dynamics of pure, high molecular weight (MW) synthetic ring polymers using a combination of polymer synthesis, chemical characterization, bulk rheology, and analytical modeling. In recent years, experimental progress on understanding high MW synthetic ring polymers has been hindered due to the presence of linear contaminants. To overcome this challenge, we use cyclic poly(phthalaldehyde) (cPPA), a low-ceiling temperature polymer chemistry that rapidly depolymerizes from free ends, resulting in topologically pure kinetically-trapped metastable ring polymers. Linear viscoelastic (LVE) measurements of densely concentrated samples of high MW, pure synthetic rings show unexpected slow stress relaxation dynamics, despite the lack of linear contaminants. Experimental data show a plateau in the stress relaxation modulus G(t), which is qualitatively different than all previously reported data on ring polymer melts, which are predicted to show a power-law relaxation decay consistent with prevailing theories such as the fractal loopy globule model. Experimental results are complemented by molecular dynamics simulations of ring polymers of unprecedented molecular weights (with Thomas O’Connor), in addition to analytical arguments based on weak-caging theory for unconcatenated rings (with Kenneth Schweizer). Our results suggest that as ring polymers increase in MW or locally stiffen, inter-ring interpenetrations increase, which ultimately drive the new and unexpected relaxation behavior that is not captured in existing theoretical models for ring polymer melts.