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

Area of Science:

• Polymer Physics
• Soft Matter Science
• Materials Science

Background:

• Ring polymers present unique topological challenges for studying polymer dynamics.
• Linear chain contaminants in ring polymer samples complicate experimental observations.
• Understanding the intrinsic dynamics of pure ring polymers is crucial for fundamental polymer physics.

Purpose of the Study:

• To investigate the stress relaxation dynamics of topologically pure, high molecular weight ring polymers.
• To elucidate the role of ring-ring interactions and packing structure in polymer dynamics.
• To overcome experimental challenges in preparing pure ring polymer samples.

Main Methods:

• Synthesis of topologically pure cyclic poly(phthalaldehyde) (cPPA) without linear contaminants.
• Linear viscoelastic measurements of concentrated cPPA solutions.
• Molecular dynamics (MD) simulations of high molecular weight ring polymers.

Main Results:

• Observed slow, non-power-law stress relaxation in concentrated pure ring polymers.
• MD simulations confirmed non-power-law dynamics and revealed significant ring-ring interpenetrations.
• Ring-ring interpenetrations were linked to inter-ring caging and slowed dynamics.

Conclusions:

• Concentrated pure ring polymers exhibit unique slow stress relaxation behavior.
• Ring-ring interpenetrations significantly influence polymer dynamics, contrary to single-ring conformations.
• This study provides new insights into the physics of ring polymers, particularly at high molecular weights.