(639i) Rheology of Ring Polymers

The understanding of the rheology of circular or ring macromolecules remains limited to relatively small rings. Thus, for example, it is now recognized that rings of polystyrene of high enough purity from linear chain contamination may be limited to 240,000 g/mol [1]. Part of the reason for this is the difficulty in making large quantities of rings and fractionating them for macroscopic rheological measurements. Here we report on rings made by a novel reversible radical recombination polymerization (R³P) of poly(3,6-dioxa-1,8-octanedithiol) (polyDODT)[2,3], which produces ring polymers of high purity and high molecular weight. By making measurements of both the solution properties and the melt properties, we were able to determine the molecular weight response of the circular polyDODT to entanglement densities of near 300 per chain and we were able to make measurements into the nominal Rouse regime where the rings were unentangled. Our results are consistent with literature results that suggest that the viscosity follows the Rouse-like behavior to molecular weights well above the entanglement molecular weight of the linear analogs, similar to the results on polystyrene from Doi et al.[1,4,5] In addition, we find that at approximately 15 entanglements there is a change in response to a dependence of the viscosity from a M¹ dependence on molecular weight to a M⁶ dependence.

We have also made measurements of the plateau modulus of the rings as a function of concentration and find that it scales similarly to the behavior of linear chains, viz., G_N⁰ varies as concentration φ^2.3. On the other hand, the steady state recoverable compliance, while scaling over the entire molecular weight range as M², is nearly independent of concentration. For comparison in linear polymers J_s scales as M^-2.25.

[1] G.B. McKenna, D. Chen, S.C.H. Mangalara, D. Kong and S. Banik, “Some open questions in Polymer Physics,” Polymer Engineering and Science (2022). DOI: 10.1002/pen.25938.

[2] E.Q. Rosenthal-Kim, J.E. Puskas, Green polymer chemistry: Investigating the mechanism of radical ring-opening redox polymerization (R3P) of 3, 6-dioxa-1, 8-octanedithiol (DODT), Molecules, 20 (2015) 6504-6519.

[3] K. Molnar, H. Kim, D. Chen, C.A. Helfer, G. Kaszas, G.B. McKenna, J.A. Kornfield, C. Yuan, J.E. Puskas, PolyDODT: a macrocyclic elastomer with unusual properties, Polymer Chemistry, DOI (2022).

[4] Y. Doi, A. Matsumoto, T. Inoue, T. Iwamoto, A. Takano, Y. Matsushita, Y. Takahashi, H. Watanabe, Re-examination of terminal relaxation behavior of high-molecular-weight ring polystyrene melts, Rheologica Acta, 56 (2017) 567-581.

[5] Y.Doi, Re-examination of terminal relaxation behavior for high-molecular weight ring polystyrenes, RING POLYMERS Workshop, Crete, 2017.