Rheology, Sticky Chain, and Sticker Dynamics of Supramolecular Elastomers Based on Cluster-Forming Telechelic Linear and Star Polymers

Abstract

We elucidate the properties of unentangled telechelic poly(isobutylene) (PIB) chains in bulk forming dynamic micellar networks mediated by endgroups capable of hydrogen-bonding and π–π interactions. The effects of the molecular architecture and type of endgroup on the properties of networks are studied by a combination of small-angle X-ray scattering (SAXS), rheology, low-resolution NMR, and dielectric spectroscopy (DS). It is found that star-shaped molecules form more time-stable networks with larger and somewhat more distantly arranged aggregates compared to their linear counterparts. Using stickers providing less hydrogen bonds speeds up terminal flow significantly, yet surprisingly, the nanoscale morphology, apparent activation energies, and the timescale of endgroup fluctuations probed by DS are very similar across the two sample series. The correlation of results from the three dynamic methods (rheology, NMR, and DS) thus fortifies previous findings for linear chains: (i) even for star molecules, terminal stress relaxation is governed by single-chain relaxation rather than the reorganization of whole micelles, and (ii) the cluster-related relaxation time accessed by DS has no trivial relation to the actual sticky bond lifetime, the determination of which is concluded to be an open problem.