Backbone Polarity Tunes Sticker Clustering in Hydrogen-Bonded Supramolecular Polymer Networks

• Published in: Macromolecules 2022-07, Vol.55 (13), p.5514-5526
• Main Authors: Ahmadi, Mostafa, Jangizehi, Amir, Seiffert, Sebastian
• Format: Article
• Language: English
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.2c00645

Many of the fascinating properties of natural materials emerge upon phase separation and clustering. However, biomimetic polymeric materials often demonstrate limited performances due to ignoring that hierarchy. Thus, there is a need to change the design paradigm from the simple integration of transient bonds to the engineering of structural hierarchy. To account for that, we develop an entangled hydrogen-bonded supramolecular polymer network, based on strong fourfold hydrogen-bonding ureidopyrimidinone (UPy) groups and poly­(n-butyl acrylate) chains, where the local polarity is systematically varied by incorporating free hydroxyl (OH) groups. The integration of UPy groups significantly changes the relaxation spectrum, from a standard Maxwellian terminal flow to a high-frequency plateau spanning over three decades and the emergence of an additional low-frequency plateau. The absence of first-order thermal transitions in DSC curves and the emergence of diffraction peaks at nanometer lengths in SAXS profiles imply the presence of unordered aggregates. The introduction of free OH groups, however, gradually removes the plateau at low frequencies and increases the high-frequency one. A basic tube-based model including the sticky Rouse and the contour length fluctuations that are hindered by a mean-field penalty is developed to explain relaxation steps of entangled chains in the presence of binary associations and their clustering. The obtained fit parameters provide a precious quantitative correlation between the structural characteristics and key material functions. Specifically, despite the UPy content increases the penalty of chain dynamics, the fraction of OH groups does not, due to the countereffects of promoting binary associations and reducing clustering.