Dielectric Relaxation and Rheological Behavior of Supramolecular Polymeric Liquid Nan Lou, † Yangyang Wang, ‡ Xiaopeng Li, §,∥ Haixia Li, † Ping Wang, ⊥ Chrys Wesdemiotis, § Alexei P. Sokolov, ‡ and Huiming Xiong* ,† † Department of Polymer Science, Shanghai Jiao Tong University, Shanghai 200240, P. R. China ‡ Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States § Department of Chemistry and Polymer Science, University of Akron, Akron, Ohio 44325, United States ∥ Department of Chemistry and Biochemistry, Texas State University, San Marcos, Texas 78666, United States ⊥ Dow Chemicals Company Limited, Shanghai 201203, P. R. China * S Supporting Information ABSTRACT: A model self-complementary supramolecular polymer based on thymine and diamidopyridine triple hydrogen-bonding motifs has been synthesized, and its dielectric and rheological behavior has been investigated. The formation of supramolecular polymers has been unequivocally demonstrated by nuclear magnetic resonance, electrospray ionization mass spectrometry with traveling wave ion mobility separation, dielectric spectroscopy, and rheology. The dynamical behaviors of this associating polymer generally conform to those of type-A polymers, with a low-frequency chain relaxation and a high-frequency α relaxation visible in both rheological and dielectric measurements. The dielectric chain relaxation shows the ideal symmetric Debye-like shape, resembling the peculiar features of hydrogen-bonding monoalcohols. Detailed analysis shows that there exists a weak decoupling between the mechanical terminal relaxation and dielectric Debye-like relaxation. The origin of the Debye-like dielectric relaxation is further discussed in the light of monoalcohols. ■ INTRODUCTION Supramolecular polymers have continuously attracted consid- erable attention due to their fundamental and technological importance. In contrast to conventional polymers made of covalently bonded backbones, supramolecular polymers are formed by linking monomers with reversible and relatively weak noncovalent interactions such as hydrogen bonding, metal coordination, and π−π interaction. 1−13 The reversible nature of these noncovalent bonds brings about extra complexity, making the understanding of local and global dynamics a challenge. While a lot of effort has been devoted to constructing supramolecular polymers through diverse structural building blocks, much less attention has been paid to the dynamics of this important class of material. For example, the dielectric behavior of supramolecular polymers has rarely been reported. 14,15 On the theoretical side, numerous models have proposed to describe the dynamical behavior of supramolecular or “living” polymers 16−22 and associating polymers 23−31 in general. However, direct comparison between theory and experiment, especially for supramolecular polymer in un- entangled state, is still quite limited. 17,22,27 In this article, we report the dielectric and rheological behavior of a model self-complementary supramolecular polymer which is based on the triple hydrogen-bonding thymine and diamidopyridine motifs. 32 In contrast to the widely studied ureidopyrimidone-based (UPy) materials, 33 the strength of hydrogen-bonding interaction of T-DAP9 is in the medium range, bridging between that of UPy and hydrogen bonds of single valence. Besides, this supramolecular polymer appears completely amorphous in the molten state with a thermal glass transition temperature around 0 °C and thus may serve as a model system for the study of dynamics of this class of associating liquid. The formation of supramolecular polymer is confirmed by solution nuclear magnetic resonance, electro- spray ionization mass spectrometry with traveling wave ion mobility separation, dielectric spectroscopy, and rheology. The dielectric spectrum of the supramolecular polymer typically consists of a prominent Debye-like relaxation and a weak high- frequency relaxation, similar to what has been observed in hydrogen-bonding liquids such as monoalcohols, whose exact nature has remained a “puzzle” for one century. 34 The Debye- like process is found to be closely related to zero-shear viscosity, whereas the high-frequency process is identified as the structural relaxation. The general rheological and dielectric Received: January 13, 2013 Revised: February 20, 2013 Published: April 3, 2013 Article pubs.acs.org/Macromolecules © 2013 American Chemical Society 3160 dx.doi.org/10.1021/ma400088w | Macromolecules 2013, 46, 3160−3166