Complex dynamics of hydrogen bonded self-assembling polymers

Supramolecular polymers, which are non-covalently bonded and formed by self association of di or trifunctional monomers exhibit, by virtue of quadruple hydrogen bonds, many of the properties of normal high molecular weight polymers, e.g. a dynamic rubber plateau. We focus on the molecular and cooperative dynamics of self-assembled linear polymers and networks, studied by broadband dielectric relaxation spectroscopy (DRS) in the frequency range from 10^-2 to 10⁶ Hz. The DRS analysis was backed up by dynamic mechanical and rheological experiments. In the high temperature region two loss processes (α and α*) show up, the relaxation times of which obey the Vogel-Fulcher-Tammann (VFT) law. The dielectric α process is related to the dynamic glass-rubber transition and is slightly faster than the corresponding mechanical α process. A slower (high-temperature) α* relaxation is identified as chemical, corresponding to the mean lifetime of the hydrogen bonded linkages in the supramolecular chains. Its relaxation time τ_α* was found to be 1 to 2 decades larger than the terminal flow relaxation time, indicating that the relaxation of an entire chain is dominated by the joint dynamics of many hydrogen bonds. The β relaxation, observed in both DRS and dynamic mechanical analysis (DMA) at temperatures below T_g, arises from the local junction dynamics of hydrogen bonded units in the glassy state. Details of the temperature dependence and the shape of the loss peaks of the α and α* relaxations will be discussed in terms of temporary physical networks and cooperativity