Polymer Dynamics in Nanostructured Environments: Structure-Property Relations Unraveled by Dielectric Spectroscopy

Many polymers exhibit complex levels of molecular and supramolecular organization, particularly if their chemical structure shows an increased complexity itself. This internal nanoscale-structuring is often accompanied by altered dynamics which in turn affects the macroscopic performance. Using this to design highly desired properties, e.g., mechanical stability, transport functions or self-healing, requires a detailed understanding of the interrelation between chemical structure and the corresponding change in dynamics. A versatile tool to explore polymer dynamics is dielectric spectroscopy, as demonstrated in two examples. The first case is a semi-crystalline star-polymer with a polyhedral oligomeric silesquioxane core; due to the unusual architecture of this molecule, the partial crystallization constrains the chain conformations in the amorphous regions and results in an accelerated segmental relaxation-in stark contrast to the commonly observed slower dynamics in semi-crystalline polymers. A detailed analysis of the extracted relaxation time distribution (RTD) reveals three separate amorphous regions with different dynamics. In a second example, the impact of meso-phase separation in associating telechelic polymers is studied. The hydrogen-bonding end groups in these polydimethylsiloxane-based materials phase separate, which is accompanied by a tremendously broadened RTD indicating severe constraints on the segmental dynamics. Again, altered chain conformations are proposed which offer a qualitative explanation for the tremendously enhanced rubbery plateau found in complimentary shear modulus measurements. In both examples, beyond the severe impact of nanostructured environments on the dynamics, dielectric spectroscopy also reveals subtle structural details leading to an improved macroscopic mechanical performance.