Dynamical Comparison of Different Polymer Architectures-Bottlebrush vs Linear Polymer.

Abstract

Different polymer architectures behave differently regarding their dynamics. We have used a combination of dielectric spectroscopy, and fast field cycling nuclear magnetic resonance (NMR) to compare the dynamical behavior of two different polymer architectures, with similar overall molecular weight. The systems of interest are a bottlebrush polymer and a linear one, both based on poly(dimethylsiloxane) (PDMS). To verify the structure of the PDMS-g-PDMS bottlebrush in the melt, small-angle neutron scattering was used, yielding a spherical shape. Information about the segmental dynamics was revealed by dielectric spectroscopy and extended to higher temperatures by fast field cycling NMR. One advantage of fast field cycling NMR is the detection of large-scale chain dynamics, which dielectric spectroscopy cannot probe for PDMS. While segmental relaxation seems to be independent of the architecture, the large-scale chain dynamics show substantial differences, as represented by the mean square displacement. Here, two regions are detected for each polymer. The linear polymer shows the Rouse regime, followed by reptation. In contrast, the bottlebrush polymer performs Rouse dynamics and diffusion in the available time window, and entanglement effects are completely missing.