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.
Highlights
Properties of polymers strongly depend on the architecture as well as on the molecular weight
The spherical shape of our bottlebrush polymer in the melt state was confirmed by small-angle neutron scattering (SANS), while for the dynamical investigations, a combination of dielectric spectroscopy (DS) and fast field cycling (FFC) nuclear magnetic resonance (NMR) was used
Small-angle neutron scattering experiments have been performed on a blend of isotopically labeled bottlebrush polymers, based on PDMS
Summary
Properties of polymers strongly depend on the architecture as well as on the molecular weight. The spherical shape of our bottlebrush polymer in the melt state was confirmed by small-angle neutron scattering (SANS), while for the dynamical investigations, a combination of dielectric spectroscopy (DS) and fast field cycling (FFC) nuclear magnetic resonance (NMR) was used. It consists of a B = 0.25 T electromagnet, offering a measurable Larmor frequency range of 10 kHz−10 MHz. Minimizing external influences, by increasing the distance between the electric control unit and the electromagnet by 1.5 m together with removing of magnetizable parts as far as possible, shifts the lower limit to 5 kHz. For the samples investigated here, a temperature range of T = −100 to +135 °C was used to create the master curves including the relaxation peak associated with the segmental relaxation. The samples were quenched in liquid nitrogen to minimize crystallization during the measurement
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