Short-Time Dynamics of PDMS- g-PDMS Bottlebrush Polymer Melts Investigated by Quasi-Elastic Neutron Scattering

Karin J Bichler; Bruno Jakobi; Victoria García Sakai; Alice Klapproth; Richard A Mole; Gerald J Schneider

doi:10.1021/acs.macromol.0c01846

Short-Time Dynamics of PDMS- g-PDMS Bottlebrush Polymer Melts Investigated by Quasi-Elastic Neutron Scattering

Macromolecules. 2020 Nov 10;53(21):9553-9562. doi: 10.1021/acs.macromol.0c01846. Epub 2020 Oct 20.

Authors

Karin J Bichler¹, Bruno Jakobi², Victoria García Sakai³, Alice Klapproth⁴, Richard A Mole⁴, Gerald J Schneider^{1

2}

Affiliations

¹ Department of Physics &Astronomy, Louisiana State University, Baton Rouge 70803, Louisiana, United States.
² Department of Chemistry, Louisiana State University, Baton Rouge 70803, Louisiana, United States.
³ ISIS Facility, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot OX11 0QX, U.K.
⁴ Australian Nuclear Science and Technology Organisation, New Illawarra Road, Lucas Heights 2234, New South Wales, Australia.

Abstract

We have studied the short-time dynamical behavior of polydimethylsiloxane (PDMS) bottlebrush polymers, PDMS-g-PDMS. The samples have similar backbone lengths but different side-chain lengths, resulting in a shape transition. Quasi-elastic neutron scattering was used to observe the dynamical changes inherent to these structural changes. The combination of data from three spectrometers enabled to follow the dynamics over broad frequency and temperature ranges, which included segmental relaxations and more localized motions. The latter, identified as the methyl group rotation, is described by a threefold jump model and shows higher activation energies compared to linear PDMS. The segmental relaxation times, τ_s, decrease with increasing molecular weight of the side chains but increase with momentum transfer, Q, following a power law, which suggests a non-Gaussian behavior for bottlebrush polymers.