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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, τs, 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.
Highlights
Bottlebrush polymers, i.e., linear side chains covalently bonded to a linear backbone, have received great interest in recent times
We have investigated the short-time dynamics of polydimethylsiloxane (PDMS)-based bottlebrush polymers, PDMS-g-PDMS, for the first time, by quasi-elastic neutron scattering (QENS)
By comparing the glass-transition temperature, determined by dielectric spectroscopy by Jakobi et al.[12] (Table 3), with the measurement temperature of Figure 3a,b, it reveals that these two temperatures are below Tg, the segmental dynamics are frozen
Summary
Bottlebrush polymers, i.e., linear side chains covalently bonded to a linear backbone, have received great interest in recent times These architectural modifications cause shape changes, such as from spherical into elongated objects, by varying the size ratio of backbone to side-chain length.[1−7] Inherent with the bottlebrush architecture are extraordinary properties, such as super softness or low viscosity. These properties are desirable in the development of new materials. The existence of the shape transition in these samples has been confirmed by smallangle neutron scattering (SANS) experiments.[12]
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