Segmental Dynamics in Stiff-g-Flexible Bottlebrush Polymers

Linear side chains densely grafted onto a linear backbone, known as bottlebrushes, have attracted the focus of researchers due to their different behaviors compared to linear polymers. Not only the morphology differs significantly, also the dynamics changes. In our previous QENS experiment on PDMS-g-PDMS bottlebrushes, we found, that the segmental dynamics of the side chains slows down while increasing their lengths. Recent simulation work presents the same result for flexible-g-flexible systems, like PDMS-g-PDMS. However, changing the stiffness of the backbone reverses the behavior of the segmental relaxation times, i.e., an acceleration occurs while increasing the side chain length, as suggested by the simulation work.
Intrigued by this result, we propose to study the side chain length dependent segmental relaxation of a stiff-g-flexible system in the melt state. For that purpose, we synthesized bottlebrush polymers with the stiff polynorbornene (PNB) backbone and flexible polypropylene oxide (PPO) side chains, PNB-g-PPO. This combination enables the grafting-through method ensuring a grafting density of 100%.
Using different side chain lengths, at the same backbone length, allows to track the reversed dynamical behavior of the segmental relaxation by comparing the relaxation times in the available Q-range. Furthermore, the spatial resolution obtained via the Q-dependence allows to judge the heterogeneity of the sample and the influence arising from the stiff backbone.