Prolonged Glass Transition due to Topological Constraints in Polyrotaxanes

Topological constraints in polyrotaxanes significantly affected their glass transition dynamics. The effects of the constraints were systematically studied using a series of different coverage glass-forming polyrotaxanes consisting of a common polymer and threaded ring molecule of varying ratios. Although their ratios were similar and hence exhibited similar T-g values by differential thermal analysis, mechanical relaxation was considerably prolonged with increasing coverage. The relaxation became a two-step process: a faster step at a common temperature near the T-g and another which was prolonged by the coverage increase. Relaxation dynamics analysis revealed that segment motions, which are cooperative translations of different components, freeze at considerably higher temperatures than the T-g with increasing coverage. This suggests that although the rings are released from conventional interactions at the T-g, their cooperative translational motions are significantly constrained by the threading polymers with increasing coverage.