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 Tg 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 Tg 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 Tg with increasing coverage. This suggests that although the rings are released from conventional interactions at the Tg, their cooperative translational motions are significantly constrained by the threading polymers with increasing coverage.