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.