Effect of Topological Constraints on the Glass Transition Behaviors of Polyrotaxanes

We report here peculiar glass transition behaviors attributed to the topological interactions between two different components of a mechanically interlocked polymer. A new class of polymer glasses were recently materialized from polyrotaxanes, which are necklace-like supramolecules composed of a linear polymer and threaded cyclic molecules. Some of the glasses were ductile and extensible to more than four-folds in length because of the slipping of threading chains through the rings in the region where the stress is concentrated. The unique structural change forced by large deformation seems to relate to the molecular dynamics. In the glass transition regime, the relaxation mode is almost an Arrhenius dependence on temperature, suggesting negligible cooperativity of molecular motions. In addition, a new viscoelastic relaxation at slightly slower than the glass transition regime is generated, when the number of rings in a single threaded chain (so-called “coverage”) is increased. The slower relaxation is significantly prolonged by the increase in coverage. It suggests that the increased topological constraints between different components restrict the translational motions of the rings dragging the threading chain.