Effect of Topological Constraint and Confined Motions on the Viscoelasticity of Polyrotaxane Glass with Different Interactions between Rings

Abstract

A series of polyrotaxane glasses composed of poly(ethylene glycol) backbones and threaded α-cyclodextrins (α-CDs) with different substituents were found to exhibit unique viscoelasticities attributed to their interlocked structures, beyond a mere miscible blend of the different components. Differences in the interactions between CDs, which occupied 80 wt % or more of the materials, brought about wide variations in the glass transition temperature and also influenced the cooperativity of segmental motions of the polyrotaxanes near Tg. These polyrotaxane melts typically showed negligible cooperativity compared to conventional polymers, behaving as so-called “strong” glass formers. The cooperativity gradually emerged with increasing interaction strength between CDs, and elimination of the threading polymer resulted in “fragile” glass formers. These results suggest that the cooperative motion can be shielded by the topological constraint of the threading polymer, whereas the increasing dominance of convention...