Unusual Viscoelasticity in Polyrotaxane Glasses

This work characterizes the viscoelastic properties of glasses made from polyrotaxanes, a class of mechanically interlocked polymers possessing a bead-on-a-string structure. The rheology of polyrotaxane-based glasses in the devitrified state reveals an absence of elastic plateau over a large range of frequencies.The motivation for this investigation stems from a need to understand the processability of polyrotaxanes. These ”molecular necklaces”, without any modification, are crystalline due to the presence of strong hydrogen bonding between the cyclodextrin-based molecular beads. Similar to cellulose, which also exhibits strong hydrogen bonding, these materials do not flow when heated. Chemicalmodification of the cyclodextrins leads to the breakdown of hydrogen bonding which, in turn, reduces crystallinity
and renders the polyrotaxanes amorphous and glassy. XRD and DSC data confirm the amorphous nature of these polymers and reveal their glass transition temperatures. Understanding the rheology of these polyrotaxane glasses will help characterize their mechanical behavior over different temperatures and time scales while identifying optimal processing conditions for applications in advanced materials.