Control of the dynamics in polymer materials is crucial for the mechanical properties as well as the control of higher-order structures. From the aspect of unique molecular motions, mechanically interlocked polymers, such as polyrotaxanes, have been expected to show unique mechanical properties. We report here that a new class of glassy polyrotaxanes named “polyrotaxane glass” show unique viscoelasticity and tensile behaviors attributed to their intramolecular potential motions. Appropriate chemical modifications to the cyclodextrins (CDs) that are the cyclic components threaded with end-capped polyethylene glycol (PEG) yielded thermo-plastic polyrotaxanes. The polyrotaxanes were thermal press-molded to obtain glassy films. The polyrotaxane glass exhibited almost constant Young’s modulus of about 1 GPa at room temperature, and the glass transition temperature (T<sub>g</sub>) is variable from 270 to 370 K depending on the substituents on CDs. The glass transition dynamics was almost Arrhenius-type, whereas the increase in apparent activation energy toward T<sub>g</sub> was generally observed in conventional polymers. The sub-relaxation strength and the dynamics were constant as long as the backbone polymer and the coverage were the same. Notably, the unique viscoelasticity was not observed without the backbone. It indicates that large motions of the backbone PEG remain in the glassy frameworks formed by their cyclic components to generate the significant sub-relaxation. Under uniaxial tensile, the polyrotaxane glass showed crazing that accompanies the formation of nanoscale voids and fibrils and were extensible to &gt;300% strain. In-situ X-ray scattering study under the tensile tests revealed that the microphase separation between CDs and naked PEG domains was induced by the deformation, as a result of the sliding of PEG through the cavity of CDs.

Peculiar viscoelasticity and tensile behavior of polyrotaxane glass

253rd National Meeting (2017)

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