Stretch-Induced Intramolecular Phase Separation in Polyrotaxane Glasses for the Mechanical Toughness

We present here a unique mechanism for ductile behavior observed in a new series of polymer glasses made only of polyrotaxanes, which are necklace-like mechanically interlocked polymers consisting of cyclic molecules and threading linear polymers. The polymer glasses exhibit a Young’s modulus of ca. 1 GPa and are ductile with crazing, necking and a total elongation of >300%. Synchrotron X-ray scattering measurements under uniaxial tensile test showed that an amorphous hallo corresponding to the correlation distance between the cyclic components was shifted to a lower q value parallel to the tensile direction, and then began to shift in the opposite direction as the transmittance was suddenly increased. It indicates that the cyclic components located at the necking part were approaching against the tensile direction. In addition, the threading polymers sparsely covered with the rings were orientated to the tensile direction and crystallized slowly. It is attributed to the continuously exposed polymers threading, because an aging with such crystallization was interfered by the distributed threaded rings. These results indicate that an intramolecular phase separation between the aggregated rings and the exposed polymers were induced at the stress concentrated to be toughened.