Crystal structure transition of polyrotaxanes attributable to competing rings and backbone induced by in situ modification of the backbone

In situ catalytic hydrogenation of polybutadiene-based polyrotaxane (BPR) that has 20% of its backbone covered with γ-cyclodextrin moieties induced a crystal structure transition attributed to competing crystal formations of the backbone and rings. Temperature- and time-controlled reactions of emulsified BPR with sodium dodecyl sulphate (SDS) yielded hydrogenated BPRs (H-PRs) with different degrees of hydrogenation; homogeneous reactions resulted in lower degrees of hydrogenation. The hydrogenation rate of BPR was higher than that of polybutadiene itself, indicating that the amphiphilic polyrotaxane with hydrophilic rings and a hydrophobic backbone is advantageous for the emulsion reaction. Crystallization of the H-PR backbones was detected by differential scanning calorimetry and the amount of heat generated increased with increasing degree of hydrogenation. Powder X-ray diffraction revealed that the crystal structures resemble orthorhombic polyethylene and the crystals of the ring components decreased with hydrogenation. This demonstrates that in situ hydrogenation of BPR endows the backbone with sufficient crystallinity to compete with the crystalline rings that generally govern the entire crystal structures of polyrotaxanes through efficient hydrogen-bonding networks that are independent of the backbones.