Sol-gel transition of hydrophobically modified polyrotaxane

The sol-gel transition and thermosensitivity of methylated polyrotaxane (Me-PR) aqueous solutions were investigated by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS). It is known that water-solubility of polyrotaxane (PR), consisting of polyethylene glycol) (PEG) and a-cyclodextrin (α-CD), is very low due to stacking of neighboring α-CD molecules on a PEG chain. Methylation of the hydroxyl groups on α-CD molecules resulted in a significant improvement of water-solubility, and Me-PR exhibited a thermoreversible sol-gel transition in water depending on the degree of methylation. For low degrees of methylation (≤ 30%), a Me-PR solution was transparent even up to 80°C. On the other hand, for high degrees of methylation (≥60%), it became opaque with increasing temperature and a gelation took place at high temperature. The temperature dependence of the sliding motion of α-CD molecules along the PEG chains and the mechanism of sol-gel transition are discussed on the basis of SANS and DLS results.