Polyurethane-Type Poly[3]rotaxanes Synthesized from Cyclodextrin-Based [3]Rotaxane Diol and Diisocyanates

Synthesis of polyurethane-type poly[3]rotaxanes is achieved by polyaddition between a cyclodextrin (CD)-based [3]rotaxane diol and various diisocyanate species, which provide a more defined structure compared to conventional polyrotaxane syntheses. In this study, hydroxyl groups on CDs of [3]rotaxane diol are initially acetylated, and deprotected after the polyaddition to introduce polyurethane backbone structure into polyrotaxane framework. Despite a relatively complicated chemical structure, [3]rotaxane diol monomer is successfully synthesized in a high yield (overall 67%) without any taxing purification process, which is beneficial for practical applications. The polymerization itself proceeds well under a standard polyaddition reaction condition to afford corresponding polyurethanes around 80% yield with M_n > 30 kDa. The poly[3]rotaxanes show different aggregation behavior or optical properties, whether or not acetyl groups are present, and are analyzed by XRD, SEM, and fluorescence measurements.