Polyrotaxanes: Past, present and future

The threading process in polysebacate-crown ether rotaxanes prepared by the acid chloride method was examined by systematic study of the effects of 1) the size of the macrocycle, 2) the equilibration time between the diol and the macrocycle before addition of sebacoyl chloride, 3) the molar ratio of crown ether to diol, 4) the length of the alpha,omega-diol and 5) the temperature of equilibration and reaction. it was concluded that the threading process is based on hydrogen bonding interactions of the diol with the crown ether, predisposing the latter to threading as the ester bond is formed. The lack of ''stoppers'' or ''knots'' at the chain ends is believed to allow loss of macrocycles in the initial precipitation, after which loss of macrocycles is very slow due to chain folding. All of these polyester rotaxanes, except the 30-crown-10 case, display crystalline phases for both the backbone and the cyclic components. All of the polyrotaxanes complex alkali metal ions.