Synthesis and characterization of a polyester/crown ether rotaxane derived from a difunctional blocking group

A diol with a sterically large core, namely bis(p-tert-butylphenyl)bis[p-(2-(2-hydroxyethoxy)-ethoxy)phenyl]methane (diol BG 7), was synthesized by a multiple step method and successfully used for the preparation of a sebacate-based polyester 30-crown-10 (30C10) rotaxane with blocking groups or stoppers along the backbone. It was found that the resulting polyrotaxane had a threading efficiency (m/n value, the average number of cyclic molecules threaded per repeat unit) 5 times as high as that without BG under the same conditions, which proved that the BG can effectively prevent threaded 30C10 from slipping off the polymeric backbone during the preparation of the polyrotaxane. Additionally, new evidence for the formation of the polyrotaxane was demonstrated, including a chemical shift of threaded 30C10 protons different from that of the unthreaded species, a through-space interaction between 30C10 and the backbone proved by 2D NOESY measurements, and hydrolytic recovery of 30C10.