Dethreading during the preparation of polyrotaxanes

Abstract

Using a diol blocking group, bis(p-tert-butylphenyl)bis[p-(2-(2-hydroxyethoxy)ethoxy)phenyl]methane (diol BG 1), a diol with a sterically large core, copolysebacate 30-crown-10 (30C10) rotaxanes 8, 9 and 10 were synthesized by incorporating different amounts of 1,10-decanediol. These copolymeric rotaxanes were characterized by different techniques, including proton NMR spectra, hydrolytic recovery of 30C10 and 2D NOESY. It was found that threaded 30C10 displayed a range of chemical shifts corresponding to the various sequence structures in which it was constrained. In addition, it was proved that the threading efficiency (m/n value, the average number of cyclic molecules per repeating unit) increased with feed ratio of diol BG 1 vs. 1,10-decanediol. A linear relationship of threading or dethreading degree vs. the percentage of diol BG in the total diol feed was revealed; more BG, less dethreading. The results demonstrate that dethreading occurs during the polycondensation in the absence of BGs.