A strategy to eliminate dethreading during the preparation of poly(ester/crown ether rotaxane)s: Use of difunctional blocking groups

A novel strategy to completely eliminate dethreading of captured cyclics during the preparation of polyrotaxanes has been developed. A new difunctional blocking group (BG), namely bis(p-tert-butylphenyl)bis[p-((5-(chlorocarbonyl)pentyl)oxy)phenyl]methane (diacid chloride BG 14), was prepared in an overall yield of 6% by a three-step method. BG 14 polymerized with bis[p-((2-hydroxyethoxy)ethoxy)phenyl]bis(p-tert-butylphenyl)methane (diol BG 15) using 30-crown-10 (30C10) as solvent to afford poly(ester rotaxane)s 17 with unique architectures having two BGs per repeat unit. The formation of the polyrotaxanes was proved by a chemical shift of threaded 30C10 different from that of unthreaded species, hydrolytic recovery of 30C10, and a 2D NOESY study and supported by the GPC analysis. It was found that the resulting polyrotaxanes 17 had threading efficiencies (m/n values, average number of cyclic molecules per repeat unit) 2 times as high as those of poly(ester rotaxane)s 16 made under the same conditions from diol BG 15 and sebacoyl chloride. By optimizing the conditions, the threading efficiency was increased to 0.172 in polyrotaxane 17c, almost 14 times as high as that (0.012) of the polyrotaxane of type 1 made from decanediol and sebacoyl chloride.