Dethreading during the preparation of polyrotaxanes

Abstract

Using a diol blocking group, bis@-terf-butylphenyl)bis[p-(2-(2-hydroxyethoxy)ethoxy)phenyl]methane (diol BG l), a diol with a sterically large core, copolysebacate 30-crown-I0 (30C10) rotaxanes 8, 9 and 10 were synthesized by incorporating different amounts of 1,IO-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 (mln value, the average number of cyclic molecules per repeating unit) increased with feed ratio of diol BG 1 vs. 1,lO-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.

A Strategy To Eliminate Dethreading during the Preparation of Poly(ester/crown ether rotaxane)s: Use of Difunctional Blocking Groups

“…Thus the only possible reason for the change of chemical shift of 30C10 before and after threading is the existence of a through-space interaction, which was well demonstrated in our previous work. 13,14 The 2D NOESY spectrum of polyrotaxane 17c (Figure 6) indeed shows a correlation similar to that observed in polyrotaxane 16. 13,14 The protons of threaded 30C10 (3.50 ppm signal) are correlated with the aromatic protons e′, f′, g′, h′, i′, and j′.…”

“…1 13 (14). Diacid BG 8 (4.70 g, 6.78 mmol) was dissolved in SOCl2 (50 mL), and the solution was refluxed for 3 h. Upon the removal of excess SOCl2, a yellow solid was obtained, which was recrystallized in hexane (150 mL) to give needle crystals (4.3 g, 88%), mp 138.6-140.0°C.…”

“…13,14 During the preparation of polyrotaxanes 17, as soon as 30C10 is threaded via the endo esterification of 5, it is confined between two BG units (structure 9) and no dethreading can occur to form unthreaded 8 and free crown ether (Scheme 2). Thus by using diacid chloride BG 14 and diol BG 15, a novel approach to eliminate dethreading during the polycondensation was introduced.…”

“…Experimentally, the degree of dethreading in the preparation of the polyrotaxanes of type 2 increased linearly as the proportion of diol BG in the total diol decreased. 14 It is expected that dethreading during the polyesterification period can be eliminated by using two bulky X Abstract published in Advance ACS Abstracts, August 1, 1997.…”

Catalytic Self-Threading: A New Route for the Synthesis of Polyrotaxanes

“…For all subsequent solution manipulations dethreading of the macrocycles becomes an issue. 13,53,54 To prevent this from happening, blocking ("stopper") groups have been incorporated either at both chain ends or as an integral part of the repeat unit along the polymer main chain classified as polyrotaxanes ( Figure 2). 55 An alternative to stoppering after pseudopolyrotaxane formation 31,56 is the use of prestoppered rotaxane monomers which are then polymerized [57][58][59][60][61][62] or the copolymerization of selfassembled pseudorotaxane monomers with mono-or difunctional stopper groups.…”