Polyrotaxanes: Past, present and future

Abstract

Abstract:The threading process in polysebacatecrown 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 dol, 4) the length of the am-diol and 5) the temperature of equilibration and reaction. It was concluded that the threading process is based on hydrogen bonding interactions of the do1 with the crown ether, predisposing the latter to threading as the ester bond is formed. The hdc of "stoppers" or "knots" at the chain ends is believed to albw 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 30crown-10 case, display crystalline phases for both the backbone and the cyclic components. All of the polyrotaxanes complex alkali metal ions.

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

“…Bis(p-tert-butylphenyl)bis[p-((5-carbethoxypentyl)-oxy)phenyl]methane (12). Bis(p-tert-butylphenyl)bis(p-hydroxyphenyl)methane (10) (5.00 g, 10.8 mmol) in DMF (50 mL) Figure 5.…”

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

“…1,[16][17][18][19]21,60 Key to our methodology is a chemically and thermally exceptionally robust macrocycle that has been in scientific hibernation since its first synthesis by Behrend et al in 1905. 78 The seminal work by Mock et al [79][80][81][82][83][84][85][86][87][88][89] in the 1980s brought this unusual molecule, to which the name of cucurbituril (now cucurbit [6]uril) was given in analogy to its shape being reminiscent of that of a gourd or pumpkin ( Figure 3), to the attention of the supramolecular chemistry community. [90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] Cucurbit [6]uril possesses a unique set of molecular recognition modes as a consequence of its rigid, nonadecacyclic shape, hydrophobic interior, and two hydrophilic oculi formed by a set of six equidistant carbonyl groups, each set aiming at a common focal point located approximately 10 Å away from the macrocycle's center of gravity.…”

“…89,93 The opening of each portal is close to 4 Å in diameter through which small molecules can enter the interior. 80,83,108 Modifications along the equatorial perimeter of cucurbit [6]uril have rendered it soluble in organic solvents. 109,110 Larger members of the cucurbituril family have been explored as new hosts for supramolecular assemblies.…”

“…109,110 Larger members of the cucurbituril family have been explored as new hosts for supramolecular assemblies. 105,[111][112][113][114] Cucurbit [6]uril itself binds strongly to a variety of main-group [115][116][117][118] and transition-metal 119,120 ions and to aliphatic 80,[83][84][85]121,122 and aromatic mono-and diammonium ions, 80,[83][84][85][123][124][125] primarily through ion-dipole interactions. Although the interior is hydrophobic toward the center of the cavitand, it gradually becomes more hydrophilic toward the carbonyl groups.…”

“…Although the interior is hydrophobic toward the center of the cavitand, it gradually becomes more hydrophilic toward the carbonyl groups. 107 The latter are part of the cyclic urea moieties which are responsible for the highly hygroscopic nature of cucurbit [6]uril. 97 The property that distinguishes cucurbit [6]uril from any of the typical macrocycles (cyclodextrins, crown ethers, cyclophanes) is its remarkable ability to catalyze 1,3-dipolar cycloadditions in a regioselective manner (Figure 4).…”