Heat‐induced Supramolecular Crosslinking of Dumbbell‐shaped PEG with β‐CD Dimer Based on Reversible Loose‐fit Rotaxanation

Abstract

Supramolecular crosslinking was studied in reversible loose‐fit rotaxanation between a size‐mismatched ring and a dumbbell‐shaped chain attached to bulky terminals through slipping of the crosslinked rings onto the chain using a combination of β‐cyclodextrin (β‐CD) and poly(ethylene glycol) (PEG) in water. The mixing led to a drastic increase in viscosity only at an elevated temperature, while a PEG chain without any terminals or with bulkier terminals produced no change in the mixed solution under the same conditions. The dynamic viscoelastic properties of the mixed solution of the proper dumbbell‐shaped PEG chain and β‐CD dimer in water were also investigated to indicate network formation through heat‐induced supramolecular crosslinking. magnified image

Modulation of reversible self-assembling of dumbbell-shaped poly(ethylene glycol)s and β-cyclodextrins: precipitation and heat-induced supramolecular crosslinking

“…The ditopic crosslinker 4 was prepared by attachment of monoaminated permethylated b-CD to each end of PEG (average l¼7) bis(carboxymethyl) ether through a condensation reaction. 17 The tetratopic crosslinker 5 was prepared by repeated 1,3-dipolar cycloaddition reactions 23,24 of monoazidated permethylated b-CD 8 20 and quadruply-azidated pentaerythritol ethoxylate 10 (average a+b+c+d¼15) at the respective ends of PEG (average m¼9) bis(prop-2-ynyl) ether 7 (Scheme 3).…”

“…If we consider the hydrophobic inherence in 1a, whose solution is turbid in water at any temperature, the solubilization would be accounted for by assuming inclusion complexation with 3 at least at the end of 1a. 17 It would be difficult to judge whether the methylated b-CD was trapped onto 1a or not from only the appearance due to high water solubility of 3. 18 Similar results were obtained from mixing of 1b with 2 or 3 qualitatively, in terms of precipitation or solubilization ( Table 1).…”

“…In addition, cyclic molecules would stay on chains cooperatively when they were crosslinked by a spacer, leading to a supramolecular network through the pseudopolyrotaxane formation (Scheme 1c). [13][14][15][16][17] Here we report the roles of barriers at the ends of a chain, and crosslinking of cyclic molecules in self-assembly of size-mismatched components, PEG and b-CD. [17][18][19] We investigated systematically the pseudopolyrotaxane formation of a series of dumbbell-shaped PEG chains 1a-e with native b-CD 2 and its permethylated derivative 3 20 (Scheme 1b and Figure 1).…”

Loose‐Fit Polypseudorotaxanes Fabricated by γ‐CDs Threaded Onto a Single PNIPAAm‐PEG‐PNIPAAm Chain in Aqueous Solution

“…Furthermore, because CDs are nontoxic and biodegradable, they are widely used as additives for foods, cosmetics, and personal care items, and their pharmaceutical applications have been also explored. However, only a few investigations were devoted to the preparation of loose‐fit PRs formed from a mismatched polymeric chain fitting into the cavity of γ ‐CDs 24–26. As those γ ‐CDs are randomly entrapped on the polymeric chains showing no channel‐type crystal structure, they can not only easily slip and rotate along the included polymeric chain but also allow small molecules or other polymers, such poly(ethylene glycol) (PEG) and poly( ϵ ‐caprolactone) (PCL) to be contained into their cavity.…”

Cyclodextrin-based rotaxanes

“…One should point out that CD polyrotaxanes are large family which may be divided into species containing long polymer chains (such as PEG, PEO, PANI, PNIPA etc.) [36][37][38][39][40][41], and species without a long polymer chain, mainly oligorotaxanes [42][43][44][45][46][47]. The CD polyrotaxanes are a separate class of compounds and are not included here.…”