Host–guest chemistry of linked β-cyclodextrin trimers and adamantyl substituted poly(acrylate)s in aqueous solution

Abstract

¹H NMR spectroscopy, isothermal titration calorimetry and rheological studies show that the β-cyclodextrin (β-CD) groups of two linked β-cyclodextrin trimers, β-CD₃bz and β-CDen₃bz complex the adamantyl substituents and their tethers in 3.0 ± 0.1% substituted poly(acrylate)s to form intra- and inter-poly(acrylate) strand cross-links in aqueous solution. The structures of the linked-β-cyclodextrin trimers and the length of the tether between the adamantyl substituent and the poly(acrylate) backbone have substantial effects on the complexation constants, K, and the associated thermodynamic parameters. This is partially shown for the complexation by β-CD₃bz of the adamantyl substituents as tether length varies from –CONH– (3.45 × 10⁴) through –CONH(CH₂)_nNHCO– where n = 2 (2.09 × 10⁵), 6 (3.17 × 10⁵) or 12 (7.46 × 10⁴) in 0.13–0.37 wt% substituted poly(acrylate) solutions and the figures in brackets are the K in dm³ mol⁻¹ at 298.2 K. For the same sequence of substituted poly(acrylate)s the variation of viscosity is: 0.03, 3.78, 3.48, and 2.03 Pa s⁻¹ at 500 s⁻¹ shear rate at 298.2 K for 5.0 wt% substituted poly(acrylate) solutions in which the β-CD groups of β-CD₃bz and the adamantyl substituents are equimolar at 1.5 × 10⁻² mol dm⁻³. The eight data sets for the β-CD₃bz and β-CDen₃bz systems are discussed in terms of host–guest interactions between the host β-CD groups and the guest adamantyl substituents of the substituted poly(acrylate)s and are compared with those for the analogous β-CD systems.