Polymer networks assembled by host-guest inclusion between adamantyl and β-cyclodextrin substituents on poly(acrylic acid) in aqueous solution

Polymer networks have been constructed through host-guest inclusion between β-cyclodextrin (p-CD) and 1-(2-aminoethyl)amidoadmantyl (ADen) substituents on poly (acrylic acid) (PAA). The structure of the networks and the host-guest interactions between the β-CD and ADen groups were studied by rheology and 2D H NOESY NMR spectroscopy. The maximum viscosity of the mixture of β-CD substituted PAA (β-CDPAA) and ADen substituted PAA (ADenPAA) occurred at a 1:1 β-CD:ADen substituent ratio which confirmed their binary inclusion. The viscosity of the mixture of the two polymers decreased upon addition of native β-CD due to its ability to compete favorably with the β-CD substituents of β-CDPAA in the inclusion of the ADen substituents of ADenPAA and the consequent disintegration of the polymer network. The rheological properties of the polymer networks were temperature sensitive. In the temperature range 10-35°C, the storage modulus and the loss modulus obeyed a time-temperature superposition. The horizontal and vertical temperature shift factors, a_T and b_T, obeyed a simple Arrhenius relationship for which the activation energies were found to be 70.3±0.4 and -2.2±0.1 kJ mol^-1, respectively. 2D ¹H NOESY NMR studies showed the ADen substituent to be included within the native β-CD and β-CD substituent cavities.