Complexation of Bisphenol A with Calix[6]arene‐Polymer Conjugates

Sodium calix[6]arenehexasulfonic acid (SCX 6 ) was introduced into polymer molecules by the cross‐linking of SCX 6 with epichlorohydrin (PolySCX 6 ) or by the covalent binding of carboxymethylated SCX 6 to an amino group‐carrying vinyl polymer (Poly(SCX 6 HMA‐ co ‐AAm)). The complexation of bisphenol A (BPA) with the SCX 6 group in the polymers was examined fluorimetrically using acridine red (AR) as a probe. From the inhibitory effect of BPA on the complexation of AR with the SCX 6 group in the polymers, the association constant ( K assoc ) of BPA with the SCX 6 group was evaluated and the value for BPA with the SCX 6 group in Poly(SCX 6 HMA‐ co ‐AAm) was much larger than that with the non‐conjugated SCX 6 , probably because of the support of hydrophobic interactions between the guest and the hydrocarbon moieties in the polymer (polymer main chain and hexamethylene groups introduced for the conjugation of SCX 6 ). The K assoc value for bisphenol B (BPB) with a non‐conjugated SCX 6 was larger than those for bisphenol A and bisphenol F, because of the higher hydrophobicity of BPB among the bisphenols examined. Thermodynamic parameters indicated that the inclusion of BPA into the cavity of sodium propyloxycalix[6]arenehexasulfonic acid (SPCX 6 ) was enthalpy driven, and the entropy change was largely negative (−92 J · mol −1  · K −1 ). This is probably because of a tight fit of guest molecules in the SPCX 6 cavity, resulting in the loss of freedom of both the SPCX 6 and the guest molecules. The entropy change for the complexation of BPA with the SCX 6 group in the polymer was less negative, probably because of a partial release of water molecules around the SCX 6 group upon the complexation. The effect of the structure of guest and host molecules on the complexation was also examined.Chemical structure of various calix[6]arenes: R = H, sodium calix[6]arenehexasulfonic acid; R = C 3 H 7 , sodium propyloxycalix[6]arenehexasulfonic acid; R = C 4 H 9 , sodium butyloxycalix[6]arenehexasulfonic acid; R = C 6 H 13 , sodium hexyloxycalix[6]arenehexasulfonic acid.