Synthesis of polymeric crown ethers and thermoregulated ion complexation effects

Abstract

AbstractThe alkylation of catechol with (chloromethyl)styrene–divinylbenzene copolymer 1 produces the polymer‐bound catechol 2, which upon reaction with a series of polyglycol dihalides affords macrocyclic polymeric benzo crown ethers 3, in fair yields. The alkylation of polybenzylamine 4 with polyglycol dihalides leads to diazapolymeric pseudocrown ethers 5. The degree of conversion of the catechol groups into macrocyclic ether groups and the residual concentration of diol groups were estimated from elemental analysis, weight‐gain data, and the analysis of bis‐2,4‐dinitrophenyl derivatives of the residual diol groups. The ion‐coordination patterns for the polymeric crowns were determined using distribution and column techniques. Equilibrium distribution values in methanol in the temperature range 20–60°C, for the perchlorate, thiocyanate, or bromide salts, have led to the following conclusions: (1) The spheric recognition patterns, typical of crown ethers in solution, are fully reproduced in the polymeric analogs. (2) The order of binding constants is K > Cs > Na > Li for polymeric benzocrown‐6 (3Hc) and benzocrown‐8 (3Hd) and K > Cs ≅ Na > Li for polymeric benzocrown‐4 (3Ha) and benzocrown‐5 (3Hb). (3) The polymers bind alkali metal cations by two mechanisms: the residual diol groups by ion exchange mechanism, and the crown groups by a salt‐coordination mechanism; the second mechanism is temperature‐dependent. Consequently, a thermal increase of 40°C causes a spontaneous elution, by “thermal shock,” and a three‐fold increase in the eluent of the original ion concentration. (4) Quantitative release of all the bound salt is observed.