Hamon R F, Khan A S, Chow A
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, Canada.
Talanta. 1982 Apr;29(4):313-26. doi: 10.1016/0039-9140(82)80118-5.
The mechanism of sorption of ions by polyurethanes has been investigated through detailed studies of the extraction of cobalt(II) thiocyanate and the salts of several organic acids. Polyether-based polyurethanes. particularly those containing poly(ethylene oxide), were found to be distinctly superior to polyesters in the sorption of salts and performed much better than might be expected by analogy with monomeric liquid solvents. The results were judged to be inconsistent with several possible mechanisms, including adsorption, solvent extraction, weak or strong base anion-exchange, and complexation of metal anions by the polymer. A new proposal, termed the cation chelation mechanism (CCM), was advanced to account for the observations. In this view, a number of cations (including those of the alkali metals, alkaline earth metals, some transition metals, NH(+)(4), RNH(+)(3) and perhaps H(3)O(+)) may be multiply complexed (chelated) by portions of the polymer, thus facilitating the sorption of accompanying anions. As predicted by the mechanism, moderately strong and selective complexation of several cations was observed to occur with the following order of selectivity: Li(+) < Na(+) < Cs(+) < Rb(+) < K(+) approximately NH(+)(4) < Ag(+) approximately Tl(+) < Ba(2+) < Hg(2+) < Pb(2+). Such behaviour parallels that known for many crown and non-cyclic polyethers and is therefore identified with the polyether portions of the polymer, which are thought to adopt helical conformations surrounding the complexed cations. The cation-chelation mechanism may be widely applicable to the sorption of ions of several types by polyether-based polyurethanes, particularly when large, hydrophobic anions (such as anionic metal complexes) are accompanied by an excess of chelatable cations.
通过对硫氰酸钴（II）和几种有机酸的盐的萃取进行详细研究，对聚氨酯吸附离子的机制进行了探究。发现聚醚基聚氨酯，特别是那些含有聚环氧乙烷的聚氨酯，在盐的吸附方面明显优于聚酯，并且其表现比通过与单体液体溶剂类比所预期的要好得多。结果被判定与几种可能的机制不一致，包括吸附、溶剂萃取、弱碱或强碱阴离子交换以及聚合物对金属阴离子的络合。提出了一种新的提议，称为阳离子螯合机制（CCM），以解释这些观察结果。按照这种观点，许多阳离子（包括碱金属、碱土金属、一些过渡金属、NH₄⁺、RNH₃⁺以及可能的H₃O⁺）可能会被聚合物的部分基团多次络合（螯合），从而促进伴随阴离子的吸附。正如该机制所预测的，观察到几种阳离子发生了中等强度和选择性的络合，其选择性顺序如下：Li⁺ < Na⁺ < Cs⁺ < Rb⁺ < K⁺ ≈ NH₄⁺ < Ag⁺ ≈ Tl⁺ < Ba²⁺ < Hg²⁺ < Pb²⁺。这种行为与许多冠醚和非环状聚醚所已知的行为相似，因此被认为与聚合物的聚醚部分有关，据认为这些聚醚部分会围绕络合的阳离子采取螺旋构象。阳离子螯合机制可能广泛适用于聚醚基聚氨酯对几种类型离子的吸附，特别是当大的疏水性阴离子（如阴离子金属络合物）伴有过量的可螯合阳离子时。
