AbStlWt
Alkylammonium ions are extractable by polyether-and polyester-type polyurethane foams from aqueous solution in the presence of bulky and hydrophobic anions such as tetraphenylborate (TPB-) and dipicrylaminate (DPA-1. The selectivity for the alkylammonium ions is affected by a combination of effects including steric and inductive effects and hydrophobic interaction. The extractability sequences of NH: > tert-butylammonium > isopropylammonium > ethylammonium > methylammonium for the extraction with polyether foam and reti-butylammonium = isopropylammonium > NH; > ethylammonium > methylammonium for the extraction with polyester foam suggest that there may be some steric hinderance effect for the extraction with polyether foam and the cation chelation mechanism may be predominant. However, these results can also be explained by the weaker hydrogen bonding with polyester foam which gives rise to increasing extraction of isopropylammonium and teti-butylammonium through hydrophobic interaction relative to NH, .
- Therefore, there is no conclusive evidence for the cation chelation mechanism occurring for the extraction with polyether foam.