No abstract

High molecular weight nonionic surfactants have been chemically modified to bind multivalent ions reversibly by using a moderate temperature stimulus as an on/off mechanism. Only above the critical micellization temperature (CMT) does binding of multivalent ions take place, whereas below the CMT, no binding occurs to the free surfactant molecules. Different calorimetric techniques have been used to prove the reversible binding of multivalent ions. This tunable binding of multivalent metal ions allows for the improvement of many ion-exchange processes and offers attractive opportunities in the biomedical field.

Eight (15)N-labeled derivatives of 1-ethoxy-2,2,6,6-tetramethylpiperidine were synthesized in order to investigate the effects of their structural units on (15)N NMR spectra. A single peak is found for each alkoxyamine. The chemical shift depends extensively on the nature of the alpha carbon atom of the alkoxy group. The remote functional group attached to position 4 of the piperidine ring has a smaller but still significant effect. The results of the (15)N NMR measurements are supported by the detection of the N-H and N-C spin-spin coupling from the (1)H and (13)C NMR. The investigated alkoxyamines are model compounds for the radical-trapping products of styryl, methyl methacryloyl, alpha-methylstyryl, and methyl acryloyl radicals by (15)N-labeled nitroxides. The potential of (15)N NMR spectroscopy to analyze such products is discussed. In addition, it is shown that the (13)C chemical shifts of the alpha carbon atom of the alkoxy group fall in an empty part of the (13)C NMR spectrum, which allows the identification of trapped (macro)radicals via natural abundance (13)C NMR.

15 N-labeled nitroxides are employed to trap propagating radicals in the copolymerization of styrene and methyl acrylate. The resulting polymeric alkoxyamines are analyzed by 15 N NMR. The assignment of the observed bands to the two possible end groups of the propagating copolymer chain is achieved by comparison of the spectra with the homopolymer alkoxyamines. Copolymers in the suitable molar mass range for the current investigation are obtained by the formation of initiating radicals and nitroxyl radical traps in situ, from a low molar mass 15 N-labeled alkoxyamine.