Effect of the carboxylate salt on the C--ON bond homolysis of SG1-based alkoxyamines.
Alkoxyamines and persistent nitroxides are important regulators of the nitroxide mediated radical polymerization (NMP). Since the polymerization time decreases with increasing values of the homolysis rate constant (kd) for the C--ON bond between the polymer chain and the nitroxide moiety, the factors influencing kd are of considerable interest. Environmentally friendly polymerization methods, such as NMP in emulsion medium, have now been developed. The success of the polymerization depends not only on the strength of the C--ON bond but also on the solubility of the initiator/controller alkoxyamines, which control the nucleation. Various salts of SG1-based alkoxyamines (S+-OOCCMeH-SG1) labelled 1 a-f, where S+=Li+ (a), Na+ (b), K+ (c), nBu3HN+ (d), NH4+ (e), and nBu4N+ (f) are prepared, all of which are soluble in most organic solvents (e.g. pentane, dichlomethane, benzene, ethanol, etc.) as well as in water. Their kd values, which are measured in tert-butylbenzene, reveal unexpected behaviors depending on the diastereoisomers. For the RR/SS diatereoisomers (i.e. slowly homolyzing isomers), kd was not found to be sensitive to any of the salts, whereas for the RS/SR diastereoisomers (i.e. quickly homolyzing isomers), kd is observed to decrease to a greater or lesser extent depending on the type of salt. The conformations of the diastereoisomers of several salts are determined by means of DFT calculations, and the orbital interactions are studied by natural bond orbital (NBO) analysis.
Bertin
Denis
D
UMR 6517 case 521, Aix-Marseille Université, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France.
Gigmes
Didier
D
Marque
Sylvain R A
SR
Siri
Didier
D
Tordo
Paul
P
Trappo
Gregory
G
D000588:Amines / Q000138:chemical synthesis / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D015394:Molecular Structure; D063065:Organophosphonates / Q000737:chemistry*; D011789:Quantum Theory; D012492:Salts / Q000737:chemistry; D012995:Solubility; D012997:Solvents / Q000737:chemistry; D013237:Stereoisomerism
D000588:Amines; D002264:Carboxylic Acids; D005609:Free Radicals; C527815:N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl; D063065:Organophosphonates; D012492:Salts; D012997:Solvents