ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A conductometric method is developed for the study of the ternary solutions in tetrahydrofuran of bis(polystyryl)magnesium (PStMgPSt) containing various proportions r of magnesium bromide. The concentration of bis(polystyryl)magnesium varies from 10-4 to 2.10-3 mol.dm-3, the ratio r from O to 17,4 and the temperature from +20°C down to -60°C. The addition of MgBr2 provokes the replacement of the ion pairs PStMgPSt by PStMgBr, the dismutation constant being at 20°C Kdism = 42 ± 2 with a molar enthalpy of - 5 ± 2 kJ.mol-1. The dismutation is chiefly ruled by a conjugated steric effect that lowers the stability of PStMgPSt. In this concentration range, aggregation of styryl ion pairs is negligible. Moreover for a given r the degree of dissociation of the polymer is independent of its concentration. This is due to the complete predominance in this concentration range of the triple anions Mg(PSt)3-, MgBr(PSt)3- and MgBr2PSt-, approximately in the proportions of the ion pairs fpp, fbp and fbb as calculated from the dismutation constant. The triple anions MgBr3- are still completely negligible, as are also the triple cations. The single cations MgPSt+ and MgBr+ are approximately in the proportion fpp. Kdism/fbp, the latter are ones becoming predominant above r = 3.
Zusätzliches Material:
3 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1993.021941103
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