ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
In the polymerization of oxepane (OXP), initiated with derivatives of trifluoromethanesulfonic acid, covalent and ionic active centers were simultaneously observed by 1H and 19F NMR spectroscopy. A higher proportion of secondary oxonium ions (these species detected by 19F NMR were independently observed by proton trapping with R3P in the 31P NMR spectrum). The proportion of ionic species decreases with monomer conversion, indicating a substantial contribution of bimolecular ionization of the monomer. The effective molarity in oxepane polymerization [OXP]eff ⋍ 1 mol ·I-1 was found to be lower by a factor of 102 than [THF]eff in the polymerization of THF. The rate constant of the covalent propagation in the polymerization of OXP is similar to that measured for THF, however, due to the reduced reactivity of the oxepanium cation, the relative reactivity of the covalent active centers becomes higher than that of the ions. Thus, for OXP, in CH3NO2 at 25°C, Kpc = 3 · 10-4 mol-1 · 1 · s-1, kpi = 2 · 10-4 mol-1 · 1 · s-1 whereas for THF kpc = 5 · 10-4 mol-1 · 1 · s-1 and kpi = 2 · 10-2 mol-1 · 1 · s-1 under similar conditions. The rates of ionization and temporary termination, measured by the “temperature jump” technique, allow to determine the contributions of inter-and intramolecular ionizations. These rates becomes equal at [OXP] = 1 mol · 1-1 (= [OXP]eff).
Additional Material:
10 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1983.021841211
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