ISSN:
0959-8103
Keywords:
dehalogenative step polymerization
;
nickel catalyst
;
kinetics
;
reaction mechanism
;
poly(N-alkylcarbazolylene)s
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Dehalogenative polycondensation of 3,6-dibromo-N-alkylcarbazoles was catalysed by a Ni(O)-based complex generated in N,N-dimethylacetamide by electroreduction of NiBr2/2,2′-bipyridine. The process involves three different reaction steps, which are successively: electrolysis of Ni(II) to Ni(O); insertion of the latter into a C—Br bond of monomer leading to C—Ni—Br* active species; dehalogenative coupling between active species and monomer yielding oligomers. From the kinetics of electrogeneration of the catalytic system in absence of monomer, a first-order reaction was determined. Insertion and coupling reactions were found to be second-order and comparison of the values of the corresponding rate constants clearly showed that coupling is the rate-determining step of the process. Simultaneous size exclusion chromatography and cyclic voltammetry measurements were carried out in the course of the electrosynthesis of poly(N-alkylcarbazole)s. The change in the molar mass population distribution as a function of electrolysis time revealed a step polymerization process, while showing a termination of the chain growth due to the occurrence of monobrominated species. The study of the effect of the [monomer]/[catalyst] ratio on the molar mass population change indicated that the coupling of active species (Ni(O)-activated monomer) is responsible for the chain growth.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pi.1995.210370304
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