Thermal degradation of polymethacrylonitrile. IV. Formation and decomposition of ketene-imine structures

Autor: N. Grassie, I. C. McNeill
Rok vydání: 1958
Předmět:
Zdroj: Journal of Polymer Science. 33:171-182
ISSN: 1542-6238
0022-3832
DOI: 10.1002/pol.1958.1203312617
Popis: The reaction of ketene-imine structures in polymethacrylonitrile is most conveniently followed by observing the disappearance of the 2012 cm.−1 peak in the infrared spectrum. These structures are stable to 120°C. in the bulk material but disappear rapidly in solution at lower temperatures. Like simple ketene-imines they are destroyed by addition of water, chlorine, methanol, and hydrogen sulfide. Thermal decomposition in cyclohexanone solution in the temperature range 65–90°C. is a second-order process. The second-order rate constant decreases with increasing polymer concentration although, within experimental error, it is independent of the ketene-imine concentration. The rate constant can also be depressed by addition of polymethyl methacrylate. These observations have been interpreted in terms of diffusion (viscosity) control of the reaction rate. Ketene-imine structures are formed during polymerization by reaction of the growing polymer radical in the form By preparing a series of polymers at the same temperature (30°C.) but with different initiator concentrations and determining their ketene-imine contents, it has been possible to show that the ketene-imine structures are formed predominantly in the termination step. The ketene-imine form of the radical appears not to be reactive enough to add monomer readily in a propagation process. The mechanism of the thermal disappearance of ketene-imine structures is not clear. In particular it is difficult to correlate the second-order kinetics with the chain-scission process which is associated with the reaction. There is some evidence, however, that the extent of this chain scission is a measure of ketene-imine concentration.
Databáze: OpenAIRE
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