The effect of some additives on the thermal degradation of poly(methyl methacrylate)
The thermal degradation of poly(methyl methacrylate), (PMMA), has been studied in the presence of five tin additives (phenyltin trichloride, diphenyltin dichloride, triphenyltin chloride, tin(IV) chloride, tetraphenyltin), five transition metal chlorides (nickel(II) chloride, copper(I) chloride, copper(II) chloride, iron(II) chloride, iron(III) chloride), and diphenyl disulfide. A complete mechanistic interpretation of these reactions is provided. The degradation of three phenyltin chlorides (PhSnCl$\sb3$, Ph$\sb2$SnCl$\sb2$, and Ph$\sb3$SnCl) proceeds by the initial loss of a phenyl radical with the formation of a tin-based radical, these initially formed radicals interact with the polymer. For tin tetrachloride, the initial step is coordination of the SnCl$\sb4$ to the carbonyl oxygens of the polymer followed by the loss of methyl chloride from the coordinated complex. The Limiting Oxygen Index of this blend is very high indicating some potential flame retardant activity for compounds of this type. For the blend of PMMA with tetraphenyltin, the degradation proceeds in a mutually-assisted manner with radicals from one material promoting degradation of the other. The thermal degradation of PMMA in the presence of iron(II) chloride, iron(III) chloride, copper(I) chloride, copper(II) chloride, and nickel(II) chloride has been studied by the combined technique of thermogravimetric analysis coupled to a Fourier transform IR spectrometer. In those cases where coordination occurs between the transition metal ion and the carbonyl oxygens of the polymer, there is an effect on the degradation of the polymer; in those cases where coordination does not occur, the degradation is unaffected by the presence of the additive. The presence of methyl chloride as one of the gases evolved is diagnostic for a coordination; when this gas is absent, the degradation of the PMMA proceeds unaffected by the presence of the transition metal ion. Diphenyl disulfide has shown some stabilizing effect on the thermal degradation of PMMA at higher temperatures. Acting as a chain transfer agent, diphenyl disulfide will interact with the macroradicals produced by the polymer and terminate further degradation by producing a high yield of phenylthio-containing oligomer and non-volatile residue. The oxidation of a mixture of thiophenol and methyl methacrylate produces some interesting sulfur compounds, some of them were found in the product mixture of PMMA/PhSSPh reaction. These compounds were separated and identified by the spectroscopic methods and the mechanism for the formation was proposed.
Jayakody A Chandrasiri,
"The effect of some additives on the thermal degradation of poly(methyl methacrylate)"
(January 1, 1994).
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