Zum Mechanismus der thermischen Abspaltung von Chlorwasserstoff aus Polyvinylchlorid. 10. Mitt.:. Bestimmung des doppelbindungsgehaltes in polyvinylchlorid durch oxydative kettenspaltung

Abstract

ZUSAMMENFASSUNG :Zur Bestimmung von ungesiittigten Strukturen innerhalb der PolyvinylchloridMakromolekule eignet sich die Oxidation mit Kaliumpermanganat. Bei der Spaltung der Doppelbindungen in den Polyvinylchloridketten mit Kaliumpermanganat tzitt eine merkliche Erniedrigung des Molekulargewichts der Polymeren ein.Reaktionsverlauf und Temperaturabhiingigkeit der Reaktion werden in N.N-Dimethylacetamid als Losungsmittel untersucht. Die Aktivierungsenergie der Oxidationsreaktion ergibt sich aus der Temperaturabhiingigkeit zu 23,9 kcal/Mol. Der Vergleich der Molekulargewichte der untersuchten Polyvinylchloride vor und nach der Oxidation liefert ein Ma13 fur den Doppelbindungsgehalt der Proben. Fur die meisten untersuchten Polymeren wurden Gehalte von 0,2 bis 1,2 kettenstiindigen Doppelbindungen pro 1 000 Kohlenstoff-Atome gefunden. SUMMARY:For determination of random unsaturation within the macromolecules of polyvinyl chloride the oxidation of double bonds by potassium pennanganate is used. After the cleavage of the polymer with potassium pennanganate a remarkable decrease in molecular weight is observed.The oxidation reaction was investigated using N.N-dimethylacetamide as a solvent. From the temperature dependence of the reaction rate an activation energy of 23,9 kaal/mole is calculated. A comparison of the molecular weights before and after oxidation gives the average content of double bonds within different samples, which was found for the products under investigation from 0.2 to 1.2 double bonds per 1000 carbon atoms by this method.

Thermal stabilisation of PVC with metal soaps of Khaya seed oil

“…At elevated temperatures, well below its decomposition temperature, PVC loses HCl, and becomes discoloured, leading to changes in chemical and physical properties of the polymer. Thermal degradation of PVC is generally considered to be initiated at unstable structural irregularities (particularly tertiary and allylic chlorides) within PVC, and some authors [1][2][3][4][5] have claimed that these structural defects are responsible for the low thermal stability of the polymer. Although structural irregularities considerably increase the initial rate of PVC degradation, and indeed initial rates of degradation at low conversions (0.1 -0.3%) have been shown to correlate well with allylic and/or tertiary chloride content of PVC 6,7) , it has been argued that on account of the low concentrations in normal PVC of these structural irregularities, initiation of thermal degradation of PVC also takes place at regular monometric units [8][9][10][11][12] .…”

“…Although structural irregularities considerably increase the initial rate of PVC degradation, and indeed initial rates of degradation at low conversions (0.1 -0.3%) have been shown to correlate well with allylic and/or tertiary chloride content of PVC 6,7) , it has been argued that on account of the low concentrations in normal PVC of these structural irregularities, initiation of thermal degradation of PVC also takes place at regular monometric units [8][9][10][11][12] . In addition to the difficulties in identification and quantification of such small amounts of labile allylic and tertiary chlorides within the normal PVC structure (with implications for accurate assessment of their effects on degradation), it is difficult to separate their effects on degradation from that of normal polymer units [1][2][3][4][5]13) . It is now generally well accepted that random elimination of HCl from regular monomer sequences is responsible for the higher degree of degradation conversion 14) .…”

Thermal analysis in studies of photochemical transformations in PVC

“…A decrease in the temperature of dehydrochlorination is caUsed by fragments of polymer resulting from head-to-head linkages [1,2]. A negative effect on the thermal stability of this polymer is exerted by unsaturated intramolecular bonds, fl-chloroalkyl groups, double bonds at the chain ends, and groups containing oxygen atoms [10][11][12][13][14][15][16][17]. This is particularly so for branches with chlorine atoms at tertiary carbon atoms [5,6].…”