The thermal degradation of polyvinylchloride in solution. II. The kinetics of the crosslinking reaction

Abstract

The cross-linking of polyvinylchloride in ethyl benzoate solution has been studied over the temperature range 178 to 212°C. in an atmosphere of nitrogen. The effects of variation in polymer concentration and in molecular weight of the polymer on the time taken for the polymer solution to gel have been observed, and the rate of crosslinking has been calculated from such data by applying FLORY'S theory of gelation. Over the above-mentioned temperature range the expression for the rate of crossbond formation was found to be 2.0.103 e-23,000/RTci crossbonds/l:sec., where c w is the polymer concentration in monomoles /l. This expression applies to polymer samples with number average degrees of polymerization varying from 192 to 905, and may well apply to an even wider range.The addition of free radical initiators and free radical inhibitors had little effect on the time of gelation whereas oxygen retarded or prevented gel formation. The results in general support the view that the crosslinking process proceeds by a non-radical mechanism, and involves a random condensation reaction between two structural units in different polymer molecules with the elimination of HCI. ZUSAMMENFASSUNG:Die Vernetzung von Polyvinylchlorid wurde in Benzoesaureathylester-Losung unter Stickstoffatmosphire im Temperaturbereich 178 bis 212°C untersucht. Die in Abhangigkeit von der Konzentration und dem Molekulargewicht des Polymeren beobachtete Zeit, bis Gelierung auftrat, diente zur Berechnung der Vernetzungsgeschwindigkeit nach der FLoRYschen Gelierungstheorie. Danach ist innerhalb des angefuhrten Temperatubereiches die Geschwindigkeit der Vernetzungsbriickenbildung 2,0.103. e-23000/RT.ci Vernetzungsbriicken/l.sec, wobei c, die Polymerkonzentration in Monomolen/Z bedeutet. Dies gilt fur Polymere mit dem Zahlenmittel des Polymerisationsgrades 192 bis 905 und ist vermutlich auch auf3erhalb dieses Bereiches gultig.Zugesetzte freie radikalische Initiatoren und freie radikalische Inhibitoren hatten eine geringe Wirkung auf die Gelierungszeit, wahrend Sauerstoff die Gelbildung verzogerte oder verhinderte. Die Ergebriisse weisen im allgemeinen auf einen nicht radikalischen Mechanismus beim Vernetzungsvorgang hin und lassen sich durch eine zufallige, mit einer HCl-Abspaltung verbundenen Kondensation zwischen zwei Struktureinheiten verschiedener Polymermolekeln erklaren.

Principles of Thermal Degradation

“…178,184,185 According to Gupta,178 crosslinking started in the presence of oxygen after three hours of degradation at 463K, while in inert gas, the sample already contained 53% crosslinked material. 178,184,185 According to Gupta,178 crosslinking started in the presence of oxygen after three hours of degradation at 463K, while in inert gas, the sample already contained 53% crosslinked material.…”

Increase of PVC thermal stability through chemical modification by dibutylester of malein acid

“…To reduce the probability of intermolecular reaction it is necessary to work in solution. The beginning of PVC gel formation depends to a considerable degree on the concentration (13). The presence of oxygen causes the breaking of chains (14), but it may also lead to the formation of nonstable groups in split-off polymer.…”

Kinetic studies on the telomerization and polymerization of vinyl chloride

“…The termhation step involves the interaction of trichloromethyl radicals, for which the velocity coefficient at 25°C was 2.2 and 4 3 x 108 depending upon the data used for rate of initiation. 6 kcal/mole depending upon the products of the reaction were found using the dilatometric method. 8 x lo9 1.…”

“…4 to 27. 6 kcal/mole depending upon the products of the reaction were found using the dilatometric method.…”

“…They deduced that under conditions such that reaction (2) is the slow step in the propagation process (e.g., with excess TBr) termination proceeds mainly via reaction (4), and the rate of reaction is then given by -dM/d t = k2(l/k4)0* 5 [MI, (i) where I is the rate of initiation. Again when reaction (3) is rate controlling, termination occurs mainly by reaction (6) and the rate is given by -dM/dt = k3(I/k@*5[TBr].…”