Etude de la stabilisation du polychlorure de vinyle avec des composes modeles—III. Action des stearates de zinc et de calcium

Esterification of chloro-4-hexene-2 with zinc stearate in tetrahydrofuran at 60° is a moderate reaction, strongly catalysed by zinc chloride. That catalyst is necessary in the case of calcium stearate. The synergistic effect between the two reactants cannot be explained first by the exchange reaction between zinc chloride and calcium stearate; that reaction is reversible and limited. A better explanation is based on the formation of complexes between both stearates, or both chlorides, or eventually between zinc chloride and calcium stearate. The catalytic activity of zinc chloride in these complexes is decreased or even inhibited. There is no true synergistic effect between aliphatic phosphites and zinc stearate at 60° in THF. There is only catalysis of allylic chlorine substitution by a phosphonate group by the zinc chloride produced in the reaction. In dichloroethane at 60°, each of the two stearates has a stabilizing effect, although by different mechanisms, zinc stearate being more active; the zinc chloride which is formed is a catalyst, in the presence of hydrochloric acid, for hexadiene oligomerization. Transposition of the previous results to the polymer has been carried out by using a Brabender plastograph. A direct correlation has been obtained concerning the efficiency of mixtures of the two stearates versus the dehydrochlorination and the crosslinking reactions.