Model Compounds Studies to Establish the Basic Mechanism for Tin Stabilizers in Polyvinylchloride

Abstract

Among PVC stabilizers the organotin compounds, mainly thioglycolate and maleate derivatives, are enjoying a growing importance. In addition, the best recipe includes a mixture of mono- and dialkyl derivatives, which shows a synergistic effect. It was attempted to compare these systems with the metal soap recipe, which includes a synergistic mixture of barium and cadmium, or calcium and zinc carboxylates. Such a comparison was recently suggested by Burley and Hutton,¹ who showed from infrared evidences that exchange of chlorine with thioglycolate groups occurred between the mono- and dialkyl compounds; so, the formation of dibutyltin dichloride is favored instead of butyltin trichloride, which is more strongly prodegradant than dibutyltin dichloride. The situation may be compared to that of the calcium-zinc system, where the exchange reaction favors the formation of calcium chloride instead of the strongly prodegradant zinc chloride. Other aspects of the mechanisms involved in the zinc calcium recipe have been extensively treated in our previous works.² They deal mostly with the catalytic activity of zinc chloride versus the dehydrochlorination reaction, as well as the substitution reaction and other side reactions.