Organophosphite transformations in flexible PVC formulations

Abstract

Organophosphites are a versatile component of liquid PVC heat stabilizers and stabilize PVC through a variety of mechanisms. Organophosphites can decompose peroxides, replace labile chlorines on the PVC backbone, scavenge HCl (via the Arbuzov rearrangement), complex Lewis acids, and add to double bonds. This paper attempts to identify the relative contributions of these mechanisms in both model systems and flexible PVC formulations.

Principles of Stabilization

“…These studies were more recently confirmed by Jakupca et al 56 who studied oxidation of paraffins at 180 o C in the presence of triphenyl and tri-n-octyl phosphites. Alkyl phosphite was more reactive towards peroxides than aryl phosphite.…”

“…Alkyl phosphite was more reactive towards peroxides than aryl phosphite. 56 It should be noted that although alkyl phosphites are more reactive than aryl phosphites, they are also less hydrolytically stable. 56 Triphenyl phosphite was also converted into triphenyl phosphate, but at a much slower rate compared to alkyl phosphite.…”

“…Tri-n-octyl phosphite was rapidly oxidized to the phosphate. 56 Similar processes in the presence of organotins are more complicated. 56 It should be noted that although alkyl phosphites are more reactive than aryl phosphites, they are also less hydrolytically stable.…”

“…The comparative influence of three phosphites on color changes follows the same pattern as their influence on dehydrochlorination (Figure 11.31) and it also can be explained by the differences in the strength of acids formed in the process of reaction with HCl. 56 The following reaction scheme has been previously proposed: 8 It is agreed that phosphites are also able to replace labile chlorine atoms and thus affect the dehydrochlorination rate, 23,24,56,[286][287][288]295 but disagreement existed concerning the type of group containing labile chlorine atoms that is able to react with phosphite. Figure 11.34 implies that there is a concentration at which zinc stearate is the most effective.…”

“…Figure 11.34 implies that there is a concentration at which zinc stearate is the most effective. This supposition was not generally accepted (similar to influences of the ketochloroallyl group on initiation of dehydrochlorination) and it is commonly agreed now that the following reaction takes place: 19,24,56,286,287,295,296 This reaction was seen to be not very selective because up to 5% phosphorus was found in PVC after intensive dehydrochlorination. Essential to the mechanism of action of phosphite is its ability to react with ZnCl 2 .…”