THE USE OF ORGANOTIN COMPOUNDS IN THE THERMAL STABILIZATION OF POLYVINYL-CHLORIDE) .6. AN ASSESSMENT OF THE RELATIVE IMPORTANCE OF HCL-SCAVENGING, EXCHANGE, AND ADDITION-REACTIONS

In the reported experiments, reactions of PVC with three representative stabilizers Bu//2SnY//2 (Y equals OCOC//1//1H//2//3, SCH//2COOCH//2CH(Et)CH//2CH//2CH//2CH//3, OCOCH equals CHCOOMe) in solution and under nitrogen were studied by two principal methods. First, using stabilizers with radioactive labels in the Y groups, the uptake of these groups by virgin and degraded polymer was measured. The UV-visible absorption spectra of the stabilized polymers are discussed. Second, the effect of these three stabilizers on the rate of elimination of hydrogen chloride from heated PVC was studied. It is shown that the effects of HCl-scavenging and of exchange reactions in suppressing the evolution of HCl can be separately evaluated. The thermal decomposition of dibutyltin bis(methyl maleate) to give maleic anhydride is reported. Interpretation of the observations is made in terms of assessing the relative importance of the various polymer-stabilizer reactions in promoting stabilization.