The chemistry of poly(vinyl chloride) stabilization. III. Organotin stabilizers having radioactively tagged alkyl groups

Abstract

AbstractThe stabilizing action of a representative group of organotin compounds of the formula Bu2Sn Y2 has been studied by a radioactive tracer technique, the tags (14C) being located in the butyl group's C1‐position. The Y groups of the chosen organotin compounds were: monomethyl maleate, oxoöctyl thioglycolate, β‐mercaptopropanoate, and 2‐ethylhexanoate. It was found that after a sequence of two dissolution and precipitation cycles (using tetrahydrofuran and methanol) an appreciable portion of radioactivity is retained by the resin, the resins having been previously admixed with the tagged stabilizer, milled into films and then subjected to carefully controlled heat treatments. Under these conditions it was found that the amount of radioactivity retained by the resin was determined by the nature of the Y group and the duration of the heat treatment. Further, it was found that for a given Y group, the amount of retention first increases with increase in the duration of the heat treatment, reaches a maximum, and then drops off. However, the amount of radioactivity retained by such a resin was not found to be constant when the sample was subjected to further dissolution–precipitation cycles, but, within the limits of the present experiments, to decrease markedly with each successive cycle. It is suggested that the major portion of this retention is due to the formation of an associative link between the polymer and the organotin compound and that this linkage is partially ruptured by the tetrahydrofuran–methanol treatment. It is also shown that only a very minor portion of the radioactivity retained by the precipitated resin can be due to actual butylation of the resin as preposed by Kenyon, and that it is unlikely that it could contribute appreciably to the resin's stabilization. It is suggested that the formation of an associative complex between the resin and the organotin compound functions as a precursor wherein certain relatively labile centers in the polymer chain can be altered, possibly by a displacement reaction involving the organotin compound's Y group, and int his way retard or inhibit the zipperlike elimination of hydrogen chloride which is the initial phase of the polymer's degradation.