The chemistry of poly(vinyl chloride) stabilization. IV. Organotin stabilizers having radioactively tagged tin atoms

Abstract

AbstractThe chemistry of poly(vinyl chloride) stabilization by organotin compounds has been studied by the use of a radioactive tracer technique. The stabilizers studied were of the type [R2Sn Y2]n, where R was either butyl or octyl, Y either monomethyl maleate, oxooctylthioglycolate, or β‐mercaptopropanoate, and 113Sn was the radioactive tag. It was found that resins milled into films with the tagged stabilizers retain an appreciable amount of radioactivity after the films have been subjected to the conditions of accelerated thermal degradation, dissolution in tetrahydrofuran, and thereafter precipitated from solution by the addition of methanol. The amount of retained radioactivity varies with the duration of the heat treatment and with the nature of the Y group in a manner that parallels our findings in a previously reported study using a 14C tag in the stabilizers' butyl groups. We have also found that the amount of radioactivity retained by the precipitated resins decreases in a regular manner when the resins are subjected to a sequence of repeated dissolutions and precipitations. However, in the case of the resin stabilized with dibutyltin‐113Sn bis(monomethyl maleate) at least, the loss of radioactivity with repeated dissolution and precipitation appears to level off after 13–14 cycles and approach a constant value of retention. Treatment of the radioactive resins with anhydrous hydrogen chloride results in the loss of essentially all their radioactivity. On the basis of these findings, we suggest that in the performance of their stabilizing action, the organotin compounds undergo little or no cleavage of their carbon‐tin bonds. Further, the observed retention of radioactivity by the resin is best rationalized as due to the existence of a coordinative linkage formed between the stabilizer's tin atom and some donor atom present in polymer's molecular structure.