Abstract: The heat-stabilizing effect of several dialkyltin dicarboxylates on poly(vinyl chloride) (PVC) was investigated by an oven discoloration method. The results indicated that the heat-stabilizing function of dialkyltin dicarboxylates toward PVC was improved with an increase of the positive electricity of carbonyl carbon atom in their carboxylate groups. If there were dienophilic structural units in the molecules of dialkyltin dicarboxylates, the discoloring test specimens of PVC stabilized with them showed a lighter color until the specimens were blackened finally. On the basis of the molecular structural characteristics of dialkyltin dicarboxylates as well as the gradually varying regularity of thermal stability for PVC stabilized with them, the stabilization mechanisms are attributed to the electrophilic reaction with PVC through the carbonyl carbon atoms of dialkyltin dicarboxylates and/or dialkyltin ions as a electrophilic center (referred to electrophilic reaction mechanism). If there are dienophilic structural units in the molecule, PVC is stabilized with dialkyltin dicarboxylates in terms of the electrophilic reaction and Diels-Alder reaction mechanisms synchronously. The former plays a primary role and the latter acts as the auxiliaryone.

Key words: organotin dicarboxylate, poly（vinyl chloride）, heat stabilizer, progressive change law, mechanism