Thermal stability of polydimethylsiloxane. I. Deactivation of basic active centers

The thermal stability of polydimethylsiloxane is determined by both the resistance of the siloxane chain to depolymerization and the resistance of the hydrocarbon side groups to various forms of degradation. Basic and acidic impurities present in the polymer promote depolymerization as well as degradation. Especially efficient in decreasing the thermal stability are the centers remaining “alive” in the polymer after completed polymerization. The rates of depolymerization and degradation of unstabilized polydimethylsiloxane were measured and compared with those of polymers with active centers deactivated through the formation of complexes with CO 2 and iodine. Also measured was the stability of a polymer prepared by using Bu 4 P(OH) as catalyst and containing only decomposition products of active centers. Inasmuch as high molecular weight polydimethylsiloxanes are seldom used alone, the authors have studied the ability of some oxides (commonly used as fillers) to form complexes with basic active centers and so to influence the thermal stability of polydimethylsiloxane.