Thermal stability of polydimethylsiloxane. II. Formation of stable complexes on basic active centers

Amphoteric hydroxides are found to possess a great ability to deactivate the “living” ends of polydimethylsiloxane molecules. They not only prevent depolymerization but also suppress the formation of crosslinks between polymer molecules (which is due to the oxidation of methyl groups). Deactivation of active centers can also be carried out by benzoic acid; however, this acid attacks siloxane bonds at elecated temperatures and promotes decreased molecular weight of polydimethylsiloxane. This undesirable decrease in molecular weight is not caused by benzoic acid only in polymers which originally contained basic active centers; it is found also in polymers without any “living” ends, whether these were removed by transformation into stable complexes or decomposed by heating at 150°C. (as in the case of SiOPBu 4 ).