AIR ACTIVATED ORGANOTIN CATALYSTS FOR SILICONE CURING AND POLYURETHANE PREPARATION

Upon exposure to air, 1,2-bis(acyloxy)tetraalkyldistannanes incorporat ed in mixtures of either silicone oils and curing agent, or of isocyan ates and alcohols, are oxidized to 1,3-bis(acyloxy)tetraalkyldistannox anes which show excellent catalytic properties for curing silicones or for preparing polyurethanes. Under nitrogen, they induce longer pot-l ives than the usual bis(acyloxy)dialkylstannane catalysts. Peralkyl-po lycyclostannanes, obtained either by the palladium-catalyzed decomposi tion of dialkylstannanes or by reduction of dichlorodialkylstannanes w ith metals, are also very good latent catalysts for silicone curing. W hen incorporated into reactive mixtures under nitrogen, they do not ca talyze the condensation. Upon exposure to air, they are oxidized to ac tive catalysts which cure silicones. These di- or polystannanes can be considered air-activated latent organotin catalysts.