EFFECT OF STANNOUS 2-ETHYLHEXANOATE ON THE NETWORK FORMATION AND CHAIN EXTENSION REACTIONS OF ALPHA,OMEGA-DIHYDROXY TERMINATED POLY(DIMETHYLSILOXANE)

α,ω-Dihydroxy terminated poly(dimethylsiloxane) (PDMS) may undergo condensation with multifunctional crosslinking agents such as tetraethoxysilane (TEOS) to give networks having well defined structures, i.e. "model networks". The curing reactions are typically carried out at 298 K by utilizing stannous 2-ethylhexanoate to catalyse the condensation. The present study shows that, at concentrations of 1.0 and 1.5 wt%, the stannous 2-ethylhexanoate promotes significant chain extension of the PDMS in the absence of the crosslinking agent at 293 K. For catalyst concentrations typically used for the preparation of model networks (c < 0.1 wt%), however, no significant chain extension was observed of the PDMS. Furthermore, the results obtained for the curing of α,ω-dihydroxy terminated PDMS with TEOS at 293 K, as catalysed by 0.1 wt% stannous 2-ethylhexanoate, demonstrate that chain extension prior to, or concurrent with, the reaction of functionally terminated chains with the network junctions is insignificant for these conditions. © 1990.