The Effects of Organotin Catalysts on Hydrolytic Condensation of Polymethylsiloxane Oligomer and Moisture Cure of the Coatings

Abstract

The Polymethylsiloxane oligomer (P-MTS) was synthesized by the hydrolytic condensation of trimethoxy (methyl) silane. The effect of mono-and bis-type organotin carboxylate catalysts on hydrolytic condensation of P-MTS was investigated in relation to pot life time and tack free time of P-MTS coating in the presence of catalysts. The viscosity variations and tack free time of P-MTS on aging were measured with IR and NMR spectral analysis. It was observed that the condensation reaction proceeds faster with bis-type catalysts than mono-types depending on the concentration of active species generated from the hydrolysis of the organotin catalysts. On the other hand, the tack free time was found to be correlated with the functional group of organotin carboxylates. Due to the steric hindrance of the functional group, dibutyltindilaurate is less easily hydrolyzed to the inactive dibutyltinoxide compared to dibutyltindiacetate. This results in the lauroyloxy group taking part more effectively in catalytic action than the acetoxy group. From these results, it was revealed that the structure of organotin catalysts plays an important role on the condensation of the P-MTS and the cure of its coating.