FTIR investigations on hydrolysis and condensation reactions of alkoxysilane terminated polymers for use in adhesives and sealants

Transmission FTIR was successfully applied to monitor the hydrolysis reaction of an alkoxysilane-terminated polybutadiene model polymer for a selection of catalytic and co-catalytic systems under controlled environmental conditions (23 °C, 50% relative humidity). Monitoring of the condensation reaction of the model polymer via FTIR spectroscopy was limited to qualitative evaluation. The aim of this work was to find a new tin-free alkoxysilane crosslinking catalyst, active at room temperature as an alternative to dibutyltin dilaurate (DBTDL). Hydrolysis rates (k), hydrolysis turn overs, and tack free times were determined for the model system with added water and in the presence of different catalysts, such as DBTDL, diisobutoxy bis(ethylacetoacetato) titanate (Tyzor IBAY), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), boron trifluoride monoethylamine (BF3-MEA) and tris(pentafluorophenyl)borane (BCF) in concentrations of 3 mol%. For BCF a high catalytic activity was observed for both, the alkoxysilane hydrolysis and the condensation reaction. The simultaneous use of BCF and Tyzor IBAY was found to increase hydrolysis reaction׳s turn overs significantly. Thereby a highly efficient co-catalytic system was established, which was found to be active at room temperature showing potential as a new, tin-free alkoxysilane crosslinking catalyst.

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