Insight into the mechanism of the catalysis of urethane formation by organotin(IV) dicarboxylate
The field of surface coatings is an area of urethane technology and is rapidly gaining popularity due to ongoing performance improvements. Key to this is improved control of the catalysis of the urethane reaction obtained through an increased understanding of the catalysis mechanisms involved. Organotin dicarboxylates are industrially important catalysts in the formation of urethanes by reacting an isocyanate with an alcohol. This catalyst works for both aliphatic and aromatic isocyanates; however in industrial applications the catalyst is less important for aromatic isocyanates than aliphatic isocyanates. It has already been shown from our earlier investigations of catalysis mechanisms that organotin dicarboxylate catalysis of aromatic isocyanates is different to the mechanism for aliphatic isocyanates for urethane formation in non-polar media. In the present study, we further confirm these results using thermochemical data, which show that for organotin dicarboxylate catalysis of isocyanates in non-polar media, the carboxylate ligand of the catalyst contributes to catalysis of aliphatic isocyanates whereas the ligand has no effect for catalysis of aromatic isocyanates. The new knowledge was used to explain the behavior of pre-polymer when synthesized using different organotin compounds as catalyst with respect to viscosity increase in storage. These data will be useful in the manufacture of pre-polymers for 1 component (1 K) moisture cure urethane systems.
KeywordsOrganotin dicarboxylate Computational modelling Isocyanate Urethane Catalyst
The authors thank Uroxsys Ltd. for financial support and the publication referees for their valuable advice. They also thank the New Zealand eScience Infrastruture (NeSI) for providing high performance computing facility to carry out the computational work, the University of Auckland for providing access to the HPC facilities and the technical support teams at Gaussian and Wavefunction for their valuable help.
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