Catalytic activity of DBTDL in polyurethane formation

Polyurethane has been prepared from neopentyl glycol (NPG) and toluene diisocyanate (TDI) using dibutyltin dilaurate (DBTDL) catalyst. The rates of both the uncatalyzed and catalyzed polyurethane formation reactions were investigated. In case of catalyzed reaction the sequence of addition of catalyst was also investigated and it was observed that the activity of the catalyst is dependent on the sequence of addition of DBTDL catalyst. Titrimetric method was used for the determination of residual isocyanate content. Highest reaction rate was observed when the catalyst was added after the addition of TDI to diol and lowest rate was observed when no catalyst was used. It was observed that when the catalyst was added to NPG followed by TDI addition the rate of reaction was slower compared to that when catalyst was added to the mixture of diol and TDI. 1 H NMR and IR study of the complex formation between the tin catalyst and diol was evaluated to account for the lower reaction rate.