Abstract
A kinetic study of the catalyzed reaction between toluene diisocyanate (TDI) and polypropylene glycol (PPG) was carried out in the bulk state by using quantitative Fourier transform infrared (FTIR) spectroscopy. The polymerization was studied in the presence of the catalysts dibutyltin dilaurate (DBTDL) and ferric acetylacetonate (FeAA) at three different temperatures. The kinetics was shown to obey a second-order scheme and the rate plots showed a distinct break in continuity, due to diferent reactivities of NCO groups. It was concluded that the appearance of this break point is related to the use of catalyst as well as type of polyol. The rate constants (k 1 , k 2 ) and the activation parameters (E a1 , E a2 , ΔS 1 #, ΔS 2 #) for the isocyanate groups in the para and ortho positions in TDI molecule were calculated. It was found that the reactivity of p-NCO is 5 to 8 fold higher than o-NCO. The temperature enhances the reactivity of o-NCO rather than the p-NCO. It was also concluded that the FeAA is more sensitive than DBTDL to temperature and is more selective to enhance the reactivity of the o-NCO.
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