Influence of Silica Modulus on OMC End Product Composition

The end products of the following reaction systems were identified by IR spectroscopy  

Reactions were run at 295 K at 1 1 and 1 3 ratios of NCO OH reactive groups. Reaction product spectra were taken on a JR-75 device in the range of 400-4000 cm at 295 K with specimens in the form of KBr disks. 

It was found that the position and intensity of the IR absorption bands of the products of (l)-(3) were approximately the same. Increase in the initial alkali concentration (to more than 20%) produces changes in the spectra of reaction products of (4)-(6) at 600-1750, 3000-3500, and 2275 cm bands, the intensity of which is noticeably reduced. This indicates that the composition of the products of reaction of 2,4-TDI with alkalis differs for low (up to 20%) and high (more than 20%) concentration of alkali. 

It is known [67] that the reactions below will proceed provided a strong base is available with isocyanate interaction with water  

The relative band intensities in the spectra of the reaction end products (4)-(6) change as alkali concentration is increased the bands at 1550 and 1640 cm develop shoulders the absorption intensity varies around 1620 cm and bands appear at 1320, 1580, 1715, and 1920cm . The 1320 and 1580cm absorption bands are explained by symmetric and asymmetric stretching vibrations of the carbamate NaOOC group [164] [reaction (a)] and the 1920 cm band is typical for absorption by sodium salts. Consequently, in 2,4-TDI interactions with high-concentration NaOH solutions, mainly reactions (a) and (b) occur that is, carbamates, amines, and sodium carbonate are predominantly formed and the contribution of the disubstituted mea [reaction (c)] is insignificant. 

---