Kinetic models of polyurethane synthesis

Modern technological practice, particularly the various types of chemical processing, use a great variety of formulations for the synthesis of polyurethanes. Therefore it is nearly impossible to create a general kinetic model which would be valid for various polymerizing systems. However, the same general approach to creating such models can be used for different cases. Therefore, it is useful to demonstrate the method used to construct a model and its characteristic kinetic equations for some typical cases. 

The most comprehensive kinetic model for the synthesis of polyurethanes was developed by Macosko and his team.44 46 In all cases the heart of the model is the degree of conversion, p, which is defined for polyurethane synthesis as 

The authors of the original publications mention that the kinetic equation is rather complicated but does not degenerate into an nth-order kinetic equation. However, in order to use the experimental data for practical calculations and computer simulations of a process, they can be described by the following equation  

For the specific polymerizing system, mentioned above, ko = 3.14 x 108 (time in min) U=64 kJ/mol and the enthalpy of reaction equals 60.33 kJ/equiv. 

Equations of an analogous type can be used for other polyurethane-forming systems, although the numerical values of the constants may be different, because Eq. (2.29) must be treated primarily as empirical. It is reasonable to expect that an adequate approximation for other systems would be n equal to 2 (which is typical for polyaddition reactions) and m also equals to 2. Such values of the constants m and n are valid, for example, for RIM-2200 (produced by Union Carbide ), which consists basically of polyester and 4.4-diphenylmethane diisocyanate.4 

---