In situ miniemulsion polymerization for waterborne polyurethanes: Kinetics and modeling of interfacial hydrolysis of isocyanate

Isocyanates hydrolysis, an important side reaction in direct synthesis of waterborne polyurethanes by miniemulsion polymerization has been studied experimentally and theoretically in the paper. A kinetic model has been developed considering the resistances due to the diffusion through the formed polymer and interfacial reaction in monomer miniemulsion. This model studied the hydrolysis process quantitatively by reaction degree as a function of time in terms of the reaction rate-controlling step. Both experimental results and reported data from literatures fit the kinetic model well. It has been found that the hydrolysis of aromatic isocyanate with high reactivity is a diffusion controlled fast reaction process, while the hydrolysis of aliphatic isocyanate with moderate reactivity is a reaction-controlled process. The hydrolysis of aliphatic isocyanate at different temperatures has also been studied and it was also found a reaction-controlled process.