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.

. The hydrolysis of isocyanate is an important side reaction during the direct synthesis of waterborne polyurethanes (PUs) by miniemulsion polymerization. The hydrolysis mechanisms and the interplay of the physical diffusion and the chemical rate process were investigated. A kinetic model has been developed considering the resistances due to the diffusion through the formed polymer and interfacial reaction in monomer miniemulsion. 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.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of waterborne polyurethanes by in situ miniemulsion polymerization.
► Interfacial hydrolysis of isocyanate in synthesis of waterborne polyurethanes.
► Kinetic model of the interfacial reaction describes the hydrolysis process.
► Hydrolysis of IPDI over a range of temperature is controlled by reaction.