Efficient microencapsulation of a liquid isocyanate with in situ shell functionalization†
We report on a one-pot, facile approach for the encapsulation of the liquid hexamethylene diisocyanate isocyanurate trimer in polyurea microcapsules formed via the oil-in-water interfacial reaction of an uretonimine-modified diphenyl methane diisocyanate trimer with triaminopyrimidine, with in situ shell functionalization/modification using different types of hydrophobic agents. Remarkably, the use of hexamethylenedisilazane resulted in microcapsules of about 70 μm in diameter, with a smooth outer surface and a high isocyanate core content up to 85 wt% as determined by quantitative online FT-IR analysis of the extracted core. On the other hand, the use of an alkylamine, fluorinated aromatic amine and/or perfluoride amine provided microcapsules of approximately 100 to 150 μm in diameter containing around 65–75 wt% of the isocyanate core content, with the outer shell surface bearing pendant hydrophobic groups as confirmed by SEM-EDX. The effects of the functionalizing compound on the microcapsule properties such as shell morphology, size distribution and stability were assessed. After one day immersion in water, the initial isocyanate content of the microcapsules with a non-functionalized shell dropped rapidly from 49 to 15 wt%, whereas the ones with the modified shell structure maintained their core content, suggesting a significantly enhanced microcapsule stability.