Catalysis of isocyanate reaction with water by DMF and its use for fast preparation of uniform polyurea microspheres through precipitation polymerization

Highly uniform polymer microspheres are widely used for a variety of applications. Uniform polyurea (PU) microspheres have been prepared by precipitation polymerization of isophorone diisocyanate (IPDI) in a binary mixture of H2O-acetone (AT). With AT replaced by N,N'-dimethylformamide (DMF) in the binary mixture, a significant acceleration effect is observed. Through measurements of the solubility of IPDI and its polymer in the binary solvents of different composition, catalytic effect of DMF is confirmed, and a mechanism of catalysis is proposed. The polymerization is carried out at different temperature with varied IPDI concentration in H2O/DMF or H2O/AT/DMF of different composition, with objective to optimize the preparation of PU microspheres. The results demonstrate that, with the polymerization done at 60 degrees C in a ternary mixture of H2O-DMF-AT, highly uniform PU microspheres are well formed with IPDI concentration of up to 13.0 wt%, which represents an increase of 3 wt% compared to the highest IPDI concentration allowed to have these microspheres in the binary solvent of H2O-AT. This is also accomplished in an obviously shortened time. PU structure and properties are briefly discussed. This work provides a simple and fast protocol for large-scale production of uniform and functional PU microspheres with DMF as a cosolvent and catalyst.