Preparation of highly uniform and crosslinked polyurea microspheres through precipitation copolymerization and their property and structure characterization

Abstract

Crosslinked polyurea (PU) microspheres were prepared by precipitation polymerization of isophorone diisocyanate (IPDI) and diethylenetriamine (DETA) in the binary solvent of water–acetone. The influence of polymerization temperature, solvent composition, shaking rate and DETA amount on the microspheres was studied. Highly uniform microspheres were obtained when the polymerization was conducted at 30 °C to 50 °C. A slight decrease in the size of microspheres along with a slightly broadened size distribution was detected with increase in polymerization temperature. With increased water amount in the solvent, the polymerization rate was promoted, the size of the microspheres regularly reduced and the yield regularly enhanced slightly. Microspheres with the best uniformity were observed with water content from 30 wt% to 40 wt%. The results demonstrate that, although PU crosslinking was changed with H₂O–acetone ratio in the solvent and polymerization temperature, DETA–IPDI ratio was the most effective means for control of PU crosslinking. The crosslinking was also confirmed by tests on microsphere swellability and light transmittance of the spheres' dispersion in acetic acid. TGA analysis demonstrates that the crosslinked PU was thermally stable. An attempt, based on infrared analysis, to describe the PU structure and its variation with monomer ratio was established. The results were in good agreement with those obtained by theoretical estimation. This work provides a reliable pathway to the preparation of uniform PU microspheres with easily controllable crosslinking.