Preparation of microspheres by an emulsification-condensation method

Abstract

Microspheres were prepared using N-methylolurea-dodecylamine conjugate (MU-DOA), an emulsifiable and self-condensaible oil. MU was prepared by reacting urea and formaldehyde at 70 degrees C in alkali conditions and then conjugating it to DOA by a condensation reaction. The MU-DOA conjugate was emulsified in distilled water without an emulsifier, and then the oil droplets were hardened to obtain microspheres by a self-condensation reaction among methylols of the conjugate. The reactions of each step, e.g., the preparation of MU, the conjugation of MU and DOA, and the self-condensation of emulsified oil, were confirmed by Fourier transform infrared (FTIR) spectra. On scanning electron microscopy (SEM), the microspheres formed by the self-condensation of the emulsified MU-DOA were shown as spherical and less than 30 mu m in diameter. The phase transition temperatures of DOA, MU-DOA, and MU-DOA microspheres were 30.3 degrees C, 21.1 degrees C, and 20.1 degrees C, respectively. The lower transition temperature of MU-DOA is probably due to the bulky MU, which could reduce the intermolecular interaction of MU-DOA. Zeta potentials of the microspheres decreased from positive to negative value as pH increased from 3.5 to 10.5. The deprotonation of the amines of MU-DOA would be responsible for that result.