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°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 µm in diameter. The phase transition temperatures of DOA, MU‐DOA, and MU‐DOA microspheres were 30.3°C, 21.1°C, and 20.1°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.

Keywords:

• N‐methylolurea
• dodecylamine
• self‐condensation
• microcapsule
• microspheres

Acknowledgment

This work was supported by Kangwha County's special research fund.