It is well known that the components of microcapsule prepolymers have great influence on the structures and morphologies of the resultant self-healing microcapsules. The synthesis of high-performance self-healing microcapsules is benefited to the presence of high-content multimethylol urea in the reaction system. In this contribution, the components of microcapsule prepolymers prepared under different reaction conditions, including temperatures, pH values and mole ratio of formaldehyde to urea, were studied and quantificationally analyzed using polarized microscopic melting point meter, infrared spectroscopy and 1H NMR spectroscopy. It was found that increasing the temperature and pH value in the reaction system could significantly promote the secondary reaction respectively, resulting in the decreased yield of dimethylol urea in the reaction system. When increasing the mole ratio of formaldehyde to urea, the yield of dimethylol urea in the reaction system increased, and the yield of trimethylol urea decreased simultaneously. Furthermore, the temperature of the reaction system during the heating process was monitored, and it indicated that the temperature changed at a constant path when a fixed heating rate was performed.

Key words: microcapsule prepolymer, reaction temperature, pH value of reaction, molar ratio of formaldehyde to urea, ¹H NMR spectroscopy