Effect of the polymer shell in imidazole microencapsulation by solvent evaporation method

In this paper, the microencapsulation of imidazole derivatives (1-methylimidazole and 2-phenylimidazole, 1-MIm and 2-PhIm, respectively) as core materials into polymeric shells has been studied. Imidazoles are used as latent curing agents for epoxy resins with application for example in the manufacturing of electronic devices. Microencapsulation of imidazoles has been carried out by solvent evaporation and different experimental parameters (e.g. type of polymer for the shell) have been analyzed and the final properties of the capsules obtained (particle size, morphology or thermal properties). Characterization has been carried out using differential scanning calorimetry (DSC) and thermal gravimetry analysis (TGA) for the thermal properties and determination of the imidazole content (%) into the capsules, and scanning electron microscopy (SEM) for the morphological characterization. Using infrared spectroscopy (IR), chemical characterization of the capsules has been carried out, confirming the presence of both components imidazole and polymer in the case of the microcapsules prepared with 2-PhIm. The reaction mechanism of the curing process of a standard epoxy resin with the different microencapsulated imidazoles has been also studied. Results have shown that the thermal stability of the capsules and the weight losing rate of the imidazole in the capsules depend on the polymer used for the shell.