Polymer International Polym Int 57:995–1006 (2008) Interfacial polymerization of an epoxy resin and carboxylic acids for the synthesis of microcapsules Oana Pascu, Ricard Garcia-Valls and Marta Giamberini ∗ University Rovira i Virgili, Department of Chemical Engineering, Av. Pa¨ ısos Catalans, 26-43007 Tarragona, Spain Abstract BACKGROUND: Microencapsulation technology promises new applications such as intelligent microstructures, phase change materials and self-healing composites. Microcapsule synthesis and characterization have been researched extensively; however, the well-known polymerization between epoxy resins and carboxylic acids has not been used to prepare microcapsules. RESULTS: Microcapsules were prepared by interfacial polymerization of an oil-in-water emulsion which contained a commercial epoxy resin and multifunctional carboxylic acids. The microcapsules obtained were characterized using optical microscopy and scanning electron microscopy. Experiments performed at lower stirring rates led to larger microcapsules, in the range 100–400 μm, while higher stirring rates resulted in microcapsules in the range 10–50 μm. CONCLUSIONS: Microcapsules can be prepared by interfacial polymerization of epoxy resins, an extensively studied and widely used class of polymers. By means of NMR characterization we gained insight into the mechanism of polymerization at the interface wherein products coming from the more hindered ring opening as well as from intermolecular transesterification are identified. The presence of a crosslinker affects the morphology of the external microcapsule surface.  2008 Society of Chemical Industry Keywords: epoxy resins; microencapsulation; polyesters INTRODUCTION Microcapsules are small particles which contain an active agent or core material surrounded by a coating or shell. There is no universally accepted size range for the particles to be classified as microcapsules; however, commercial microcapsules typically have a diameter of between 3 and 800 μm and contain 10–90% core. 1 Microcapsules can encapsulate various substances, such as gases, liquid and solids; coating substances can also be selected from a wide variety of natural or synthetic polymers, depending on the substance to be coated and on the desired characteristics of the final microcapsules. By properly selecting the core material and the membrane which constitutes the shell, it is possible to prepare microcapsules with a variety of functions. A large variety of materials have been encapsulated, including adhesives and coatings, 2,3 food additives, 4 catalysts, 5 dyes, 6 pharmaceuticals 7 and inks. 8 Nowadays microencapsulation technology is promising for new applications in the fields of intelligent microstructures and microsystems, 9 as well as in the fields of phase change materials 10 and self-healing composites. 11 In order to develop new and versatile applications of microcapsules, their synthesis and characterization have been researched extensively. Among the several methods used in order to prepare microcapsules, in the literature much interest has been devoted to interfacial polymerization. A unique feature of this technology is that the capsule shell is formed at or on the surface of a droplet or particle by polymerization of reactive monomers. 1 According to this synthetic approach, a droplet suspension containing one multifunctional monomer is formed in an immiscible solvent containing a complementary monomer in the presence of a suitable stabilizer. As soon as the polymer is formed, it precipitates on one side of the interface, thus forming the primary membrane, and the reaction slows down since the diffusion of the monomers gets restricted by the polymeric wall. The thickness of the wall increases and the growth can occur either on one side of the interface or on the other side depending on the nature of the membrane and its affinity for the monomers. During this growth, the layer morphology changes and becomes porous; pores are formed as a consequence of the precipitation of polymer at the interface of solvent droplets ∗ Correspondence to: Marta Giamberini, University Rovira i Virgili, Department of Chemical Engineering, Av. Pa¨ ısos Catalans, 26-43007 Tarragona, Spain E-mail: marta.giamberini@urv.net (Received 20 February 2008; revised version received 29 February 2008; accepted 8 May 2008) Published online 9 June 2008; DOI: 10.1002/pi.2438  2008 Society of Chemical Industry. Polym Int 0959–8103/2008/$30.00