Polymer microcapsules by interfacial polyaddition between styrene–maleic anhydride copolymers and amines

In the present study, styrene–maleic anhydride (SMA) copolymers were used as wall-forming materials in microencapsulation. The capsule membranes were formed by polyaddition at the interface between SMA copolymers dissolved in a dispersed relatively hydrophilic oil phase such as ethyl acetate, and a polyamine dissolved in the continuous aqueous phase. Microcapsules containing more hydrophobic core oils were prepared by either increasing the ratio of styrene to maleic anhydride groups in the copolymer, or by incorporating t-butyl styrene instead of styrene into the copolymer. Model compounds for insect sex pheromones, such as dodecyl acetate and dodecanol, were encapsulated in such SMA microcapsules, and release from these microcapsules into air was monitored over several weeks at room temperature. The relatively fast rate of release of core materials was attributed to the porous structure of the capsule walls, as confirmed by transmission and environmental scanning electron microscopy.