N,N-diethyl-meta-toluamide (DEET), an insect repellent, can be successfully encapsulated in poly(n-butyl methacrylate-comethyl methacrylate) nanospheres via direct miniemulsion polymerization. Stable and low polydisperse nanospheres with a number average diameter of 114 AE 37 nm were obtained. It is shown that DEET is an effective costabilizer and that sodium lauryl sulfate is a suitable surfactant. The nanospheres glass-transition temperature (T g ) can be tuned by adjusting the ratio between n-butyl methacrylate and methyl methacrylate in the monomer formulation. The repellent reduced the polymerization reaction rate and the copolymer molecular weight, and changed the nanoparticle morphology. The release rate of the encapsulated DEET provides repellency for over 9 h and is and more controlled when compared to the free DEET. Results show the mechanism of release is temperature dependent. At temperatures close to and lower than the polymer T g , polymer relaxation is the limiting mechanism. At higher temperatures, Fickian diffusion limits the overall release. Thus, the DEET release rate can be tuned by adjusting the copolymer T g . This ensures this material a great potential as temperature-dependent delivery system. An alternative of protection for this vulnerable population is the encapsulation and further application of DEET in fabrics, for instance. Thus, not only the DEET would not be applied directly to the skin, but its evaporation could be slowed down, increasing the repellency time of this substance.The encapsulation of substances can be achieved with a large number of techniques, like coacervation, 8 solvent evaporation, 9 and polymerization techniques 10,11 and there is also a considerable variety of carrier systems, such as liposomes, polymeric nanocapsules, micelles, etc. [12][13][14] One advantage of using polymeric systems for encapsulation is the possibility of tailoring the polymer chain, which makes them suitable for a wide range of applications, like drug delivery, 15,16 controlled release of fragrances, 17-19 and cells encapsulation. 20,21 The miniemulsion polymerization is a simple technique which allows the formation of polymer particles with controlled Additional Supporting Information may be found in the online version of this article.
