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.

Vegetable oils with different chemical structures are successfully encapsulated and applied as costabilizers in miniemulsion polymerization reactions. The results are compared to hexadecane, a well-known costabilizer used for this type of polymerization. The great advantage of using vegetable oils is that besides acting as costabilizers, they are also encapsulated, increasing the application of the nanoparticles. Results show that kinetics tend to be slower with argan oil, due to the higher concentration of double bonds present in the oil. When coconut oil and jojoba oil are used, the kinetic rate kept nearly the same. The different types of costabilizers do not affect the average size of the particle, and are able to keep the miniemulsion stable throughout the reaction. DSC analysis shows a decrease in the glass transition temperature when the vegetable oils are used. However, after a long period of storage, the Tg of the polymers increases. STEM images show the formation of nanoparticles for hexadecane and the vegetable oils. However, the nanocapsule morphology appeares only when coconut oil, jojoba oil, and hexadecane are used, while for argan oil no phase separation can be detected in the polymer particle. Practical Applications: Miniemulsion polymerization reactions allow the production of polymeric nanoparticles in only one step with high encapsulation efficiency. To obtain a stable miniemulsion, it is necessary the addition of a costabilizer. The vegetable oils are chosen because besides acting as costabilizers the vegetable oils can increase the application of the nanoparticles since they have important characteristics and functionalities.

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Resumo O óleo de neem foi encapsulado em nanopartículas de poli(ácido lático-co-ácido glicólico) (PLGA) pelo método de miniemulsificação/evaporação do solvente, e estas foram caracterizadas em análises de FTIR, DSC, TGA e tamanho de partícula. Resultados mostraram que as nanopartículas formadas sao estáveis ao longo do tempo e que o óleo foi encapsulado dentro da matriz polimérica sem alteração das características químicas dos compostos.