The reversible addition−fragmentation chain transfer (RAFT) polymerization technique was used to synthesize random copolymers of poly(ethylene glycol) methyl ether acrylate) (PEGA) and n-butyl acrylate (BA) and terpolymers of acrylic acid (AA), PEGA and BA with a trithiocarbonate reactive end-group. These macromolecular RAFT agents (macro-RAFTs) were subsequently adsorbed at the surface of size-monodisperse colloidal silica particles with diameters varying between 40 and 450 nm. Adsorption isotherms for both macro-RAFTs could be well fitted to the Langmuir adsorption model, the AA-based macro-RAFT agent showing however a lower maximum adsorption. The adsorbed macro-RAFT agents were subsequently chain extended with a mixture of methyl methacrylate (MMA) and BA by starved feed emulsion polymerization. Cryo-TEM analysis of the resulting hybrid latexes synthesized in the presence of the P(AA-co-PEGAco-BA) terpolymers resulted in multipod-like particles while the P(PEGA-co-BA) copolymers showed the formation of individually and multiencapsulated silica particles depending on the silica particle size. Decreasing the total silica surface area available by decreasing the silica concentration or by increasing the silica particle size resulted in limited coagulation of the latex particles due to a less efficient use of the free nonadsorbing macro-RAFT agent. The feeding process also had a strong impact on particle morphology, and snowman-like particles could be successfully achieved under batch conditions. The use of commercial silica particles instead of homemade silica led to armored latexes illustrating the determinant role of the surface properties of the macro-RAFT-coated inorganic particles in controlling hybrid particle morphology. At last, core−shell particles with a rigid silica core and a soft copolymer shell were obtained for the first time by polymerizing a film-forming monomer mixture showing the high potential of the P(PEGA-co-BA) macro-RAFT agent for the elaboration of polymer-encapsulated silica particles for coating applications.

High solids content film-forming poly[styrene-co-(n-butyl acrylate)] [poly(Sty-co-BuA)] latexes armored with Laponite clay platelets have been synthesized by soap-free emulsion copolymerization of styrene and n-butyl acrylate. The polymerizations were performed in batch in the presence of Laponite and a methyl ether acrylate-terminated poly(ethylene glycol) macromonomer in order to promote polymer/clay association. The overall polymerization kinetics showed a pronounced effect of clay on nucleation and stabilization of the latex particles. Cryo-transmission electron microscopy observation confirmed the armored morphology and indicated that the majority of Laponite platelets were located at the particle surface. The resulting nanostructured films displayed enhanced mechanical properties.

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Recebido em 14/9/99; aceito em 3/1/00 SYNTHESIS OF BUTYL BUTYRATE BY MICROBIAL LIPASE IMMOBILIZED ONTO STY-RENE-DIVINYLBENZENE COPOLYMER. This work investigates the reaction parameters of an immobilized lipase in the esterification reaction of n-butanol and butyric acid. Microbial lipase fromCandida rugosa was immobilized onto styrene-divinylbenzene copolymer (STY-DVB) and subsequently introduced in an organic medium containing substrates in appropriate concentrations. Heptane was selected as solvent on the basis of its compatibility with the resin and the enzyme. The influence of molar ratio of acid to alcohol, amount of immobilized lipase and temperature on the butyl butyrate formation was determined. The results were compared with those achieved with free lipase and Lipozyme (commercially immobilized lipase) under the same operational conditions. Keywords: lipase; organic solvent; immobilization; styrene-divinylbenzene copolymer; butyl butyrate. ARTIGO INTRODUÇÃOEmbora nos últimos anos, a utilização de enzimas na indús-tria esteja aumentando rapidamente, ainda existe um grande campo para a sua expansão. Novas enzimas vão criando oportunidades e, em alguns ramos da indústria a utilização das enzimas está apenas começando. Um exemplo típico é uso de enzimas em síntese orgânica [1][2][3][4] . Como é de conhecimento, até pouco tempo, havia a concepção de que as enzimas tinham pouca utilidade em síntese orgâ-nica, devido principalmente à idéia preconcebida de que somente o meio aquoso era propício para manter a conformação estrutural de uma enzima cataliticamente ativa. Entretanto, sabe-se atualmente que, muitas enzimas (ou complexos enzimáticos) são cataliticamente ativas em ambientes hidrofóbicos naturais com eficiência similar àquela encontrada em soluções aquosas, ou em certos casos, até superior 2,5 . Acredita-se, que as enzimas sejam cataliticamente ativas em meio orgânico porque elas permanecem na sua conformação original. A incapacidade da proteína de se desdobrar em meio não aquoso devese em parte ao fato das interações eletrostáticas entre os grupos integrantes da enzima serem aumentadas em solventes orgânicos, devido à baixa constante dielétrica da maioria dos solventes e também ao aumento do número de ligações de hidrogênio intramoleculares 6 . Isto é importante, pois o equilíbrio termodinâmico de muitos processos, como por exemplo, a sín-tese de ésteres, só ocorre em ausência de água. Em síntese orgânica, existem inúmeras vantagens no uso de enzimas que apresentam especificidade significativas para a formação de produto de tal forma que, custo de separação, purificação e tratamento de resíduos sejam minimizados 4-7 . Um grande número de trabalhos nesta área pode ser encontrado na literatura especializada, tendo em vista o interesse científico demonstrado por diversos grupos de pesquisa, no sentido de elucidar as propriedades e o comportamento de enzimas em meios não aquosos. Conseqüentemente, o número de rotas de síntese que incorporam um passo enzimático torna-se cada vez maior. Bem ilustrativos são ...

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Biodegradable and biocompatible copolymers have been often studied for the development of biomaterials for drug delivery systems. In this context, this work reports the synthesis and characterization of a novel pullulan-g-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (Pull-g-PHBHV) graft copolymer using click chemistry. Well-defined and functional pullulan backbones containing azide groups (PullN3) previously prepared by our group were successfully used for this purpose and propargyl-terminated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was prepared via transesterification using propargyl alcohol as a chain transfer agent. By an alkyne-azide cycloaddition reaction catalyzed by copper (Cu (I)) (CuAAC), the graft copolymer Pull-g-PHBHV was obtained. The chemical structures of the polymers were accessed by 1H NMR and 13C NMR FTIR. Disappearance of the bands referring to the main bonds evidenced success in the grafting reaction. Besides that, DRX, DSC and TGA were used in order to access the changes in crystallinity and thermal behavior of the material. The remaining crystallinity of the Pull-g-PHBHV structure evidences the presence of PHBHV. Pull-g-PHBHV presented lower degradation maximum temperature values than the starting materials, indicating its minor thermal stability. Finally, the synthesized material is an innovative biopolymer, which has never been reported in the previous literature. It is a bio-derived and biodegradable polymer, chemically modified, resulting in interesting properties which can be useful for their further applications as biomedical systems for controlled delivery, for example.