Amilton M. Santos

Emulsion copolymerization of styrene and n‐butyl acrylate in presence of acrylic and methacrylic acids: Effect of pH on kinetics and carboxyl group distribution

The batch emulsion copolymerization of styrene with n-butyl acrylate in the presence of acrylic and methacrylic acids was investigated. Values of reaction rate and conversion observed at different pH values were examined. The effect of pH on the glass transition temperature of the polymers was also investigated and the results compared with model predictions. Its effect on the distribution of the carboxyl groups at different positions within the emulsion system (surface and core of particles, and in the aqueous phase) was also analyzed. Three methods were used to measure the number of carboxyl groups: conductimetry, organic phase potentiometry, and titration with a solution of sodium hydroxide in methanol.

High Solids Content, Soap-Free, Film-Forming Latexes Stabilized by Laponite Clay Platelets

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.

A combined hardware/software sensing approach for on-line control of emulsion polymerisation processes

In the present work, a new strategy for the on-line determination of information concerning a free radical polymerisation (overall and individual monomer conversions, and the product of the number of radicals per particle multiplied by the number of particles) is presented. It is based on the construction of a non-linear observer that uses information obtained via a new adaptive inferential calorimetric measurement scheme. The results, presented for the case of the emulsion copolymerisation of methyl methacrylate (MMA) and vinyl acetate (VAc), show that with only a rough model of the physical process, it is possible to obtain reliable estimates of the evolution of the polymerisation reaction.

Study of the thermal decomposition of potassium persulfate by potentiometry and capillary electrophoresis

Two methods of analysis, potentiometry and capillary electrophoresis, were used to study the decomposition of potassium persulfate (KPS) in aqueous solutions. The experiments were carried out in a glass reactor equipped with continuous control of temperature and pH during the reaction. The effect of the pH on the decomposition of KPS was investigated. The rate of KPS decomposition in the presence of a variety of additives (surfactants, inhibitor, monomer-like molecules, and monomers), which are used in emulsion polymerization recipes, was also studied over the temperature range of interest. The rate of disappearance of the persulfate ion was greatly increased in the presence of hydroquinone, but changed very little in the presence of surfactants.

Synthesis of multi-hollow clay-armored latexes by surfactant-free emulsion polymerization of styrene mediated by poly(ethylene oxide)-based macroRAFT/Laponite complexes

We report the surfactant-free emulsion polymerization of styrene mediated by a trithiocarbonate poly(ethylene oxide)-based macromolecular RAFT agent (PEO2K-TTC, Mn(PEO) = 2000 g mol−1) in the presence of Laponite clay platelets. Adsorption studies revealed high affinity of the macroRAFT for Laponite. The resulting macroRAFT/clay complexes were used to control the growth of polystyrene chains and generate clay-armored latexes. Undesirable effects observed under the same conditions in the absence of clay, such as rate retardation, a long induction period and loss of colloidal stability, were not observed when the macroRAFT was immobilized on the clay surface. A minimum amount of macroRAFT was necessary to ensure a good control of the polymerization and a narrow molar mass distribution while a too large amount led to similar effects as in the absence of clay due to partitioning of the free non-adsorbing PEO2K-TTC macroRAFT. By a careful selection of the macroRAFT and monomer concentrations, stable multi-hollow clay-armored composite latex particles containing embedded PEO and composed of polymer chains of controlled and narrowly distributed molar masses could be successfully obtained by this technique.

On‐line monitoring of methyl methacrylate–vinyl acetate emulsion copolymerization

An adaptive calorimetric method, coupled with state estimators for emulsion copolymerization, is shown to provide accurate, on-line information on the evolution of the composition and kinetics of an emulsion copolymerization. This method was evaluated for the emulsion copolymerization of methyl methacrylate–vinyl acetate (MMA–VAc) under nonisothermal conditions. In addition to providing on-line estimates of the number of moles of each polymerizing species in the reactor, the state estimator provides a value for a lumped kinetic parameter proportional to the product of nNp. This information can be combined with off-line measurements to study the evolution of polymerization kinetics and to explain the trends observed for the molecular weight distribution and glass transition temperatures. Values of n were found to vary from 0.5 to 30 for the homopolymerization of MMA. However, the presence of VAc in the copolymerizing system drastically reduces n. This can lead to a dramatic increase in the average molecular weight of the copolymer since it alters the ratio of propagation to termination in the polymerizing particles.

Tri-Block Copolymers Obtained by RAFT Polymerization: A Promising Material for Drug-Delivery Systems

Tri-block copolymer with pH- and thermo-responsive consisting of poly(t-butylacrylate) and poly(vinylcaprolactam), (PtBA/PVCL) were prepared by RAFT polymerization and characterized by gel permeation chromatography (GPC) and 1H NMR. PtBA and PVCL were used as macro chain-transfer agents (MCTA) to synthesize PtBA-b-PVCL-b-PtBA and/or PVCL-b-PtBA-b-PVCL, which after partial hydrolysis led to amphiphilic tri-block copolymers P(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA) and/or PVCL-b-P(tBA-co-AA)-b-PVCL.

Thermally-sensitive and Biocompatible Poly(N-vinylcaprolactam): A Kinetic Study of Free Radical Polymerization in Ethanol

Using nuclear magnetic resonance (1H-NMR), a kinetic study on the polymerization of N-vinylcaprolactam (NVCL) was performed under different polymerization conditions. The homopolymers were synthesized by free radical polymerization in ethanol, and azobisisobutyronitrile (AIBN) and 3-mercaptopropionic acid were used as the initiator and chain transfer agent (CTA), respectively. Moreover, the effect of the monomer concentration, initiator concentration and polymerization temperature on the kinetics of the reaction was evaluated. The results revealed that the aforementioned parameters had a significant effect on the polymerization rate (Rp ): as the monomer and initiator concentration increased, an increase in Rp and the overall activation energy was observed. Poly(N-vinylcaprolactam) (PNVCL) is a thermoresponsive and biocompatible polymer that possesses a LCST (low critical solution temperature) near physiological temperature. Thermoresponsive polymers with low molar masses are useful for biomedical applications; thus, the effect of the molar mass on the polymerization rate and the LCST of PNVCL was studied. The number-average molar mass () and the polydispersity of the homopolymers were measured with a gel permeation chromatograph coupled to a triple detector (GPC/SEC/LALS), and the LCST of the PNVCL was determined by UV-visible analyses.

Estudo Cinético da Redução da Massa Molar do Poli (3-Hidroxibutirato-co-3-Hidroxivalerato) (PHBHV)

Neste trabalho foi realizado um estudo cinetico da reducao da massa molar do poli(3-hidroxibutirato-co-3-hidroxivalerato) (PHBHV) em tres diferentes metodologias: hidrolise acida com acido cloridrico, transesterificacao com hexilenoglicol ou etilenoglicol e reducao na presenca do borohidreto de sodio (NaBH4). Foram investigados os parâmetros de processo: tempo, temperatura, tipo e concentracao de catalisadores. Os resultados de reducao de massa molar foram analisados pelo modelo cinetico de ordem n. A reducao com NaBH4 foi mais eficiente do ponto de vista cinetico, tendo em vista os parâmetros: constante de reacao k e energia de ativacao (Ea), uma vez que os valores observados foram significativamente maiores em comparacao com os calculados para os demais metodos.

Synthesis and characterization of thermo-responsive particles of poly(hydroxybutirate-co-hydroxyvalerate)-b-poly(N-isopropylacrylamide)

A new kind of thermo-responsive particles were prepared by the self-assembly technique, comprising poly(hydroxyvalerate-co-hydroxybutirate)-b-poly(N-isopropylacrylamide)/ (PHBHV-b-PNIPAAm) block copolymers. The hydrophilic part PNIPAAm was synthesized by Reversible Addition- Fragmentation chain Transfer (RAFT) polymerization. Particles with core-shell morphology were obtained with hydrophilic outer shells and hydrophobic inner cores. Dexametasone acetate (DexAc) was used as a model drug with an encapsulation efficiency of 77%. The release of DexAc in aqueous solution was strongly dependent on temperature, suggesting that PHBHV-b-PNIPAAm particles can be used as a thermo-responsive carrier material with external control in a drug release system.