Abstract This work aims to study the cationic miniemulsion polymerization of styrene catalyzed by iron-containing imidazolium-based ionic liquids. The polystyrenes had very high number-average molar mass around 1300 kg mol-1 at 85 °C, molar-mass dispersity close to 2.0 and glass transition temperature higher than 102 °C with average particle diameter that remained practically unchanged during the reaction, indicating that the monomer droplets correspond to the polymerization locus. First-order kinetics up to a limit conversion, along with the increase in molar mass as the temperature decreases, styrene polymerization at low temperatures and catalyst inability to polymerize monomers that react exclusively via free radical and/or anionic polymerization, indicate the cationic nature of polymerization. 1H-NMR and 13C-NMR spectra suggested the formation of polystyrene, allowing for tacticity distribution quantification: 10% isotactic, 20% atactic and 70% syndiotactic configurations. TEM micrographs confirmed the formation of spherical polymer nanoparticles and the presence of catalysts in the polymer matrix.
Abstract A novel nanoencapsulation of n-hexadecane in high molecular weight polystyrene nanoparticles for thermal energy storage was carried out by miniemulsion polymerization using an iron-containing imidazolium-based ionic liquid (IL) as catalyst. The particle size, morphology, molecular weight, and thermal performance of nanoparticles containing the phase change material (PCM) were measured by dynamic light scattering, transmission electron microscopy, gel permeation chromatography, and differential scanning calorimetry, respectively. The nanoparticles were regular spherical, with narrow size distribution and particle size ranged from 138 nm to 158 nm. The enthalpy of melting for the nanoencapsulated PCM increased from 19 J/g to 72 J/g, as the content of n-hexadecane used increased from 20 wt% to 50 wt%. In addition, the nanoparticles showed thermal reversibility after 100 thermal cycles. The high molecular weights of the polymer, up to 1800 kDa, that could be reached with this IL may have contributed positively to this thermal behavior.
Abstract Recently, the physical and chemical effects of ultrasound in polymeric materials synthesis have attracted great attention. This work presents the synthesis of novel polymeric materials by polymerization of isophorone diisocyanate with different polyols. Polymers were synthesized by step miniemulsion polymerizations, using ultrasound bath and thermostatic bath. The effects of ultrasound, temperature and polyol type were evaluated by Fourier transform infrared spectroscopy, gel permeation chromatography, dynamic light scattering and titrimetry. Polymerization under ultrasound bath showed that different reaction temperatures in the range between 50 °C and 80 °C directly influence the molecular weight of the polymers, urea/urethane formation and increase of diisocyanate consumption rate. In addition, different polyols used in polymerizations in miniemulsion had a significant effect on the characteristics of the resulting poly(urea-urethane) nanoparticles. Finally, ultrasound assisted polymerizations showed a faster diisocyanate consumption rate, but did not lead to enhanced molecular weights.
Abstract Cellulases are efficient enzymes for the conversion of cellulose into glucose. Their use in immobilized form enables them to be reused in successive cycles in many biotechnological processes. Unlike conventional methods of immobilization by covalent bonding, in miniemulsion polymerization the immobilization of enzyme and the synthesis of polymer nanoparticles (support) occur simultaneously. Based on these aspects, the immobilization of cellulose on poly(methyl methacrylate) (PMMA) nanoparticles by miniemulsion polymerization was studied. The surfactant type (non-ionic and ionic) and latex pH showed great influence on cellulase activity. High activity values were obtained only when non-ionic surfactant (Lutensol AT50) and buffering agent (NaHCO3) were used simultaneously. MMA polymerization rate and final monomer conversion were not affected by the presence of cellulase. The maximum immobilization efficiency (60%) was obtained when 6 wt.% of cellulase was used and stable PMMA nanoparticles (133 nm) were obtained. The relative activity profile of immobilized cellulase, for pH as well as temperature, was similar to that reported for the free form. Immobilized enzyme keeps its activity throughout seven days when stored at 4 ºC and phosphate buffer pH 6.0. Based on the results obtained in this work, miniemulsion polymerization as a method for cellulase immobilization on PMMA nanoparticles showed to be a promising technique with high possibility of industrial application.
Abstract Poly(Thioether-Ester) nanoparticles synthetized via thiol-ene polymerization from a renewable castor oil monomer are produced by miniemulsion polymerization and emulsification/evaporation of pre-formed polymer. Its antioxidant activity, probably due to the oxidation of sulfide groups, is confirmed by 2,2-diphenyl-1-picryl hydrazyl (DPPH) free radical-scavenging and β-carotene/linoleic acid assays, with an amount of polymer required to reduce the initial concentration of DPPH· radicals by 50% of ~195 µg.ml-1 promoting hydrogen or electron exchange and the capability to prevent lipid peroxidation of ~55%. The results show a promising application in food packing.
ABSTRACT Enzymatically crossliked gelatin hydrogel was submitted to two different drying methods: air drying and freeze drying. The resulting polymeric tridimensional arrangement (compact or porous, respectively) led to different thermal and swelling properties. Significant differences (p < 0.05) on thermal and mechanical characteristics as well as swelling in non-enzymatic gastric and intestinal simulated fluids (37 ºC) were detected. Water absorption data in such media was modelled according to Higuchi, Korsmeyer-Peppas, and Peppas-Sahlin equations. Freeze dried hydrogel showed Fickian diffusion behavior while air dried hydrogels presented poor adjustment to Higuchi model suggesting the importance of the relaxation mechanism at the beginning of swelling process. It was possible to conclude that the same gelatin hydrogel may be suitable to different applications depending on the drying process used.
ABSTRACT: The encapsulation of progesterone in poly (hydroxybutirate-co-hydroxyvalerate) (PHBV), poly (ε-caprolactone) (PCL), poly (L-lactic acid) (PLLA) nanoparticles and PHBV/PCL and PHBV/PLLA blend nanoparticles was investigated in this research. Nanoparticles were produced by miniemulsion/solvent evaporation technique with lecithin as surfactant and were characterized regarding to z-average diameter (Dz) and polydispersity (PDI), progesterone recovery yield and encapsulation efficiency. Possible interactions between progesterone and the polymer matrices were investigated by Fourier Transform Infrared Spectroscopy (FTIR). High recoveries (up to 102.43±1.80% for the PHBV/PLLA blend) and encapsulation efficiencies (up to 99.53±0.04% for PCL) were achieved and the nanoparticles presented narrow size distribution (0.12±0.03 for PLLA). PCL nanoparticles (217.5±2.12nm) presented significant difference with the Dz from all the other formulations (P<0.05). The most evident interaction between progesterone and the nanoparticles polymeric matrix was found to PHBV/PCL due to the increase in the intensity of the band located in 1631 cm-1.
RESUMO: A encapsulação de progesterona em nanopartículas de poli(hidroxibutirato-co-hidroxivalerato) (PHBV), poli (ε-caprolactona) (PCL), poli (L-ácido lático) (PLLA) e em nanopartículas blenda de PHBV/PCL e PHBV/PLLA foi investigada neste trabalho. As nanopartículas foram produzidas pela técnica de miniemulsificação/evaporação do solvente com lecitina como surfactante e foram caracterizadas em relação ao diâmetro médio em intensidade (Dz) e o índice de polidispersão (PDI), rendimento de recuperação e eficiência de encapsulação de progesterona. Possíveis interações entre progesterona e as matrizes poliméricas foram investigadas por Espectroscopia de Infravermelho por Transformada de Fourier (FTIR). Valores elevados de rendimento de recuperação (de até 102,43±1,80% para a blenda PHBV/PLLA) e eficiência de encapsulação (de até 99,53±0,04% para PCL) foram obtidos e as nanopartículas apresentaram distribuição de tamanho estreita (0,12±0,03 para PLLA). As nanopartículas de PCL (217,5±2,12nm) apresentaram diferença significativa com todas as outras formulações (P<0,05) quanto ao Dz. A interação mais evidente entre progesterona e a matriz polimérica das nanopartículas foi para a blenda PHBV / PCL, devido ao aumento na intensidade da banda localizada em 1631 cm-1.
Miniemulsion homopolymerization reactions of methyl methacrylate (MMA) and styrene (STY) using poly(L-lactide) as co-stabilizer were carried out in order to prepare poly(L-lactide)/poly(methyl methacrylate) (PLLA/PMMA) and poly(L-lactide)/polystyrene (PLLA/PS) binary blend nanoparticles. The effect of PLLA concentration on methyl methacrylate (MMA) and styrene (STY) homopolymerization reactions was evaluated. It was found that the incorporation of PLLA resulted on acceleration of MMA and STY homopolymerization reactions and led to a molar mass increase of up to 70% for PS in PLLA/PS blend nanoparticles in relation to those prepared without PLLA, which can be attributed to an increase of reaction loci viscosity (gel effect). PLLA also acted as an efficient co-stabilizer, since it was able to retard diffusional degradation of droplets when no other kind of co-stabilizer was used. Two isolated Tgs were found in both PLLA/PMMA and PLLA/PS blend nanoparticles which can be associated to blend immiscibility. TEM images corroborate these results, suggesting that immiscible PLLA/PMMA and PLLA/PS blend nanoparticles could be formed with two segregated phases and core-shell morphology.
Polyurethane nanoparticles (NPs) are promising candidates for the controlled and targeted delivery of therapeutics in a variety of biomedical applications. In this work, a report is made of NPs produced by miniemulsion polymerization with isophorone diisocyanate (IPDI) and castor oil, glycerol, and poly(ethylene glycol) (PEG) with molar masses 400 and 1000 as monomers and Tween 80, Span 80 and Lutensol AT 25 as surfactant and açaí oil as costabilizer. Stable dispersions with sizes between 100 - 500 nm were achieved. The effects from polyol, types and concentration of surfactant and reaction temperature on the size of the NPs and weight average molar mass were evaluated. Morphological characterization was accomplished using images from Transmission Electron Microscopy (TEM) and Scanning Electron Microscope (SEM).