Ab Initio Analysis of Monomers and Dimers of Trialkylphosphine Oxides: Structural and Thermodynamic Stability

Structural and thermodynamic stabilities of monomers and dimers of trialkylphosphine oxides (TRPO) were Studied using quantum chemistry calculations. Density functional theory calculations were carried Out and the structures Of four TRPO have been determined: TMPO (methyl; R = CH(3)), TEPO (ethyl; R = CH(3)CH(2)), TBPO (n-butyl; R = CH(3)(CH(2))(3)), and TOPO (n-octyl; R = CH(3)(CH(2))(7)). TRPO homodimers were investigated considering two isomeric possibilities for each dimer. Relative binding energies and the enthalpic and entropic contributions to the Gibbs free energy were Calculated for all dimers. The formation of dimers from the individual monomeric TRPO species as a function of temperature was also analyzed. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 250-258, 2009

Phenol-furfural resins to elaborate composites, reinforced with sisal fibers - Molecular analysis of resin and properties of composites

Resol type resins were prepared in alkaline conditions (potassium hydroxide or potassium carbonate) using furfural obtained by acid hydrolysis of abundant renewable resources from agricultural and forestry waste residues. The structures of the resins were fully determined by H-1, C-13, and 2D NMR spectrometries with the help of four models compounds synthesized specially for this study. MALDI-Tof mass spectrometry experiments indicated that a majority of linear oligomers and a minority of cyclic ones constituted them. Composites were prepared with furfural-phenol resins and sisal fibers. These fibers were chosen mainly because they came from natural lignocellulosic material and they presented excellent mechanical microscopy images indicated that the composites displayed excellent adhesion between resin and fibers. Impact strength measurement showed that mild conditions were more suitable to prepare thermosets. Nevertheless, mild conditions induced a high-diffusion coefficient for water absorption by composites. Composites with good properties could be prepared using high proportion of materials obtained from biomass without formaldehyde. (c) 2008 Wiley Periodicals, Inc.

Formation and decomposition of N-alkyinaphthalimides: experimental evidences and ab initio description of the reaction pathways

The kinetics of hydrolysis of 1,8-N-butyl-naphthalimide (1,8-NBN) to 1,8-N-butyl-naphthalamide (1,8-NBAmide) and of 2,3-N-butyl-naphthalimide (2,3-NBN) to 2,3-N-butyl-naphthalamide (2,3-NBAmide), as well as the formation of the respective anhydrides from the amides were investigated in a wide acidity range. 1,8-NBN equilibrates with 1,8-NBAmide in mild alkali. Under the same conditions 2,3-NBN quantitatively yields 2,3-NBAmide. Over a wide range of acidities the reactions of the 1,8- and 2,3-N-butyl-naphthalamides (or imides) yield similar products but with widely different rates and at distinct pH`s. Anhydride formation in acid was demonstrated for 1,8-NBAmide. The reactions mechanisms were rationalized in the manifold pathways of ab initio calculations. The differences in rates and pH ranges in the reactions of the 1,8- and 2,3-N-butyl-naphthalamides were attributed to differences in the stability of the tetrahedral intermediates in alkali as well as the relative stabilities of the five and six-membered ring intermediates. The rate of carboxylic acid assisted 1,8-N-Butyl-naphthalamide hydrolysis is one of the largest described for amide hydrolysis models. Copyright (C) 2010 John Wiley & Sons, Ltd.

Valorization of an Industrial Organosolv-Sugarcane Bagasse Lignin: Characterization and Use as a Matrix in Biobased Composites Reinforced With Sisal Fibers

In the present study, the main focus was the characterization and application of the by-product lignin isolated through an industrial organosolv acid hydrolysis process from sugarcane bagasse, aiming at the production of bioethanol. The sugarcane lignin was characterized and used to prepare phenolic-type resins. The analysis confirmed that the industrial sugarcane lignin is of HGS type, with a high proportion of the less substituted aromatic ring p-hydroxyphenyl units, which favors further reaction with formaldehyde. The lignin-formaldehyde resins were used to produce biobased composites reinforced with different proportions of randomly distributed sisal fibers. The presence of lignin moieties in both the fiber and matrix increases their mutual affinity, as confirmed by SEM images, which showed good adhesion at the biocomposite fiber/matrix interface. This in turn allowed good load transference from the matrix to the fiber, leading to biobased composites with good impact strength (near 500 J m(-1) for a 40 wt% sisal fiber-reinforced composite). The study demonstrates that sugarcane bagasse lignin obtained from a bioethanol plant can be used without excessive purification in the preparation of lignocellulosic fiber-reinforced biobased composites displaying high mechanical properties. Biotechnol. Bioeng. 2010;107: 612-621. (C) 2010 Wiley Periodicals, Inc.

Derivatives of Biomacromolecules as Stabilizers of Aqueous Alumina Suspensions

The stabilization of alumina suspensions is key to the development of high-performance materials for the ceramic industry, which has motivated extensive research into synthetic polymers used as stabilizers. In this study, mimosa tannin extract and a chitosan derivative, that is, macromolecules obtained from renewable resources, are shown to be promising to replace synthetic polymers, yielding less viscous suspensions with smaller particles and greater fluidity, that is, more homogeneous suspensions that may lead to better-quality products. The functional groups of tannin present in mimosa extract and N,N,N-trimethylchitosan (TMC) are capable of establishing interactions with the alumina surface, thus leading to repulsion between the particles mainly due to steric and electrosteric mechanisms, respectively. The stabilization of the suspension induced by either TMC or mimosa tannin was confirmed by a considerable decrease in viscosity and average particle size, in comparison with alumina suspensions without stabilizing agents. The viscosity/average particle size decreased by 49/84% and 52/87% for suspensions with TMC and mimosa tannin, respectively. In addition, the increase in the absolute zeta potential upon addition of either TMC or mimosa tannin extract, especially at high pHs, points to an increased stability of the suspension. The feasibility of using derivatives of macromolecules from renewable sources to stabilize aqueous alumina suspensions was therefore demonstrated. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 58-66, 2010

Sisal Fibers Treated with NaOH and Benzophenonetetracarboxylic Dianhydride as Reinforcement of Phenolic Matrix

In this work, composites based on a phenolic matrix and untreated- and treated sisal fibers were prepared. The treated sisal fibers used were those reacted with NaOH 2% solution and esterified using benzophenonetetracarboxylic dianhydride (BTDA). These treated fibers were modified with the objective of improving the adhesion of the fiber-matrix interface, which in turn influences the properties of the composites. BTDA was chosen as the esterifying agent to take advantage of the possibility of introducing; the polar and aromatic groups that are also present in the matrix structure into the surface of the fiber, which could then intensify the interactions occurring in the fiber-matrix interface. The fibers were then analyzed by SEM and FTIR to ascertain their chemical composition. The results showed that the fibers had been successfully modified. The composites (reinforced with 15%, w/w of 3.0 cm length sisal fiber randomly distributed) were characterized by SEM, impact strength, and water absorption capacity. In the tests conducted, the response of the composites was affected both by properties of the matrix and the fibers, besides the interfacial properties of the fiber-matrix. Overall, the results showed that the fiber treatment resulted in a composite that was less hygroscopic although with somewhat lower impact strength, when compared with the composite reinforced with untreated sisal fibers. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 269-276, 2010

Crystal structure and theoretical calculations of Julocrotine, a natural product with antileishmanial activity

Julocrotine, N-(2,6-dioxo-l-phenethyl-piperidin-3-yl)-2-methyl-butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X-ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6-311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data. (C) 2007 Wiley Periodicals, Inc.

Evaluation of the light polymerization efficiency of copolymers used in dental formulations by differential scanning calorimetry

Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals, Inc.

Characterization of Polyurethane Resins by FTIR, TGA, and XRD

Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers - USF - Sao Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 263-268, 2010

Evaluation of Postpolymerization as a Function of the Storage Time of Triethylene Glycol Dimethacrylate/2,2-Bis[4-(2-Hydroxy-3-Methacryloxy-Prop-1-Oxy)-Phenyl]-propane Bisphenyl-alpha-Glycidyl Ether Dimethacrylate Copolymers Used in Dental Resins by Differential Scanning Calorimetry and Dynamic Mechanical Analysis

The aim of this work was to evaluate the effect of the storage time on the thermal properties of triethylene glycol dimethacrylate/2,2-bis[4-(2-hydroxy-3-methacryloxy-prop-1-oxy)-phenyl]propane bisphenyl-alpha-glycidyl ether dimethacrylate (TB) copolymers used in formulations of dental resins after photopolymerization. The TB copolymers were prepared by photopolymerization with an Ultrablue IS light-emitting diode, stored in the dark for 160 days at 37 degrees C, and characterized with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy with attenuated total reflection. DSC curves indicated the presence of an exothermic peak, confirming that the reaction was not completed during the photopolymerization process. This exothermic peak became smaller as a function of the storage time and was shifted at higher temperatures. In DMA studies, a plot of the loss tangent versus the temperature initially showed the presence of two well-defined peaks. The presence of both peaks confirmed the presence of residual monomers that were not converted during the photopolymerization process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 679-684, 2009

Thioxanthone Sensitized Photodegradation of Poly(alkyl methacrylate) Films

The thioxanthone-sensitized photodegradation of poly(alkyl methacrylate) films [alkyl = methyl, ethyl, butyl, and hexyl] was studied using near UV-vis light. The photooxidation process continued even after the total consumption of the sensitizer, possibly due to the excitation of the ketyl groups formed during the first stages of the process. The rate of oxidation, as well as the formation of hydroxy, peroxy, and ketyl groups was faster for polymers with larger ester groups. The decrease of the molecular weight of the degradated polymers was also larger for the hexyl substituted polymer. The side-chain size effect was attributed to the larger amount of secondary hydrogens available for abstraction by the triplet state of thioxanthone, present in the larger ester groups. The lower glass transition temperature of the hexyl substituted polymer allows a better diffusion of oxygen to the deeper layers of the films that also contributes to the faster photodegradation rate. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1283-1288, 2010