The reaction of one equivalent of 1,2,4,5-tetrakis(pyrazolyl-methyl)benzene ligand (L) with two equivalents of Cr(THF)3Cl3 in tetrahydrofuran has produced a binuclear neutral complex of general formula [Cr2L(THF)2Cl6] (1). It was characterized by mass spectrometry, Fourier-transformed infrared, X-ray photoelectron spectroscopy, and magnetic susceptibility. Theoretical calculations supported the formation of binuclear complex (1) with each hexacoordinate metal center. This complex was active in ethylene polymerization employing methylaluminoxane as cocatalyst, with moderate activities (5.7–20.8 kg polymer/(mol precat.) (bar) (h)). The reaction parameters such as temperature, monomer pressure, and Al/Cr ratio were studied. An increase of reaction temperature produced a decreasing of catalytic activity. However, an increase in the monomer pressure did not produce a significant increase in catalytic activity. The Al/Cr ratios used to activate this complex are smaller than those reported for the tris(pyrazolyl)borate chromium complex. This system produced high-density polyethylenes with wide molecular weight, Mw, distributions between 42,280 and 74,346 and polydispersity index from 2.3 to 6.6.

A novel synthesis method of obtaining polyethylene - hydroxyapatite (HDPE-HA) composites is proposed using in situ ethylene polymerization, employing Cp2ZrCl2/MAO as catalytic system. In this work, the influence of different polymerization conditions on the HA dispersion was evaluated. The parameters studied were: stirring velocity (600-2000 rpm) and temperature (10-75°C). It was found that, combining high stirring velocities (2000 rpm) and low temperatures (10 °C), it was possible to reach good filler dispersion with the HA nanocrystals interconnected in a network without the presence of agglomerates. Thermal degradation of HDPE-HA composites involved chemical degradation reaction of first order, accompanied by formation of the gas phase inside the melt polymer.

High-density polyethylene–hydroxyapatite (HDPE–HA) composites with different filler content (5–20 %) were synthesized by in situ ethylene polymerization. Good filler dispersion was observed without formation of agglomerates. Osteoblast cell behavior in HDPE–HA composites was evaluated in terms of adhesion, alkaline phosphatase activity and proliferation. Fluorescence and scanning electron microscopy results showed good cell adhesion and proliferation, and extensive filopodium-like protrusion connected to hydroxyapatite particles.

The purpose of this research was to study the thermal degradation kinetics of nanocomposites of poly(l-lactide) (PLLA) with carbon nanotubes (CNT) in order to provide further insight into their thermal stability. Nanocomposites were prepared by solvent casting with 1, 3, and 5% by weight of pristine CNT (P-CNT) or functionalized CNT (F-CNT), and were characterized using infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, and dynamic-mechanical-thermal analysis. The kinetic parameters of thermal decomposition were determined employing Coats-Redfern method to calculate the reaction order and E2 function model to calculate the activation energy (Ea). We found no major changes in PLLA glass transition temperatures due to CNT presence, but melt-crystallization temperature increased slightly in some composites. In general, composites consisting of 3% or 5% of F-CNT had superior thermal stability than did pure polymer or P-CNT composites. This improved thermal stability was revealed by slightly higher degradation and onset temperatures, and Ea obtained from kinetic analysis. In addition, 3% or 5% of F-CNT in PLLA composites slightly enhanced the storage modulus above the glass transition. Therefore, functionalization promoted, in some extent, better morphology and dispersion of CNT into the matrix, which was responsible for improved thermal stability and thermomechanical performance of composites at higher temperatures relative to pure polymer. POLYM. ENG. SCI., 55:710–718, 2015. © 2014 Society of Plastics Engineers

In the search of an effective chemotherapy for the treatment of cancer, in this work we describe the synthesis, characterization and biological activity of two new platinum complexes. The general formula is [Pt2(L)(X)4], where L was 1,2,4,5-tetrakis((1H-pyrazol-1-yl)methyl)benzene and X were iodine (1) and chlorine (2). The most probable structure was established through a combination of spectroscopic analysis and density functional theory (DFT) calculations. Studies of interaction of complexes with DNA were carried out, and the results by spectroscopic titrations, thermal denaturation and viscosity, showed noncovalent interactions of complexes with DNA. The comet assay showed damage to cellular DNA. Inhibition assays of thioredoxin reductase (TrxR) were carried out, and the compounds showed notable inhibitory activity on the enzyme in a concentration dependent manner, with IC50 values of 3.9 and 3.5nM for 1 and 2 respectively. Complex 2 exhibited greater inhibitory effects than complex 1 against all the tumor cell lines, with growth inhibitory effects superior to cisplatin in some cases.

El presente trabajo tiene como objetivo sintetizar matrices de polietileno de alta densidad (PEAD) de facil procesabilidad, a las cuales se les incorporaran diferentes nanocargas mediante la polimerizacion in situ de etileno empleando como sistema catalitico: Cp 2 ZrCl 2 /MAO. Para ello se estudio el efecto de la temperatura de polimerizacion (Tp: 10 a 70 °C) en las propiedades termicas y la microestructura de los diferente PEAD sintetizados. Los resultados obtenidos mostraron que un aumento en la Tp conduce a un incremento en la actividad catalitica, sin embargo, se evidencio una relacion inversa entre el aumento de la temperatura y el peso molecular (PM) de los polimeros. Los PEAD sintetizados que presentaron PM < 150.000 g/mol fueron de facil procesabilidad, siendo esta propiedad clave a la hora de procesar los polimeros. The present work aim is to synthetized high density polyethylene (HDPE) of easy processability, to incorporate different nanofilers thought out in situ ethylene polymerization using as catalytic system: Cp 2 ZrCl 2 /MAO. To achieve this objective the effect of polymerization temperature (Tp: 10 a 70 °C) on the microstructure and thermal properties was studied. Results show that an increase of Tp produced an increase on catalytic activity; however, it was observed an inverse effect on HDPE molecular weight (Mw). All HDPE synthetized with an Mw lower than 150.00 g/mol presented a good processability.

El presente trabajo tiene por objetivo sintetizar nanocompuestos mediante polimerizacion in situ de etileno usando Cp 2 ZrCl 2 /MAO como sistema catalitico con hidroxiapatita (HA) y nanotubos de carbono de pared multiple funcionalizados (NTCPMf) recubiertos con HA. Se emplearon nanoparticulas de HA tipo agujas sintetizadas por el metodo de precipitacion quimica. Los NTCPM fueron funcionalizados con una mezcla 3:1 H 2 SO 4 -HNO 3 a 80°C por 30 min. Los nanocompuestos HA-NTCPMf fueron sintetizados mediante el metodo de precipitacion quimica con y sin surfactante, incorporando en ambos casos 1% de NTCPMf. Los espectros de espectroscopia infraroja (FT-IR) del nanocompuesto HA-NTCPMf presentaron desplazamientos en las bandas de los grupos fosfatos de la HA, lo que pudiera indicar algun tipo de interaccion entre HA y los NTCPMf. This paper aims is to synthesize nanocomposites by in situ ethylene polymerization using Cp 2 ZrCl 2 /MAO as a catalyst system with hydroxyapatite (HA) and functionalized multiwalled carbon nanotubes (MWCNTf) coated with HA. Nanoparticles of HA with needle morphology were synthetized by chemical precipitation method. The MWCNT were functionalized with a 3:1 mixture H 2 SO 4 : HNO 3 at 80°C for 30 min. HA-MWCNTf nanocomposites were synthesized by the chemical precipitation method with and without surfactant (sodium dodecylsulfate, SDS) incorporating 1% of MWCNT. FT-IR spectra presented shifts of the bands in the phosphate groups of HA in the HA-NTCPMf.

The chemical, thermal, thermo‐mechanical, and morphology properties of poly( L ‐lactide) (PLLA) and poly( D , L Lactide‐ co ‐glycolide) (PLGA) composites with 30% hydroxyapatite (HA) were evaluated. The composites were prepared employing the solvent casting technique. The degradation kinetic parameters were obtained using the Coats–Redfern integral method for the reaction order and the E 2 function methodology to calculate the activation energy ( E a ). The addition of HA to these polymers matrices increased their glass transition temperature. This was confirmed by differential scanning calorimetery and dynamic–mechanical–thermal analysis. Also, the presence of HA increased the crystallization temperature of PLLA, implying a nucleation effect. The PLLA‐HA and PLGA‐HA composites exhibited better thermal stability, higher decomposition temperature, and higher activation energy for the decomposition process than the neat polymers. Morphology and dispersion of the filler are highly responsible for the thermal and mechanical properties of the composites, the PLGA‐HA composites showed a well dispersion but no improvement on storage modulus was found. On the other hand, the storage modulus ( E ′) of PLLA‐HA was enhanced, with respect to the neat polymer, mainly at temperatures above the glass transition. POLYM. COMPOS., 34:1433–1442, 2013. © 2013 Society of Plastics Engineers

Los complejos TpTiCl2(OR) (Tp = Hidrotris(pirazolil)borato; R = Et, i-Pr, n-Bu) fueron evaluados en la copolimerizacion de etileno con 1-hexeno. La activacion de estos complejos con polimetilaluminoxano (P-MAO) mostro un buen desempeno catalitico para la produccion de copolimeros; sin embargo, la inclusion del comonomero afecto negativamente la actividad catalitica respecto a la obtenida en la homopolimerizacion. Estos sistemas fueron capaces de producir polietilenos con un porcentaje de incorporacion molar de 1-hexeno maximo del 6%. ABSTRACT The TpTiCl2 (OR) (Tp = Hydrotris (pyrazolyl) borate; R = Et, i-Pr, n-Bu) complexes were evaluated according to their efficiency towards the copolymerization of ethylene with 1-hexene. A good precatalyst response to copolymerization was observed when they were activated with P-MAO. However, the catalytic activity was negatively affected with regard to homopolymerization. Polyethylenes with a maximum of 6 mol-% of a-olefin incorporation were obtained by this catalytic system.Keywords: Hydrotris (pyrazolyl) borate, Alcoxy group, Copolymerization, Ethylene, 1-Hexene.

Chemical and thermal characterization of poly(d,l-lactide-co-glycolide) (PLGA) composites filled with hydroxyapatite (HA) or carbon nanotubes (CNT) were evaluated by infrared spectroscopy, differential scanning calorimetry, thermogravimetry, and dynamic-mechanical-thermal analysis. The morphology and distribution of the nanoparticles were studied by transmission electron microscopy. The composites were prepared by solvent casting using 30% HA or 1, 3, and 5% of pristine and functionalized CNT as nanoparticles and PLGA 75: 25 and PLGA 50: 50 as copolymer matrix. The Coats-Redfern and E-2 function methodologies were used to calculate the reaction order and the activation energy (E-a) of the thermal degradation process. It was found that the addition of nanoparticles increased the glass transition temperature (T-g) of the composites. Also, higher degradation temperatures and E-a values were obtained for PLGA-HA composites and compared with the neat copolymer, and the opposite behavior was exhibited by PLGA-CNT composites. The thermal and mechanical properties were highly dependent on the morphology and dispersion of the filler. The functionalization process of CNT promoted, to some extent, a better distribution and dispersion of CNT into the matrix, and these composites exhibited a slight enhancement on storage modulus. On the other hand, PLGA-HA composites showed a good dispersion but no improvement on the storage modulus below T-g. (C) 2012 Society of Plastics Engineers

In situ ethylene polymerization was used to synthesize high density polyethylene - hydroxyapatite (HDPE-HA) composites, employing Cp2ZrCl2/MAO as catalytic system. A good dispersion of HA into the HDPE matrix was obtained when the following synthesis conditions were combined: high stirring velocities (2000 rpm), low quantities of solvent (100 mL), and 10 degrees C. Under these conditions different filler content was used to synthetized HDPE-HA composites. An interaction between HA and HDPE was obtained by FTIR. On the other hand, thermal analysis indicated that no significant differences were observed between HDPE and the composites.