Synthesis and properties of branched polyethylene/high-density polyethylene blends using a homogeneous binary catalyst system composed of early and late transition metal complexes

Branched polyethylene/high-density polyethylene blends (BPE/HDPE) with a wide range of molecular weights, melt flow indexes (MFI), and intrinsic viscosity were prepared using the homogeneous binary catalyst system composed by Ni(alpha-diimine)Cl-2 (1) (alpha-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and {Tp(Ms*)} TiCl3 (2) (Tp(Ms*)=hydridobis(3-mesitylpyrazol-1-yl)(5-mesityl-pyrazol-1-yl)) activated with MAO and/or TIBA in hexane at two different polymerization temperatures (30 and 55 degreesC) and by varying the nickel loading molar fraction (x(Ni)). At all Temperatures, a non-linear correlation between the x(Ni) and the productivity was observed, suggesting the occurrence of a synergistic effect between the nickel and the titanium catalyst precursors, which is more pronounced at 55 degreesC. The molecular weight of the BPE/HDPE blends considerably decreases with increasing Al/M molar ratio. The melt flow indexes (MFI) and intrinsic viscosities (eta) are strongly affected by x(Ni), but the melting temperatures are nearly constant, 132 +/- 3 degreesC. Dynamic mechanical thermal analysis (DMTA) shows the formation of different polymeric materials where the stiffness vanes according, to the x(Ni) and temperature used in the polymerization reaction. The surface morphology of the BPE/HDPE blends studied by scanning electron microscopy (SEM) revealed a low miscibility between the PE phases resulting in the formation of a sandwich structure after etching with o-xylene.

Signaling path of the action of AVP on distal K+ secretion

Background. Previous studies from our laboratory have shown that luminal perfusion with arginine vasopressin (AVP) stimulates distal tubule secretory potassium flux (J(K)) via V1 receptors (Am J Physiol 278: F809- F816, 2000). In the present work, we investigate the cell signaling mechanism of this process.Methods. In vivo stationary microperfusion was performed in rat cortical distal tubules and luminal K was measured using double K+ resin/reference microelectrodes.Results. In control conditions, J(K) was 0.71 +/- 0.05 nmol. cm(-2).second(-1); this process was inhibited (14%) by 10(-5) mol/L 8-bromo-cyclic adenosine monophosphate (cAMP), and increased by 35% with 10(-8) mol/L phorbol ester [phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC)]. During luminal perfusion with 10(-11) mol/L AVP, J(K) increased to 0.88 +/- 0.08 nmol. cm(-2).seconds(-1). In the presence of 10(-11) mol/L AVP, J(K) was not affected by 10(-4) mol/L H89, a blocker of protein kinase A (PKA), but was inhibited (45%) by 10(-5) mol/L staurosporine, an inhibitor of PKC, and by 41% during perfusion with 5 x 10(-5) mol/L of the cell Ca2+ chelator bis (2-aminophenoxy) ethane-tetraacetic acid (BAPTA). In order to study the role of Ca2+-dependent K channels in the luminal hormonal action, the tubules were perfused with 5 mmol/L tetraethylammonium chloride (TEA) or 10(-7) mol/L iberiotoxin, in the presence of AVP, and JK was significantly reduced by both agents. Iberiotoxin reduced AVP-stimulated J(K) by 36.4%, and AVP-independent J(K) (after blocking V1 receptors) by only 16%.Conclusion. The results suggest that the luminal V1-receptor effect of AVP on J(K) was mediated by the phospholipase C (PLC)/ Ca2+/PKC signaling path and not by adenylate cyclase/cAMP/PKA, therefore probably acting on maxi-potassium channels.

2,3-Dihydrobenzofuran neolignans from Aristolochia pubescens

From a hexane extract of stems and roots of Aristolochia pubescens, the new neolignans (2S,3S,1'R,2'R)- and (2S,3S, 1'S,2'R)-2,3-dihydro-5-(1',2'-dihydroxypropyl)-2-(4-hydroxy-3-methylbenzofuran) and (2S,3S,1'R,2'R)- and (2S,3S,1'S,2'R)-2,3-dihydro-5-(1',2'-dihydroxypropyl)-2-(3,4-dimethoxyphenyl)-7-methoxy-3-methyl-benzofuran were isolated, together with the known neolignan licarin A, and its bisnor-neolignan aldehyde and acid derivatives. In addition, sitosterol, 8R,9R-oxide-beta-caryophyllene, kobusone, ent-kauran-16 alpha, 17-diol, vanillin, vanillic acid, (+)-sesamin, (+)eudesmin, and (-)-cubebin were isolated. The structures of the new compounds have been elucidated by spectroscopic methods and by chemical transformation using Mosher's acid chloride. (C) 1999 Elsevier B.V. Ltd. All rights reserved.

Combination of nickel and titanium complexes containing nitrogen ligands as catalyst for polyethylene reactor blending

Ethylene was polymerized using a combination of Ni(diimine)Cl-2 (1) (diimine = 1,4-bis(2,6-di-isopropylphenyl)-acenaphthenediimine) and {Tp(Ms)*} TiCl3 (2) (Tp(Ms)* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesityl-pyrazol-1-yl)) compounds in the presence of methyl-aluminoxane (MAO) at 30 degrees C. The productivity reaches a maximum at X-Ni = 0.75 (1400 kg of PE/mol[M] . h), and the produced polyethylene (PE) showed maximal melt flow index (0.13 g/10 min) and minimal intrinsic viscosity (2.24 dL/g) compared to polyethylenes obtained with different values of nickel loading fractions (X-Ni). Productivity intrinsic viscosity data, as well as melt flow index measurements markedly depend upon the content of the late transition metal, thus suggesting a synergic effect between nickel and titanium catalysts.

Effect of partial preferential orientation and distortions in octahedral clusters on the photoluminescence properties of FeWO4 nanocrystals

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Broadband NIR Emission in Sol-Gel Er(3+)-Activated SiO(2)-Ta(2)O(5) Glass Ceramic Planar and Channel Waveguides for Optical Application

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of different surfactants on the shape, growth and photoluminescence behavior of MnWO4 crystals synthesized by the microwave-hydrothermal method

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Kinetics and mechanism of the forward and reverse reactions between N,N′-dimethyl-4,4′-bipyridinium and hexacyanoferrate(II)

The kinetics of the hexacyanoferrate(III)-N,N′-dimethyl-4,4′-bipyridinium radical (MV+) reaction was studied by a laser flash photolysis technique. The radical was generated, in the presence of Fe(CN)6 3-, by quenching the excited state *Ru(bpy)3 2+ with MV2+. The second-order rate constant for the Fe(CN)6 3--MV+ reaction is (7.6 ± 0.5) × 109 M-1 s-1 at 23°C and ionic strength 0.10 M. Comparison with the rate constants calculated for the diffusion-controlled reaction (4.7 × 109 M-1 s-1) and the activation-controlled reaction (5.2 × 1012 M-1 s-1, on the basis of self-exchange rate constants of 8.0 × 105 M-1 s-1 and 1.9 × 104 M-1 s-1 for the MV2+/+ and Fe(CN)6 3-/4- couples, respectively) leads to the conclusion that the Fe(CN)6 3--MV+ reaction is diffusion controlled. The rate constant for the Fe(CN)6-MV2+ reaction, calculated from the rate constant for the Fe(CN)6 3--MV+ reaction and the appropriate equilibrium constant, is 2.4 × 10-5 M-1 s-1 at 23°C and ionic strength 0.10 M. Microscopic reversibility considerations require that the Fe(CN)6 4--MV2+ reaction be controlled by the dissociation of the successor complex Fe(CN)6 3-|MV+. The thermal and optical electron transfers in the ion pair Fe(CN)6 4-|MV2+ and in related systems are analyzed and discussed. © 1982 American Chemical Society.

Use of one-bottle adhesive as an intermediate bonding layer to reduce sealant microleakage on saliva-contaminated enamel

Purpose: To evaluate the influence of three different adhesives, each used as an intermediary layer, on microleakage of sealants applied under condition of salivary contamination. Materials and Methods: Six different experimental conditions were compared, 3 with adhesives and 3 without. After prophylaxis and acid etching of enamel, salivary contamination was placed for 10 s. In Group SC the sealant was applied after saliva without bonding agent and then light-cured. In Group SCA, after saliva, the surface was air dried, and then the sealant was applied and cured. In Groups ScB, SB and PB, a bonding agent (Scotchbond Dual Cure/3M, Single Bond/3M and Prime & Bond 2.1/Dentsply, respectively) was applied after the saliva and prior to the sealant application and curing. After storage in distilled water at 37°C for 24 hrs, the teeth were submitted to 500 thermal cycles (5°C and 55°C), and silver nitrate was used as a leakage tracer. Leakage data were collected on cross sections as percentage of total enamel-sealant interface length. Representative samples were evaluated under SEM. Results: Sealants placed on contaminated enamel with no bonding agent showed extensive microleakage (94.27% in SC; 42.65% in SCA). The SEM revealed gaps as wide as 20 μm in areas where silver nitrate leakage could be visualized. In contrast, all bonding agent groups showed leakage less than 6.9%. Placement of sealant with a dentin-bonding agent on contaminated enamel significantly reduced microleakage (P< 0.0001). The use of a bonding agent as an intermediary layer between enamel and sealant significantly reduced saliva's effect on sealant microleakage.

The influence of chemical activation on hardness of dual-curing resin cements.

During the cementation of metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. This study evaluated the influence of chemical activation compared with dual-curing (chemical and light activation), on the hardness of four dual-curing resin cements. In a darkened environment, equal weight proportions of base and catalyst pastes of the cements Scotchbond Resin Cement, Variolink II, Enforce and Panavia F were mixed and inserted into moulds with cavities of 4 mm in diameter and 2 mm in height. Subsequently, the cements were: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated (dual-curing = dual-cured groups). The Vickers hardness number was measured at 1 hour, 24 hours and 7 days after the start time of cements' spatulation. For all the cements, the hardness values of self-cured groups were lower than those of the respective dual-cured groups at 1 hour and 24 hours. At 7 days, this behavior continued for Variolink II and Panavia F, whilst for Scotchbond Resin Cement and Enforce there was no statistical difference between the two activation modes. All cements showed a significant increase in their hardness values from 1 hour to 7 days for both activation modes. Of the self-cured groups, Scotchbond Resin Cement and Variolink II presented the highest and the lowest hardness values, respectively, for all three times tested. Within the limitations of this study, up to the time of 24 h, chemical activation alone was unable to promote similar hardness as to that obtained with dual-curing.

Effect of cyclic compressive loading on the bond strength of an adhesive system to dentin after collagen removal

Purpose: The objective of this study was to verify the effect of cyclic compressive loading on the shear bond strength of an adhesive system following collagen removal. Materials and Methods: Sixty bovine teeth were divided into 4 groups based on the adhesive procedure used: groups 1 and 2 - etching with 35% phosphoric acid and application of the Single Bond adhesive system; groups 3 and 4 - after etching, a 10% sodium hypochlorite solution was applied for 1 min before the application of the adhesive. In all the specimens, a Z100 resin cylinder was built up over the bond area. Groups 2 and 4 were submitted to 500,000 cycles with a load of 100 N. Results: The mean values for the shear bond test (MPa) were: group 1: 7.37 ± 1.15; group 2: 5.72 ± 1.66; group 3: 5.95 ± 1.21; group 4: 3.66 ± 1.12. There was no difference between groups 1 and 2 (p > 0.01). Between groups 1 and 3, 2 and 4, and 3 and 4 there was a significant difference (p < 0.01). The majority of the specimens demonstrated an adhesive failure. Conclusion: The application of sodium hypochlorite on dentin decreased the values of shear bond strength, as did the load cycling in the group treated with sodium hypochlorite.

Scanning electron microscope analysis of internal adaptation of materials used for pulp protection under composite resin restorations

Purpose: The aim of this study was to evaluate the interfacial microgap with different materials used for pulp protection. The null hypothesis tested was that the combination of calcium hydroxide, resin-modified glass ionomer, and dentin adhesive used as pulp protection in composite restorations would not result in a greater axial gap than that obtained with hybridization only. Materials and Methods: Standardized Class V preparations were performed in buccal and lingual surfaces of 60 caries-free, extracted human third molars. The prepared teeth were randomly assessed in six groups: (1) Single Bond (SB) (3M ESPE, St. Paul, MN, USA); (2) Life (LF) (Kerr Co., Romulus, MI, USA) + SB; (3) LF + Vitrebond (VT) (3M ESPE) + SB; (4) VT + SB; (5) SB + VT; (6) SB + VT + SB. They were restored with microhybrid composite resin Filtek Z250 (3M ESPE), according to the manufacturer's instructions. However, to groups 5 and 6, the dentin bonding adhesive was applied prior to the resin-modified glass ionomer. The specimens were then thermocycled, cross-sectioned through the center of the restoration, fixed, and processed for scanning electron microscopy. The specimens were mounted on stubs and sputter coated. The internal adaptation of the materials to the axial wall was analyzed under SEM with × 1,000 magnification. Results: The data obtained were analyzed with nonparametric tests (Kruskal-Wallis, p ≤ .05). The null hypothesis was rejected. Calcium hydroxide and resin-modified glass ionomer applied alone or in conjunction with each other (p < .001) resulted in statistically wider microgaps than occurred when the dentin was only hybridized prior to the restoration. ©2005 BC Decker Inc.

The effect of adhesive systems on the pullout strength of a fiberglass-reinforced composite post system in bovine teeth

Purpose: To evaluate the pullout strength of a glass fiber-reinforced composite post (glass FRC) cemented with three different adhesive systems and one resin cement. The null hypothesis was that pullout strengths yielded by the adhesive systems are similar. Materials and Methods: Thirty bovine teeth were selected. The size of the specimens was standardized at 16 mm by sectioning off the coronal portion and part of the root. The specimens were divided into three groups, according to the adhesive system, which were applied following the manufacturers' instructions: G1, ScotchBond Multi-Purpose Plus; G2, Single Bond; G3, Tyrian SPE/One-Step Plus. The glass FRCs (Reforpost) were etched with 37% H3PO4 for 1 min and silanized (Porcelain Primer). Thereafter, they were cemented with the dual resin cement En-Force. The specimens were stored for 24 h, attached to an adapted device, and submitted to the pullout test in a universal testing machine (1 mm/min). The data were submitted to the one-way ANOVA and Tukey's test (α = 0.05). Results: G1 (30.2 ± 5.8 Kgf) displayed the highest pullout strength (p < 0.001) when compared to G2 (18.6 ± 5.8 Kgf) and G3 (14.3 ± 5.8 Kgf), which were statistically similar. Analysis of the specimens revealed that all failures occurred between the adhesive system and the root dentin (pullout of the post cement), regardless of group. Conclusion: The multiple-bottle, total-etch adhesive system provided higher pullout strength of the glass FRC when compared to the single-bottle, total-etch, and single-step self-etching adhesive systems. The null hypothesis was rejected (p < 0.001).

Fatigue resistance of the bond of a glass-infiltrated alumina ceramic to human dentin

Purpose: To evaluate the fatigue resistance of the bond between dentin and glass-infiltrated alumina ceramic, using different luting protocols. Materials and Methods: The null hypothesis is that the fatigue resistance varies with the luting strategy. Forty blocks of In-Ceram Alumina were prepared, and one surface of each block was abraded with 110-μm aluminum oxide particles. Then, the blocks were luted to flat dentin surfaces of 40 human third molars, using 4 different luting strategies (luting system [LS]/ceramic surface conditioning [CSC]) (n=10): (G1) [LS] RelyX-Unicem/[CSC] airborne abrasion with 110-μm Al2O3 particles; (G2) [LS] One-Step + Duo-Link (bis-GMA-based resin)/[CSC] etching with 4% hydrofluoric acid + silane agent; (G3) [LS] ED-Primer + Panavia F (MDP-based resin)/[CSC] Al2O 3; (G4) [LS] Scotchbond1+RelyX-ARC (bis-GMA-based resin)/[CSC] chairside tribochemical silica coating (air abrasion with 30-μm SiO x particles + silane). After 24 h of water storage at 37°C, the specimens were subjected to 106 fatigue cycles in shear with a sinusoidal load (0 to 21 N, 8 Hz frequency, 37°C water). A fatigue survivor score was given, considering the number of the fatigue cycles until fracture. The failure modes of failed specimens were observed in a SEM. Results: G3 (score = 5.9, 1 failure) and G4 (score = 6, no failures) were statistically similar (p = 0.33) and had significantly higher fatigue resistance than G1 (score = 3.9, 5 failures) and G2 (score = 3.7, 6 failures) (p < 0.03). SEM analysis of fractured specimens of G1 and G2 showed that almost all the failures were between ceramic and cement. Conclusion: The MDP-based resin cement + sandblasting with Al2O3 particles (G3) and bis-GMA-based resin cement + tribochemical silica coating (G4), both using the respective dentin bonding systems, were the best luting protocols for the alumina ceramic. The null hypothesis was confirmed.

Measurement of sealant surface area by clinical/computerized analysis: 11-year results.

OBJECTIVE: To analyze the clinical behavior of 2 pit and fissure sealants through clinical/computerized evaluation. METHOD AND MATERIALS: Occlusal sealants were placed on maxillary and mandibular first and second premolars according to a split-mouth design. All premolars were sealed with either Concise (3M Espe) or Prisma Shield (Caulk/Dentsply) sealant agents. A hematoxylin-based staining solution was applied on the occlusal surface 7 days, 18 months, 36 months, and 11 years after occlusal sealing to allow checking of the sealant material on the surface. At each analysis time all occlusal surfaces were photographed, and the photographs corresponding to each time period were analyzed with SigmaScan 4.0 Software. The alterations of the sealed area of each sealant were analyzed with the software and recorded. Next, the measurements of the areas were tabulated and analyzed according to each period. Analysis of variance (ANOVA), with parts subdivided into time, and the t test, with a significance level of 5%, were used. RESULTS: The greatest sealed area was maintained by the sealant Concise. However, over the course of 11 years, all sealants began to show the same level of alteration in sealed area. CONCLUSION: The sealing materials showed alteration in sealed area over time, but they were efficient in controlling caries lesion formation on premolar pits and fissures.