Characterization of the ground state pyrene complex in ethylene-propylene copolymer solutions

Pyrene-labeled functionalized ethylene-propylene (EP) copolymer was prepared by grafting 1-pyrenebutyrylhydrazine onto EP copolymer through maleic anhydride pendants. The EP copolymer contained 60 mol % ethylene; its weight-average molecular weight (M^w) was 148,000. The pyrene-labeled amide functionalized EP copolymer, PA-EP(60/40), was made to simulate the amine functionalized EP copolymers that are commonly used as dispersant additives in motor oils. UV absorption spectra, fluorescence emission and excitation spectra, and fluorescence decay profiles of the pyrene were studied to determine the copolymer conformation and dynamics in methylcyclohexane and tetrahydrofuran (THF). The pyrene fluorescence characteristics of PA-EP(60/40) were highly dependent on the solvent. The dependence of fluorescence emission intensity on the excitation wavelength was large in methylcyclohexane and moderate in THF. A frequency shift of about 2 nm was observed between the excitation spectrum obtained with the emission line at 377 nm and that at 550 nm in the methylcyclohexane solutions, but no shift was found in the corresponding tetrahydrofuran solutions. The ratios of the preexponential factors (a₂₁/a₂₂) of the excimer decays obtained in both methylcyclohexane and THF solutions were different from ?1.0. However, the deviation of the excimer formation process from the Birks scheme is small in THF but large in methylcyclohexane. In addition, the Huggins constants obtained from intrinsic viscosity measurements of the PA-EP(60/40) copolymer solutions suggest that copolymer aggregation occurs in methylcyclohexane but not in THF. H-bonding between two pyrene-containing pendants is apparently the main driving force for the formation of the ground state pyrene complex. THF is found to be effective in inhibiting the H-bonding formation. © 1995 John Wiley & Sons, Inc.     

Environmental degradation of a novel ethylene-propylene copolymer in thick sheets

The outdoor ageing of a commercial ethylene-propylene copolymer (Adflex) is investigated. Different techniques (infrared spectroscopy, thermal analysis, scanning electron microscopy, mechanical tests and positron annihilation lifetime spectroscopy) are used in order to obtain a comprehensive view of the modifications occurring during the environmental ageing of thick sheets of this copolymer. The degradation of the material is ascribed to a morphology variation, arising from the separation of amorphous oxidised copolymers initially dispersed in the bulk of the material. Weathering process takes places with increase of the bulk density of the sample.     

Distribution of functional groups grafted onto an ethylene-propylene copolymer

A theoretical model, based on the binomial (Bernoullian) distribution function, was employed for the prediction of functional group distribution in an ethylene-propylene copolymer randomly grafted by maleic anhydride. Using the experimentally determined graft level and molecular weight distribution function, the fraction of polymer molecules with given number of functional groups was calculated. The result was checked experimentally by a fluorescence method based on the excimer formation of pyrene fluorophores attached to the anhydride pendants. The time-resolved fluorescence from the pyrene-labeled copolymer yielded the fraction of polymer molecules with a single functional group. The fraction of singly labeled molecules was compared to the calculated functional group distribution and a reasonable agreement was found between the two. The distribution of grafted maleic anhydride was found to be apparently random among polymer molecules. The distribution of distances was calculated between randomly attached consecutive functional groups along the polymer backbone also. The result indicated that the distance distribution function (similar to a decaying exponential) is dominated by short distances. © 1996 John Wiley & Sons, Inc.     

Synthesis of copper sulphide and copper nanoparticles with microemulsion method

The present work is focused on the synthesis of nanocopper and nanocopper sulphide metallic particles. The precise control of size and shape is best achievable with microemulsion technique, with in situ synthesis in microemulsion. The effect of most crucial operating parameter, water-to-surfactant molar ratio (w), on the product specification including size as well as size distribution and morphology were investigated. The variation of size was observed with variation in w for copper sulphide and copper. Product specifications were analyzed using transmission electron microscope imaging, dynamic light scattering with particle size analyzer and absorption spectra using UV-visible spectrophotometer. It was observed that bigger particles were achieved at higher water-to-surfactant ratio. From systematic study of effect of w on the size and size distribution of copper nanoparticles, the optimum value was chosen for preparation of in situ catalyst. As copper on alumina catalyst has wide catalytic applications of commercial importance, alumina was selected as support. A novel deposition method is developed successfully to deposit the copper nanoparticles from microemulsion on the support. Thus prepared catalyst was analyzed with UV-visible spectrophotometer and found to contain characteristic peak of copper at 655 nm, indicating proper copper deposition on support. XRD analysis of copper on alumina catalyst confirmed presence of metallic copper.     

Synthesis of size-controlled and shaped copper nanoparticles

The synthesis of stable, monodisperse, shaped copper nanoparticles has been difficult, partially because of copper's propensity for oxidation. This article reports the findings of an investigation of a synthetic route for the synthesis of size-controllable and potentially shape-controllable molecularly capped copper nanoparticles. The approach involved the manipulation of reaction temperature for the synthesis of copper nanoparticles in organic solvents in the presence of amine and acid capping agents. By manipulating the reaction temperature, this route has been demonstrated for the production of copper nanoparticles ranging from 5 to 25 nm. The size dependence of the melting temperature of copper nanoparticles, especially for surface melting, is believed to play an important role in interparticle coalescence, leading to size growth as the reaction temperature is increased. Control of the reaction temperature and capping molecules has also been demonstrated to produce copper nanoparticles with different shapes such as rods and cubes. The previously proposed combination of the selective formation of a seed precursor and a selective growth direction due to the preferential adsorption of capping agents on certain nanocrystal facets is believed to be responsible for shape formation by kinetically controlling the growth rates of crystal facets. The nanoparticles are characterized using TEM, XRD, and UV-visible techniques. A mechanistic consideration of the size control and shape formation is also discussed.     

Synthesis and spectroscopy of CdS nanoparticles in amphiphilic diblock copolymer micelles

Amphiphilic diblock copolymers with the same hydrophilic but different hydrophobic blocks were used as stabilizing agents to prepare cadmium sulfide nanoparticles in aqueous solutions containing 5% of different nonaqueous solvents: methanol, THF, and acetone. Nearly spherical nanoparticles with a fair degree of monodispersity and quantum yields of 1.5%-2% were obtained. Optical absorption band edge of the CdS nanoparticles shows a >0.5 eV blueshift compared to that of bulk CdS, indicating a high degree of quantum confinement. The absorption spectra, while insensitive to the nature of the hydrophobic blocks, exhibited a clear dependence on the nature of the minor, nonaqueous solvents. The photoluminescence in all cases was broad and redshifted, indicating a predominance of surface trap-state emission. Time-resolved photoluminescence demonstrates that the trap states are populated within the first 500 fs, followed by decay with a broad range of time constants from 0.1 to >10 ns, low energy traps decaying at a slower rate than high-energy ones. Time-resolved photoluminescence anisotropy revealed that the nanoparticles experience a local microviscosity very similar to that of bulk water. The experimental observations suggest that nanoparticle formation takes place predominantly in the hydrophilic corona region of the micelles, around specific points with high local concentration of the Cd+2-coordinating basic amine groups of hydrophilic block and/or the minor, nonaqueous solvent component.     

Synthesis of sodium-polystyrenesulfonate-grafted nanoparticles by core-cross-linking of block copolymer micelles

Sodium poly(styrenesulfonate)(polySSNa)-grafted polymer nanoparticles were synthesized by core-cross-linking of block copolymer micelles and subsequent chemical transformation. Block copolymers, poly(p-((1-methyl)silacyclobutyl)styrene-block-poly(neopentyl p-styrenesulfonate)s, polySBS-b-polySSPen, were synthesized by nitroxy-mediated living radical polymerization. The block copolymers formed micelles (R_h=15-23 nm, where R_h represents the hydrodynamic radius) with a polySBS core and polySSPen shell in acetone. The micelle core was cross-linked by ring-opening polymerization of silacyclobutyl groups in polySBS. Hydrolysis of the neopentyl groups provided polySSNa-grafted nanoparticles. The R_h of the particles before the hydrolysis ranged from 12 to 21 nm in acetone, while they varied to the range from 50 to 110 nm in water after the hydrolysis.     

Gamma radiation effects on an amine antioxidant added in an ethylene-propylene copolymer

The aim of this work was to compare the gamma radiation induced effects on samples of an ethylene-propylene copolymer antioxidant free with samples loaded with an antioxidant characterised by the presence of an -NH functional group. The employed techniques were Electron Spin Resonance spectroscopy (ESR) and High Performance Liquid Chromatography (HPLC). Stable radicals R---NO° due to the interaction of free radicals produced in the irradiated polymer with the antioxidant have been observed by ESR at room temperature. The time evolution of the ESR signals following the irradiation was examined at different doses. The amount of antioxidant not involved in the oxidation reactions has been determined using HPLC.     

Synthesis of iron oxide nanoparticles in a polyimide matrix

A monolayer of gamma-Fe(2)O(3) nanoparticles embedded in a polyimide (PI) matrix was fabricated by oxidizing an Fe metal film between two PI precursor layers. There was a critical Fe thickness ( approximately 7 nm) above which a continuous layer of gamma-Fe(2)O(3) film was formed in the PI film. Below the critical Fe thickness, the oxide film broke up into fine particles whose size was approximately 8 nm with narrow size distribution. It was further shown that these nanoparticles could have metallic cores, surrounded by an oxide layer. This method offers a unique way of covering a large surface area with fine magnetic oxide nanoparticles for potential application in high-density data-storage media.     

Synthesis of copper nanoparticles stabilized by polyoxyethylenesorbitan monooleate

We studied the influence of synthesis parameters and the composition of the reaction mixture on the size and morphology of copper nanoparticles (NPs). Use of a surfactant (polyoxyethylenesorbitan monooleate) is promising for confining NP growth and stabilizing NPs. Concentration ranges of existence were determined for copper NP dispersions stable to aggregation and sedimentation. Scanning electron microscopy and dynamic light scattering were used to show that: the NP size varied from 10 to 65 nm, the average diameter was 25–35 nm, and the shape was spherical. The sizes of copper NP aggregates were determined.     

Synthesis of metallic copper nanoparticles coated with polypyrrole

This paper describes a method for polypyrrole (PPy) coating of metallic Cu nanoparticles in aqueous solution in atmosphere. Colloid solution of Cu nanoparticles was prepared by reducing Cu ions with the use of hydrazine in an aqueous solution dissolving citric acid and cetyltrimethylammonium bromide as stabilizers. The PPy coating was performed by polymerizing pyrrole with the use of hydrogen peroxide as an initiator in an aqueous colloid solution of the Cu nanoparticles. Ultraviolet–visible extinction measurements, transmission electron microscopy observation, and X-ray diffraction measurements revealed that the metallic Cu nanoparticles with a size of 27.6 ± 11.1 nm were coated with PPy. The obtained PPy-coated Cu particles were chemically stable even in atmosphere.     

Synthesis and characterization of copper nanoparticles by reducing agent

Cu nanoparticles were synthesized by solution reduction process successfully. The influence of parameters on the size of Cu nanoparticles was studied and the referential process parameters were obtained. The morphology and structure of the synthesized Cu nanoparticles were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), QELS data, infrared spectroscopy (IR) and solid state UV. The average size of nanoparticles was found between 15 ± 2 nm.     

Chemical inequivalence behavior of the protons attached to the same carbon in ethylene-propylene copolymer（EPC）

Six ethylene-propylene copolymer samples with different structural parameters were analyzed by ^1H NMR,^13C NMR and ^1H-^13C COSY in this paper.With the aid of the ^1H-^13C COSY spectra of ethylene-propylene copolymer,the chemical inequivalence behavior of the protons attached to the same carbon in the ethylene-propylene copolymer could be observed. Four basic types of chemical bonds were divided,and two kinds of main conformations were proposed to explain this phenomenon. Based on the calculation of conformation distribution,it can be proved that the explanation of this phenomenon was reasonable.     

Toughening of ethylene-propylene random copolymer/clay nanocomposites: Comparison of different compatibilizers

Ethylene/propylene-random-copolymer(PPR)/clay nanocomposites were prepared by two-stage melt blending. Four types of compatibilizers,including an ethylene-octene copolymer grafted maleic anhydride(POE-g-MA) and three maleic-anhydride-grafted polypropylenes(PP-g-MA) with different melt flow indexes(MFI),were used to improve the dispersion of organic clay in matrix.On the other hand,the effects of organic montmorillonite(OMMT) content on the nanocomposite structure in terms of clay dispersion in PPR matrix,thermal behavior and tensile properties were also studied. The X-ray diffraction(XRD) and transmission electron microscopy(TEM) results show that the organic clay layers are mainly intercalated and partially exfoliated in the nanocomposites.Moreover,a PP-g-MA compatibilizer(compatibilizer B) having high MFI can greatly increase the interlayer spacing of the clay as compared with other compatibilizers.With the introduction of compatibilizer D(POE-g-MA),most of the clays are dispersed into the POE phase,and the shape of the dispersed OMMT appears elliptic,which differs from the strip of PP-g-MA.Compared with virgin PPR,the Young’s modulus of the nanocomposite evidently increases when a compatibilizer C(PP-g-MA) with medium MFI is used.For the nanocomposites with compatibilizer B and C,their crystallinities(X_c) increase as compared with that of the virgin PPR. Furthermore,the increase of OMMT loadings presents little effect on the melt temperature(T_m) of the PPR/OMMT nanocomposites,and slight effect on their crystallization temperature(T_c).Only compatibilizer B can lead to a marked increases in crystallinity and T_c of the nanocomposite when the OMMT content is 2 wt%.     

Synthesis and characterization of CdS nanoparticles embedded in a polymethylmethacrylate matrix

CdS nanopowder capped with sodium bis(2-ethylhexyl)sulfosuccinate was synthesized by using water-in-oil microemulsions. The CdS nanoparticles of about 5 nm obtained were embedded in polymethylmethacrylate matrix by a photocuring process. The transparent yellow solid compound was characterized by optical absorption and emission spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The properties of this compound were compared with those of the nanopowder dispersed in heptane and in methylmethacrylate. The results obtained indicate that the nanoparticles are homogeneously dispersed in the matrix and do not change in size during the embedding process. Even if the surface slightly changes its luminescence properties, as a consequence of the different new chemical environment, the final product seems to be suitable for practical applications.     

Synthesis and characterization of metallic copper nanoparticles via thermal decomposition

Copper oxalate was used as a precursor to prepare metallic copper nanoparticles by thermal decomposition. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. XRD analysis revealed broad pattern for fcc crystal structure of copper metal. The particle size by use of Debye–Scherrer’s equation was calculated to be about 40 nm.     

Magnetic nanoparticles supported copper catalysts: Synthesis of heterocyclic scaffolds

Abstract

Heterocyclic scaffolds are important components in the structure of many drugs and natural products. They are well-known compounds because of their broad spectrum of pharmaceutical and biological activities. In this paper, we provide an overview of the utilization of copper complexes immobilized on magnetic nanoparticles as economical and efficient catalytic systems for the synthesis of heterocyclic molecules.     

Physical characterization of blends of isotactic poly(butene-1) with ethylene-propylene copolymer

Melt-mixed blends of isotactic poly(butene-1) (PB) with an ethylene-propylene copolymer (EPM) containing 60 wt% PP were studied over the complete composition range. Phase-contrast polarizing microscopy and dynamic mechanical spectroscopy revealed that the blend is heterogeneous. DSC studies of quenched and annealed blends for both PB modifications indicate that total blend crystallinity decreases linearly with the EPM content. Pure PB crystallinity is enhanced to a small degree in the presence of EPM. Tensile behaviour of the blends was good up to moderate EPM levels. It was also demonstrated that blends containing EPM with increased PP content showed synergism in tensile behaviour not exhibited by blends with EPM of lower PP content. Appropriate mechanical models tested over the complete composition and temperature range suggest that the rubbery phase adheres strongly to the PB matrix. Overall, the experimental results support the contention that the system is mechanically compatible, possibly a result of component miscibility at elevated temperatures as predicted on thermodynamic grounds.     

Synthesis of silicon nitride based ceramic nanoparticles by the pyrolysis of silazane block copolymer micelles

Diblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene (polyVSA‐b‐polySt) and triblock copolymer poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane)‐block‐polystyrene‐block‐poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA‐b‐polySt‐b‐polyVSA), consisting of silazane and nonsilazane segments, were prepared by the living anionic polymerization of 1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane and styrene. PolyVSA‐b‐polySt formed micelles having a poly(1,1,3,N,N′‐pentamethyl‐3‐vinylcyclodisilazane) (polyVSA) core in N,N‐dimethylformamide, whereas polyVSA‐b‐polySt and polyVSA‐b‐polySt‐b‐polyVSA formed micelles having a polyVSA shell in n‐heptane. The micelles with a polyVSA core were core‐crosslinked by UV irradiation in the presence of diethoxyacetophenone as a photosensitizer, and the micelles with a polyVSA shell were shell‐crosslinked by UV irradiation in the presence of diethoxyacetophenone and 1,6‐hexanedithiol. These crosslinked micelles were pyrolyzed at 600 °C in N₂ to give spherical ceramic particles. The pyrolysis process was examined by thermogravimetry and thermogravimetry/mass spectrometry. The morphologies of the particles were analyzed by atomic force microscopy and transmission electron microscopy. The chemical composition of the pyrolysis products was analyzed by X‐ray fluorescence spectroscopy and Raman scattering spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4696–4707, 2006