Molecular Weight (molecular + weight)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Molecular Weight

  • apparent molecular weight
  • average molecular weight
  • controlled molecular weight
  • different molecular weight
  • entanglement molecular weight
  • experimental molecular weight
  • high molecular weight
  • highest molecular weight
  • increasing molecular weight
  • kda molecular weight
  • low molecular weight
  • lower molecular weight
  • moderate molecular weight
  • molecular weight molecular weight
  • number average molecular weight
  • number-average molecular weight
  • polymer molecular weight
  • predictable molecular weight
  • predicted molecular weight
  • same molecular weight
  • similar molecular weight
  • theoretical molecular weight
  • various molecular weight
  • varying molecular weight
  • viscosity-average molecular weight
  • weight average molecular weight
  • weight molecular weight
  • weight-average molecular weight
  • weight-average molecular weight molecular weight

  • Terms modified by Molecular Weight

  • molecular weight average
  • molecular weight bands
  • molecular weight complex
  • molecular weight compound
  • molecular weight control
  • molecular weight cut-off
  • molecular weight determination
  • molecular weight development
  • molecular weight distribution
  • molecular weight dna
  • molecular weight fraction
  • molecular weight heparin
  • molecular weight increase
  • molecular weight measurement
  • molecular weight molecular weight
  • molecular weight organic acid
  • molecular weight poly
  • molecular weight polyethylene
  • molecular weight polymer
  • molecular weight protein
  • molecular weight range
  • molecular weight substance

  • Selected Abstracts


    ABSTRACT Foods containing barley or oats are often marketed as healthy because of the dietary fiber (1,3) (1,4)-,-D-glucan. Processing conditions can affect the molecular structure of these dietary fibers, which in turn affect quality and properties of the products. In this study, the effect of puffing and jet cooking conditions on changes in the solubility and molecular weight of barley ,-glucans was investigated. Barley flour was processed in a pasta extruder to produce particles similar in size and shape to rice. These particles were puffed at 230, 250 and 270C for 6, 8 and 10 s in a rice cake machine. Solubility and molecular weight of barley ,-glucans were determined by using water extracts (25 or 65C). The amount of ,-glucan extracted in water at 25C increased from 41.1% in cakes puffed at 230C/6 s to 69.7% in cakes puffed at 270C/10 s. The amount of ,-glucan extracted in water at 65C increased from 63.6% in samples puffed at 230C/6 s to 99.1% in samples puffed at 270C/10 s. The molecular weight of ,-glucans in barley was reduced by puffing and jet cooking treatments. [source]


    JOURNAL OF PHYCOLOGY, Issue 2 2008
    Peggy Vauchel
    Alginates are natural polysaccharides that are extracted from brown seaweeds and widely used for their rheological properties. The central step in the extraction protocol used in the alginate industry is the alkaline extraction, which requires several hours. In this study, a significant decrease in alginate dynamic viscosity was observed after 2 h of alkaline treatment. Intrinsic viscosity and average molecular weight of alginates from alkaline extractions 1,4 h in duration were determined, indicating depolymerization of alginates: average molecular weight decreased significantly during the extraction, falling by a factor of 5 between 1 and 4 h of extraction. These results suggested that reducing extraction time could enable preserving the rheological properties of the extracted alginates. [source]

    Influence of Molecular Weight on the Performance of Organic Solar Cells Based on a Fluorene Derivative

    Christian Mller
    Abstract The performance of organic photovoltaic (OPV) bulk-heterojunction blends comprising a liquid-crystalline fluorene derivative and a small-molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, Mn,,,10,kg,mol,1, but is rendered less chain-length dependent for higher Mn as the fluorene derivative gradually adopts polymeric behavior. [source]

    Influence of Molecular Weight on Physical and Mechanical Properties of Linear Symmetric S-(S/B)-S Triblock Copolymers

    Mahendra Thunga
    Abstract Symmetric linear S-(S/B)-S triblock copolymers with 80 wt.-% of PS having a block composition of 20-60-20 and a S/B ratio of 70:30 in the middle block are studied with varying molecular weights (). Increase in the leads to a change in the morphology from disordered to ordered microphase separated structure, as characterised by TEM and SAXS. Two distinct glass transitions for PS- and PB-rich phases are observed from DMA measurements, which are due to phase separation at high . Rheological studies (master curves) reveal an extended rubbery plateau and a delay in the terminal response with an increase in , whereas a terminal flow behaviour is observed for materials having a disordered nature at low . A brittle-to-tough transition is observed from tensile tests with the increase in . [source]

    Hydrodynamic Size and Electrophoretic Mobility of Poly(styrene sulfonate) versus Molecular Weight,

    Ute Bhme
    Abstract The effective charge of a macromolecule in solution is significantly smaller than the nominal charge, derived form the number of charged groups and the degree of dissociation. It is reduced by counterion condensation, shielding a considerable fraction of the macromolecules charge. As an example the influence of the molecular weight on hydrodynamic size and electrophoretic mobility of poly(styrene sulfonate) has been investigated. While from diffusion the hydrodynamic size is inferred, in a combination with electrophoresis NMR the effective charge is calculated. At low molecular weight the effective charge is equal to the nominal charge, in an intermediate range the effective charge is that predicted from counterion condensation theory, while at higher molecular weights it becomes considerably smaller. [source]

    Liquid-Glassy Polymer Diffusion: Effects of Liquid Molecular Weight and Temperature

    J. Pablo Tomba
    Abstract We examine mechanistic aspects of the diffusion between a series of liquid polystyrenes (PS) and a glassy poly(phenylene oxide) (PPO) matrix, through the use of confocal Raman microspectroscopy. The results show that the diffusion kinetics has Fickean characteristics, similar to those found in liquid-liquid polymer diffusion. No signatures of the linear regime typical of the case-II diffusion mechanism were found. Overall, these observations are consistent with the claim that case-II is unlikely to occur in liquid-glassy polymer diffusion. [source]

    Crystallization of Poly(, -caprolactone)/Poly(vinyl chloride) Miscible Blends Under Strain: The Role of Molecular Weight

    Yubao Zhang
    Abstract Summary: The effect of poly(, -caprolactone) (PCL) molecular weight on the orientation of crystalline PCL in miscible poly(, -caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by a combination of wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) studies. An unusual crystal orientation with the b-axis parallel to the stretching direction was observed in miscible PCL/PVC blends with PCL of high molecular weight (>21,000). SAXS showed the presence of nanosize confined PCL in the PCL/PVC blends, which could be preserved at temperatures higher than the Tm of PCL but lower than the Tg of PVC. A mechanism based on the confinement of PCL crystal growth was proposed, which can explain the formation of b-axis orientation in PCL/PVC blends crystallized under strain. SAXS pattern of stretched PCL/PVC blend after annealing at 90,C for 5 min. [source]

    Effect of Chain Straightening on Plateau Modulus and Entanglement Molecular Weight of Ni-diimine Poly(1-hexene)s

    Zhibin Ye
    Abstract Summary: In this communication, we report the first rheological study on the chain-straightened Ni-diimine poly(1-hexene)s and investigate the unique effect of chain straightening on plateau modulus and entanglement molecular weight of this series of polymers. Two Ni-diimine poly(1-hexene) samples having different levels of chain straightening were prepared with a chain-walking Ni-diimine catalyst, (ArNC(An)C(An)NAr)NiBr2 (An,=,acenaphthene, Ar,=,2,6-(i -Pr)2C6H3) at two different temperatures. Rheological analyses show that the chain-straightened polymers exhibit significantly enhanced plateau modulus and reduced entanglement molecular weight compared to regular poly(1-hexene)s by metallocene catalysis. Such an effect becomes more pronounced with an increase in the level of chain straightening. Loss moduli G,(,) versus reduced angular frequency in a linear, natural logarithm plot for the three polymers at the reference temperature of 100,C. [source]

    Effect of Molecular Weight on Photoinduced Birefringence in a Chiral Liquid Crystalline Azodye Polymer

    Mikhail Kozlovsky
    Abstract Summary: The evolution of the photoinduced birefringence in thin films of narrow polymer fractions is studied and compared with the behavior of the non-fractionated polymer. The ,nind value decreases by increasing the degree of polymerization () within the oligomeric range but becomes independent of molecular weight starting from a of ,70. Thermal pretreatment of the films results in higher photoinduced birefringence. The films show good stability of the photorecording. Birefringence induced after 10 min, ,nind(600) and its growth rate at the same moment versus molecular weight. [source]

    Study on Flow Induced Nano Structures in iPP with Different Molecular Weight and Resulting Strength Behavior

    Achim Frick
    Abstract Polypropylene samples in a wide molecular weight range between approx. 100,kg/mol to 1 600,kg/mol were processed by injection molding to thin walled micro specimens with respect to study shear induced crystallization phenomena under high shear rate and subsequently possible self reinforcement effects. The specimens nano structures were investigated and related deformation behavior under tensile studied. Novel morphologies have been detect and their micromechanical mechanism interpret and summarized. [source]

    Poly(L -lactide) Nano- and Microfibers by Electrospinning: Influence of Poly(L -lactide) Molecular Weight

    Waclaw Tomaszewski
    Abstract Summary: The electrospinning technique based on single and multi-jet systems was applied for poly(L -lactide) (PLA) nano- and microfibers as well as fibrous mats manufacture; the latter with dimensions suitable for the tensile tests. The PLA's employed were prepared by the controlled ring-opening polymerization of the L,L -lactide (LA) monomer. The resulting fibers thickness was correlated with molecular weights of PLA's and viscosities of spinning solutions. The scanning electron microscopic, thermal, and tensile characteristics of the polymeric materials and fibrous mats were also examined. [source]

    On the Production of Polyolefins with Bimodal Molecular Weight and Copolymer Composition Distributions in Catalytic Gas-Phase Fluidized-Bed Reactors

    Christos Chatzidoukas
    Abstract A comprehensive mathematical model is developed for the dynamic calculation of the molecular distributed properties (i.e. MWD and CCD) in a gas-phase, catalytic, ethylene-1-butene copolymerization, FBR, taking into account the various kinetic, micro- and macroscopic phenomena in the reactor. The effects of the two single-site catalyst mass fractions and reactor operating conditions on the production of polyolefins with ,tailor-made' bimodal molecular properties are investigated. It is shown that PE grades with either a bimodal MWD or CCD can be produced in a single FBR, using a mixture of two single-site catalysts under properly selected operating conditions. [source]

    Antibacterial Activities of Chitosans and Chitosan Oligomers with Different Molecular Weights on Spoilage Bacteria Isolated from Tofu

    H.K. No
    ABSTRACT Seven bacteria were isolated from spoiled tofu and identified as Bacillus sp. (S08), B. megaterium (S10), B. cereus (S17, S27, S28, S32), and Enterobacter sakazakii (S35). In a paper disc test with 6 chitosans and 6 chitosan oligomers of different molecular weights, chitosans showed higher antimicrobial activity than did chitosan oligomers at a 0.1% concentration. Results of inhibitory effects of 6 chitosans on growth of Bacillus sp. (S08) failed to detect viable cells after incubation for 24 hrs at 37 C, even at 0.02% concentration. With B. megaterium (S10) and B. cereus (S27), a 3 to 4 log cycle reduction was found in the chitosan-treated group. The growth of Enterobacter sakazakii (S35) was completely suppressed in the presence of 0.04% chitosan except for 1 chitosan product. The minimum inhibitory concentration of chitosan differed with products and isolates, ranging from 0.005% to above 0.1%. [source]

    Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular Weights

    Claudia Stern
    Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source]

    Molecular weight and humification index as predictors of adsorption for plant- and manure-derived dissolved organic matter to goethite

    T. Ohno
    Summary Sorptive retention of organic matter is important in maintaining the fertility and quality of soils in agricultural ecosystems. However, few sorption studies have been conducted that use dissolved organic matter (DOM) characteristic of agricultural amendments. We investigated the sorption to goethite (,-FeOOH) of DOM extracted from: (i) above-ground biomass of wheat straw (Triticum aestivum L.), maize residue (Zea mays L.), soybean residue (Glycine max (L.) Merr.), and hairy vetch residue (Vivia billosa L.); (ii) below-ground biomass from maize, soybean, canola (Brassica napus L.), and green bean (Phaseolus vulgaris L.); and (iii) beef, dairy, poultry, and pig animal manures. The apparent molecular weight (MWAP) of the DOM was measured by high performance-size exclusion chromatography and ranged from 312 to 1074 g mol,1. The carboxyl-group content of the DOM measured by potentiometric titration ranged from 4.84 to 21.38 mmol(,) g,1 carbon. The humification index (HIX) determined by fluorescence spectrometry varied from 1.15 to 4.33. Sorption was directly related to both MWAP and HIX values of the DOM. Molecular weight analysis of the solution prior to and after sorption indicated that the DOM molecules > 1800 g mol,1 were preferentially sorbed, resulting in fractionation of the DOM upon reaction with goethite. The multiple regression equation, based only on MWAP and HIX parameters, explained 76% of the variance in amount of DOM sorbed. The results indicate that MWAP and HIX are important factors in controlling the sorption of DOM to mineral surfaces. Amendment with materials that release DOM of higher molecular weight and greater humification will result in enhanced initial sorption of DOM to soil solids, thereby contributing to accumulation of a larger soil organic C pool. [source]

    A QSAR analysis of toxicity of Aconitum alkaloids

    Anglica M. Bello-Ramrez
    Abstract Biological activity of Aconitum alkaloids may be related to their toxicity rather than to a specific pharmacological action. A Quantitative structure-activity relationships (QSAR) analysis was performed on the following two groups of alkaloids: compounds with an aroyl/aroyloxy group at R14 position (yunaconitine, bulleyaconitine, aconitine, beiwutine, nagarine, 3-acetyl aconitine, and penduline), and compounds with the aroyloxy group at R4 position (N -deacetyllappaconitine, lappaconitine, ranaconitine, N -deacetylfinaconitine, N -deacetylranaconitine). The LD50 (,mol/kg) of the 12 alkaloids were obtained from the literature. LD50 was significantly lower in group 1 than in group 2. The steric and core,core repulsion energies were significantly higher in group 1. The total energy and heat of formation and electronic energies were significantly lower in group 1. The reactivity index of N, C1,, C4, and C6, were similar between groups. The reactivity index of C2, was significantly higher and the reactivity index of C3, and C5, were significantly lower in group 1. Log P and pKa were similar between groups. Molecular weight was significantly higher in group 1. A significant linear relationship was observed between log LD50 and either analgesic log ED50 or local anesthetic log ED50. The LD50/analgesic ED50 obtained from average values was 5.9 for group 1 and 5.0 for group 2. However, the LD50/local anesthetic ED50 was 40.4 and 318, respectively. The study supports that the analgesic effects of these alkaloids are secondary to their toxic effects whereas alkaloids from group 2 are susceptible to be further studied as local anesthetic agents. [source]

    Isolation and characterization of a protease from Pseudomonas fluorescens RO98

    R. Koka
    Pseudomonas fluorescens RO98, a raw milk isolate, was inoculated into McKellar's minimal salts medium and incubated at 25 C for 48 h to allow production of protease. A zinc-metalloacid protease was purified from the cell-free concentrate by anion exchange and gel filtration chromatography. The purified protease was active between 15 and 55 C, and pH 45 and 90, and was stable to pasteurization. The enzyme had pH and temperature optima for activity of 50 and 35 C, respectively. It was heat stable with a D55 of 41 min and a D625 of 18 h. Molecular weight of the enzyme was estimated to be 52 kDa by SDS PAGE and size exclusion chromatography. Values for kM of 14428, 1873, 11020 and 3523 mol were obtained for whole, ,-, ,- and ,-casein, with a Vmax of 826, 009, 042 and 070 mol mg,1 min,1, respectively. The enzyme hydrolysed ,-casein preferentially when incubated with artificial casein micelles. [source]

    The substituent effects on the structure and surface morphology of polyaniline

    Mutlu Sahin
    Abstract In this work, poly(2-fluoroaniline), poly(2-chloroaniline), poly(2-methylaniline), and poly(N -ethylaniline) were prepared by a self-assembly method using an oxidizing system consisting of a dopant anion, p-toluene sulfonate with ammonium peroxydisulfate. The effects of substituents on the surface morphology, conductivity, molecular weight, spectral and thermal properties of the polymers were studied. SEM results revealed that the surface morphology of the resulting polymers changed from nanofiber to spherical structure by changing the substituent on the aniline monomers. The structure and properties of these conducting films were characterized by FTIR, UV-vis, elemental analysis, TGA, conductivity, and cyclic voltammetry. The polymer films show electroactivity in monomer free solution. Molecular weight of the polymers was determined by gel permeation chromatography. The dry electrical conductivity values of the substituted-polyanilines were found to be lower than that of PANI. The results revealed that the molecular structures of the polymers were similar to those of the emeraldine form of polyaniline. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

    Hydrolytic degradation of poly(ethylene terephthalate)

    Seyed Saeid Hosseini
    Abstract Molecular weight is an important factor in the processing of polymer materials, and it should be well controlled to obtain desired physical properties in final products for end-use applications. Degradation processes of all kinds, including hydrolytic, thermal, and oxidative degradations, cause chain scission in macromolecules and a reduction in molecular weight. The main purpose of this research is to illustrate the importance of degradation in the drying of poly(ethylene terephthalate) (PET) before processing and the loss of weight and mechanical properties in textile materials during washing. Several techniques were used to investigate the hydrolytic degradation of PET and its effect on changes in molecular weight. Hydrolytic conditions were used to expose fiber-grade PET chips in water at 85C for different periods of time. Solution viscometry and end-group analysis were used as the main methods for determining the extent of degradation. The experimental results show that PET is susceptible to hydrolysis. Also, we that as the time of retention in hydrolytic condition increased, the molecular weight decreases, but the rate of chain cleavage decreased to some extent, at which point there was no more sensible degradation. The obtained moisture content data confirmed the end-group analysis and viscometry results. Predictive analytical relationships for the estimation of the extent of degradation based on solution viscosity and end-group analysis are presented. 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2304,2309, 2007 [source]



    ABSTRACT Cyclodextrin glucanotransferases (EC (CGTase) are industrially important enzymes for production of cyclodextrin (CD) from starch. ,-CD yield of CGTase from alkalophilic Bacillus species is usually much lower than ,-CD, while from alkalophilic Bacillus sp. 7-12. ,-CD yield is close to ,-CD. A CGTase from alkalophilic Bacillus sp. 7-12 was purified and characterized. When purified by ammonium sulfate fractionation, DEAE-cellulose column chromatography and Sepharose CL-6B column chromatography, the enzyme obtained consisted of a single band that did not dissociate into subunits by SDS polyacrylamide gel electrophoresis. Molecular weight of the purified enzyme was determined to be 69,000 Da by SDS-PAGE. The enzyme showed a Kmof 1.24 mg/mL and Vmax0.101 M/min when potato starch was used as substrate. The enzyme was stable below 70C with an optimum activity at 60C, and stable at pH range 6,10 with an optimum pH at 8.5. The enzyme activity was strongly inhibited by Ag+, Cu2+, Mg2+, Al3+, Co2+, Zn2+, Fe2+and slightly inhibited by Sn2+, Mn2+. The ions Ca2+and K+, EDTA and DTT had no influence on the enzyme activity. [source]

    Polyphenol Oxidase from Apple (Malus domestica Borkh. cv Bramley's Seedling): Purification Strategies and Characterization

    Deirdre M. Ni Eidhin
    ABSTRACT Polyphenol oxidase (PPO) was isolated from Bramley's Seedling apples with 75.7-fold purification and 26.5% recovery by ammonium sulfate precipitation, phenyl sepharose chromatography, ion exchange chromatography, and hydroxyapatite chromatography. Molecular weight was estimated to be about 45 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS PAGE). Optimum PPO activity was at pH 6.5 and greater than 50% activity was retained during storage for 72 h at pH 5.5 to 6.5. Optimum temperature for activity was 30 C and the enzyme had residual activity of greater than 50% during storage for 72 h at 20 C to 30 C and for 24 h at 40 C to 50 C. Of the substrates tested, activity was greatest with 4-methylcatechol followed by catechol, pyrogallol, and (,)epicatechin. The most effective inhibitors tested were sodium metabisulfite and ascorbic acid. [source]

    Photostabilization of styrene,ethylene,butylene,styrene block copolymer by hindered phenol and phosphite antioxidants

    Cristina Luengo
    The photostabilization of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS), by hindered phenols and their combination with phosphite antioxidants has been studied by using a variety of spectroscopic methods including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The addition of a hindered phenol was found to photostabilize the SEBS in terms of the inhibition of discoloration, and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Strong synergism was found with combinations of a hindered phenol and phosphite antioxidant, especially with an increase in the phosphite concentration. Residual titanium traces present as impurities in the material were found to play an important role in the photo-oxidation of SEBS. Molecular weight appeared to be a determining factor in the proportion of chain scission/crosslinking reactions that occured. Nevertheless, the addition of antioxidants and the reduction of titanium content also proved satisfactory in stabilizing the low-molecular-weight material. J. VINYL. ADDIT. TECHNOL. 12:2,7, 2006. 2006 Society of Plastics Engineers [source]

    Molecular weight of guar gum affects short-chain fatty acid profile in model intestinal fermentation

    Maria L. Stewart
    Abstract Dietary fiber exerts many beneficial physiological effects; however, not all types of dietary fiber display the same effects. Partially hydrolyzed guar gum (PHGG), a lower molecular weight form of guar gum, is more easily incorporated into food, but may have less pronounced physiological effects than the native form. The aim of this study was to identify differences in intestinal fermentability based on the molecular weight of guar gum. Guar gum of four molecular masses (15, 20, 400, and 1100 kDa) was fermented using a batch in vitro fermentation system. Human fecal inoculum was the source of microbes. The 400-kDa fraction produced the greatest concentrations of total short-chain fatty acid (SCFA) at 8 h and the highest amounts of butyrate at 24 h. At 24 h, the 400-kDa fraction produced more total SCFA and propionate than the 15 kDa, but was not different than 20 kDa or 1100 kDa fractions. The molecular weight of guar gum was positively correlated with acetate production and negatively correlated with propionate production. This study concludes that 400-kDa guar gum may be optimal for intestinal fermentability. In conclusion, the molecular weight of guar gum affects in vitro fermentability and should be considered when adding to a food or beverage. [source]

    Speciation of essential and toxic elements in edible mushrooms: size-exclusion chromatography separation with on-line UV,inductively coupled plasma mass spectrometry detection

    Rodolfo G. Wuilloud
    Abstract Size-exclusion liquid chromatography was coupled to UV and inductively coupled plasma mass spectrometry (ICP-MS) for detection to perform elemental speciation studies on different edible mushrooms. Molecular weight (MW) distribution patterns of several elements among different fractions present in various edible mushrooms are presented. The association of the elements with the high and low MW fractions was observed using sequential detection by UV and ICP-MS. Separation was performed using a Superdex 75 column. Variability of the fractionation patterns with three different extraction media (0.05 mol l,1 NaOH; 0.05 mol l,1 HCl; hot water at 60C) was evaluated for mushroom species. A comparative elemental speciation study was performed in order to determine the differences in the fractionation patterns of silver, arsenic, cadmium, mercury, lead, and tin in Boletus edulis, Agaricus bisporus, and Lentinus edodes. Differences in the fractionation patterns of the elements were found to depend on the mushroom species and the extraction medium. Most of the elements were associated with high mw fractions. It was not possible to assess the trace metal contributions from the mushroom growth media. Copyright 2004 John Wiley & Sons, Ltd. [source]

    Synthesis and characterization of amphiphilic biodegradable poly(glutamic acid- co -lactic acid- co -glycolic acid) by direct polycondensation

    Dedai Lu
    Abstract Poly(glutamic acid- co -lactic acid- co -glycolic acid) (PGLG), an amphiphilic biodegradable copolymer, was synthesized by simply heating a mixture of L -glutamic acid (Glu), DL -lactic acid, and glycolic acid with the present of stannous chloride. The unique branched architecture comprising of glutarimide unit, polyester unit, and polyamide unit was confirmed by NMR spectrum. The PGLG was soluble in many organic solvents and aqueous solution of sodium hydroxide (pH , 9.0). The thermal properties were evaluated using thermogravimetric analysis and differential scanning calorimetry. Molecular weights were determined by 1H NMR end-group analysis and GPC, respectively, and the results indicated that the higher Glu content resulted in a decrease of the molecular weight. 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Free-radical copolymerization of 2,2,2-trifluoroethyl methacrylate and 2,2,2-trichloroethyl ,-fluoroacrylate: Synthesis, kinetics of copolymerization, and characterization

    Jean-Marc Cracowski
    Abstract Copolymers based on 2,2,2-trifluoroethyl methacrylate (MATRIFE) and 2,2,2-trichlororoethyl ,-fluoroacrylate (FATRICE) were synthesized in good yields by radical process initiated by tert -butyl 2,2-dimethylperoxypropanoate. Molar composition of the obtained poly(MATRIFE- co -FATRICE) copolymers were assessed by means of 1H and 19F nuclear magnetic resonance spectroscopy and by elemental analysis. The reactivity ratios, ri, of both comonomers were determined from the Kelen-Tdos and Finneman-Ross methods (rMATRIFE = 1.52 0.03 and rFATRICE = 0.61 0.03 at 74 C) showing unexpectedly that MATRIFE is the more reactive monomer in copolymerization. Molecular weights and polydispersity indexes of poly(MATRIFE- co -FATRICE) copolymers were ranging between 1.47 and 2.68 104 gmol,1 and from 1.44 to 2.21, respectively. Thermal properties of the resulting polymers were examined and thermogravimetric analyses showed a satisfactory thermal stability, a thermal decomposition occurring from 220 to 295 C as the molar ratio of FATRICE increased in the copolymer. Moreover, the glass transition temperatures of copolymers varied from 66 to 108 C and also increased with FATRICE molar ratio in the copolymers. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2154,2161, 2010 [source]

    Ferrocenyl-functionalized long chain branched polydienes

    Frederik Wurm
    Abstract A convenient two-step approach for the synthesis of ferrocenyl-functionalized long chain branched polydienes, based on both butadiene and isoprene, respectively, is presented. Classical living anionic polymerization was used to synthesize different ABn type poly(diene) macromonomers with moderate molecular weights between 1700 and 3200 g/mol and narrow polydispersity. Quantitative end-capping with chlorodimethylsilane resulted in the desired ABn macromonomer structures. In the ensuing Pt-catalyzed hydrosilylation polyaddition, branched, functionalized polydienes were obtained by a concurrent ABn + AR type of copolymerization with mono- and difunctional ferrocenyl silanes (fcSiMe2H or fc2SiMeH). Molecular weights of the branched polymers were in the range of 10,000 to 44,000 g/mol (SEC/MALLS). Because of the large number of functional end groups, high loading with ferrocene units up to 63 wt % of ferrocene was achieved. Detailed studies showed full conversion of the functional silanes and incorporation into the branched polymer. Further studies using DSC, TGA, and cyclovoltammetry (CV) measurements have been performed. Electrochemical studies demonstrated different electrochemical properties for fcSiMe2 - and fc2SiMe-units. The CVs of polymers modified with diferrocenylsilane units exhibit the pattern of communicating ferrocenyl sites with two distinct, separate oxidation waves. The polymers were also deposited on an electrode surface and the electrodes investigated via CV, showing formation of electroactive films with promising results for the use of the materials in biosensors. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2518,2529, 2009 [source]

    Homogeneous phase polymerization of vinylidene fluoride in supercritical carbon dioxide

    Sabine Beuermann
    Abstract For the first time, stabilizer-free vinylidene fluoride (VDF) homopolymerizations were carried out in homogenous phase with supercritical CO2 using the conventional initiator di- tert butyl peroxide (DTBP). In-line FT-NIR spectroscopy showed that complete monomer conversion may be obtained. Molecular weights were determined via size-exclusion chromatography and polymer endgroup analysis by 1H-NMR spectroscopy. The number average molecular weights were below 104 g mol,1 and polydispersities ranged from 3.1 to 5.7 depending on DTBP and VDF concentration. For allowing isothermal reaction, high CO2 contents ranging from 61 to 83 wt % were used. The high-temperature and high-pressure conditions required for homogeneous polymerization did not alter the amount of defects in VDF chaining. Scanning electron microscopy indicated that regular stack-type particles are obtained upon expansion of the homogeneous polymerization mixture. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5626,5635, 2007 [source]

    Melt Spinning of Bacterial Aliphatic Polyester Using Reactive Extrusion for Improvement of Crystallization

    Roland Vogel
    Abstract This paper reports on an attempt to use reactive extrusion with peroxide as a comfortable pathway for improvement of the crystallization of poly(3-hydroxybutyrate) in a melt spinning process. At first, rheological and thermal properties of the modified melts are determined in order to assess the effect of nucleation. Then spinning tests are carried out. Molecular weights and molecular weight distributions of the spun fibers are determined by chromatographic methods. Average crystallite size is measured by wide angle X-ray scattering. Thermal and textile properties of the spun PHB fibers are also determined. An estimation of the improvement of the crystallization in the spinline and of the inhibition of the secondary crystallization in the fibers from the use of the described way of reactive extrusion is given. [source]

    Rapid Synthesis and MALDI-ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

    Maria Doycheva
    Abstract Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well-defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5,8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9,000 and 30,000,g,,mol,1. MALDI-ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths. [source]