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Molecular Mass Distribution (molecular + mass_distribution)

Distribution by Scientific Domains
Polymers and Materials Science90%

Kinds of Molecular Mass Distribution

  • narrow molecular mass distribution
    		•

    Selected Abstracts

    Analytical characterization of PEG polymers by MEKC

    ELECTROPHORESIS, Issue 4 2010
    María R. Plata
    Abstract Characterization of PEGs with average molecular masses of up to 2000 has been achieved using MEKC with UV detection. A rapid derivatization procedure with phenyl isocyanate using microwave radiation, in order to introduce chromophore groups in PEGs, has been developed involving a reaction time of 60,s. Different optimized conditions in accordance with the molecular weight have been studied to obtain the oligomer separation. The weight-average molecular mass the number-average molecular mass and the degree of polydispersity (molecular mass distribution) were calculated for the different PEGs obtaining similar results with those certified for standards. A good precision was obtained for characterizing the different oligomers. Ethylene glycol was used as the internal standard for the analysis of low-molecular-weight PEGs. The developed method was satisfactorily applied to the characterization of these polymers in several real samples, such as lubricant eye drops, toothpaste, tap water and eye make-up remover. [source]

    Synthesis and characterization of sulfonated copolyethersulfones

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2010
    Filippo Samperi
    Abstract The present article deals with the synthesis and characterization of some sulfonated copolyethersulfones. The synthetic approach differs from the post sulfonation approach traditionally reported in the literature. The synthetic procedure is based on the use of sulfonated monomers which are then reacted with previously synthesized telechelic hydoxy-ended poly (ether sulpnone)s. Combining the MALDI-TOF MS and 1H NMR analyses, with SEC-Viscometry and TGA measurements, we demonstrate a powerful tool for characterizing the chemical composition, end chains, degree of sulfonation (DS) and molecular mass distribution (MMD) of disulfonated poly(arylene ether-sulfone) copolymers. The characterization techniques allowed to determine the exact nature of the copolymers synthesized and to reveal some interesting features about the reaction. DMA data show that the glass transition temperature of sulfonated copolymers with similar DS increase as raise their MMD. Copolymers with a DS of 10,11 mol % reach a Tg of 244,246 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3010,3023, 2010 [source]

    Influence of Short-Chain Branching of Polyethylenes on the Temperature Dependence of Rheological Properties in Shear

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 22 2007
    Florian J. Stadler
    Abstract This contribution describes the influence of short-chain branching on the temperature dependence of rheological properties of polyethylene (PE) melts in shear. The materials investigated are linear and short-chain branched, metallocene-catalyzed PEs of narrow molecular mass distribution. The linear viscoelastic properties are determined by dynamic-mechanical analysis. Short-chain branching (SCB) leads to an increase of the flow activation energy. The activation energy was found to increase linearly with rising weight comonomer content. [source]

    Kinetic Study of Ethylene Polymerization Over Supported Bis(imino)pyridine Iron (II) Catalysts

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 15 2006
    Artem A. Barabanov
    Abstract Summary: The number of active centers (CP) and propagation rate constants (kP) for polymerization of ethylene with supported catalysts LFeCl2/SiO2, LFeCl2/Al2O3 and LFeCl2/MgCl2 (L,=,2,6-(2,6-(Me)2C6H3NCMe)2C5H3N), activated by an Al(i -Bu)3 co-catalyst, were determined by a method of polymerization inhibition with radioactive 14CO. In contrast to homogeneous systems based on LFeCl2, the supported catalysts are highly active and stable in ethylene polymerization at 70,80,°C. In the presence of hydrogen, the activity of the supported catalysts substantially increases (2,4 fold). The data obtained on the effect of hydrogen on the calculated CP and kP values suggests that for ethylene polymerization without hydrogen, the "dormant" active centers are formed in the catalytic systems. A scheme for the formation of these "dormant" centers and their reactivation in presence of hydrogen is suggested. For the investigated supported catalysts the CP values were found to be only 2 to 4% of the total iron complex content in the catalysts. The kP value for the catalysts prepared using different supports (SiO2, Al2O3 and MgCl2) were close (3.2,×,104 to 4.5,×,104 L,·,(mol,·,s),1 at 70,°C). The support composition affects neither the molecular mass (MM) nor the molecular mass distribution (MMD) of the polymers produced. The obtained CP and kP values and data on the polymer MM and MMD lead to conclusion that the nature of the support has almost no effect on the structure of the active centers and the distribution of their reactivity. Effect of support on the MMD of PE produced over supported LFeCl2 catalysts. [source]

    Crystallization and chemi-crystallization of recycled photodegraded polyethylenes

    POLYMER ENGINEERING & SCIENCE, Issue 4 2005
    I.H. Craig
    Test bars (3 mm thick) made from a high-density polyethylene (HDPE), a low-density polyethylene (LDPE), and a linear low-density polyethylene (LLDPE) were injection-molded from virgin polymer and from blends containing recycled photodegraded polymer of the same kind. The molded bars were then subjected to ultraviolet (UV) exposure. Crystallinity measurements were made at different depths from the exposed surface using differential scanning calorimetry. The effects caused by processing and photodegradation were separated by comparing thermograms obtained in the initial DSC run and in a reheating run, respectively. Chemi-crystallization was produced by UV exposure. The results are interpreted in terms of molecular scission and photo-initiated molecular defects. Scission accounts for the observed chemi-crystallization, whereas the molecular defects inhibit crystallization and eventually limit chemi-crystallization. After remelting, crystallization of the photodegraded materials is influenced both by the molecular mass distribution and by the defect content of the material. The changes in crystallization behavior caused by photodegradation are different for the three polyethylenes. The results obtained using blends that included photodegraded recyclate were consistent with this material acting as a pro-degradent. The recyclability of the materials is discussed. POLYM. ENG. SCI., 45:588,595, 2005. © 2005 Society of Plastics Engineers [source]

    Large-scale extrusion processing and characterization of hybrid nylon-6/SiO2 nanocomposites

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2004
    Monserrat García
    Abstract Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide-6 (PA-6) is achieved using a twin-screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6,kg,h,1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA-6 showed higher amounts of , -phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E-modulus increased from 2.7 to 3.9,GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E, and E,) increased and tan , decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    New scope for synthesis of divinyl ether and maleic anhydride copolymer with narrow molecular mass distribution,

    POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002
    I. F. Volkova
    Abstract The alternating copolymer of divinyl ether and maleic anhydride (DIVEMA) possesses diverse biological activity and uses for production of drug delivery systems. DIVEMA's biological effects are determined by molecular mass, therefore it is necessary to have information about copolymer molecular mass and its distribution. A direct method for gel permeation chromatography analysis of DIVEMA molecular mass characteristics in aqua solution without any preliminary modification was developed. The effect of a number of factors (the concentration of monomers and their ratios, the concentration of initiator, the nature of the solvents) on DIVEMA's solution properties and molecular mass distribution was studied by gel permeation chromatography and viscometry. The approach to synthesis of DIVEMA with narrow molecular mass distribution was designed. The substantial influence of water on DIVEMA molecular mass characteristics was determined. The proposal was made that water may play a part in the formation of charge-transfer complexes playing a significant role in copolymerization. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    RAFT polymerization of styrenic-based phosphonium monomers and a new family of well-defined statistical and block polyampholytes

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2007
    Ran Wang
    Abstract We describe herein the first example of the controlled reversible addition-fragmentation chain transfer (RAFT) radical homo- and copolymerization of phosphonium-based styrenic monomers mediated with a trithiocarbonate-based RAFT chain transfer agent (CTA) directly in aqueous media. In the case of homopolymer syntheses the polymerizations proceed in a controlled fashion yielding materials with predetermined molecular characteristics as evidenced from the narrow molecular mass distributions (MMD) and the excellent agreement between the theoretical and experimentally determined molecular masses (MM). We also demonstrate the controlled nature of the homopolymerization of 4-vinylbenzoic acid with the same CTA in DMSO. We subsequently prepared both statistical and block copolymers from the phosphonium/4-vinylbenzoic acid monomers to yield the first examples of polyampholytes in which the cationic functional group is a quaternary phosphonium species. We show that the kinetic characteristics of the statistical copolymerizations are different from the homopolymerizations and proceed, generally, at a significantly faster rate although there appears to be a composition dependence on the rate. Given the inherent problems in characterizing such polyampholytic copolymers via aqueous size exclusion chromatography we have qualitatively proved their successful formation via FTIR spectroscopy. Finally, in a preliminary experiment we qualitatively demonstrate the ability of such pH-responsive block copolymers to undergo supramolecular self-assembly. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2468,2483, 2007 [source]