Molar Mass (molar + mass)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Molar Mass

  • high molar mass

  • Terms modified by Molar Mass

  • molar mass distribution

  • Selected Abstracts


    Molar Mass and Structural Characteristics of Poly[(lactide- co -(aspartic acid)] Block Copolymers

    MACROMOLECULAR SYMPOSIA, Issue 1 2008
    Ida Poljan
    Abstract Summary: We report on various synthetic procedures for the preparation of biodegradable and biocompatible poly(lactide- co -aspartic acid) block copolymers based on natural monomeric units , lactic acid and aspartic acid. Multiblock poly(lactide- co -aspartic acid) copolymers of different comonomer composition were synthesized by heating a mixture of L-aspartic acid and L,L-lactide in melt without the addition of any catalyst or solvent and with further alkaline hydrolysis of the cyclic succinimide rings to aspartic acid units. Diblock poly(lactide- co -aspartic acid) copolymers with different block lengths were prepared by copolymerization of amino terminated poly(, -benzyl-L-aspartate) homopolymer and L,L-lactide with subsequent deprotection of the benzyl protected carboxyl group by hydrogenolysis. The differences in the structure, composition, molar mass characteristics, and water-solubility of the synthesized multiblock and diblock poly(lactide- co -aspartic acid) copolymers are discussed. [source]


    Characterization of New Amphiphilic Block Copolymers of N -Vinyl Pyrrolidone and Vinyl Acetate, 1 , Analysis of Copolymer Composition, End Groups, Molar Masses and Molar Mass Distributions,

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2010
    Nick Fandrich
    Abstract New amphiphilic block copolymers consisting of N -vinyl pyrrolidone and vinyl acetate were synthesized via controlled radical polymerization using a reversible addition/fragmentation chain transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) system. The synthesis was carried out in 1,4-dioxane as process solvent. In order to get conclusions on the mechanism of the polymerization the molecular structure of formed copolymers was analysed by means of different analytical techniques. 13C NMR spectroscopy was used for the determination of the monomer ratios. End groups were analysed by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This technique was also used to determine possible fragmentations of the RAFT end groups. By means of a combination of size exclusion chromatography, 13C NMR and static light scattering molar mass distributions and absolute molar masses could be analysed. The results clearly show a non-ideal RAFT mechanism. [source]


    An optimized microchip electrophoresis system for mutation detection by tandem SSCP and heteroduplex analysis for p53,gene exons,5,9

    ELECTROPHORESIS, Issue 19 2006
    Christa N. Hestekin
    Abstract With the complete sequencing of the human genome, there is a growing need for rapid, highly sensitive genetic mutation detection methods suitable for clinical implementation. DNA-based diagnostics such as single-strand conformational polymorphism (SSCP) and heteroduplex analysis (HA) are commonly used in research laboratories to screen for mutations, but the slab gel electrophoresis (SGE) format is ill-suited for routine clinical use. The translation of these assays from SGE to microfluidic chips offers significant speed, cost, and sensitivity advantages; however, numerous parameters must be optimized to provide highly sensitive mutation detection. Here we present a methodical study of system parameters including polymer matrix, wall coating, analysis temperature, and electric field strengths on the effectiveness of mutation detection by tandem SSCP/HA for DNA samples from exons,5,9 of the p53 gene. The effects of polymer matrix concentration and average molar mass were studied for linear polyacrylamide (LPA) solutions. We determined that a matrix of 8%,w/v 600,kDa LPA provides the most reliable SSCP/HA mutation detection on chips. The inclusion of a small amount of the dynamic wall-coating polymer poly- N -hydroxyethylacrylamide in the matrix substantially improves the resolution of SSCP conformers and extends the coating lifetime. We investigated electrophoresis temperatures between 17 and 35C and found that the lowest temperature accessible on our chip electrophoresis system gives the best condition for high sensitivity of the tandem SSCP/HA method, especially for the SSCP conformers. Finally, the use of electrical fields between 350 and 450,V/cm provided rapid separations (<10,min) with well-resolved DNA peaks for both SSCP and HA. [source]


    Poly(trimethylene carbonate) from Biometals-Based Initiators/Catalysts: Highly Efficient Immortal Ring-Opening Polymerization Processes

    ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009
    Marion Helou
    Abstract The ring-opening polymerization (ROP) of trimethylene carbonate (TMC) was evaluated in bulk at 60,110,C using various catalyst systems based on bio-friendly metals, including the metal bis(trimethylsilylamides) Mg[N(SiMe3)2]2, Ca[N(SiMe3)2]2(THF)2, Y[N(SiMe3)2]3, (BDI)Fe[N(SiMe3)2] [BDI=CH(CMeNC6H3 -2,6- i- Pr2)2], Fe[N(SiMe3)2]2, Fe[N(SiMe3)2]3, Zn[N(SiMe3)2]2, (BDI)Zn[N(SiMe3)2] and ZnEt2, associated with an alcohol such as isopropyl or benzyl alcohol. The actual metal alkoxide initiating species has been formed in situ prior to the addition of TMC. Introduction of the alcohol component in excess leads to the "immortal" ring-opening polymerization (ROP) of TMC. According to such an "immortal" ROP process of TMC, whichever the metal species, as many as 200 polycarbonate chains could be successfully grown from a unique metal center in a well controlled ROP process. The best performances were obtained using the discrete (BDI)Zn[N(SiMe3)2] precursor. Under optimized conditions, as many as 50,000 equivalents of TMC could be fully converted from as little as 20,ppm of this metallic precursor, allowing the preparation of a polytrimethylene carbonate (PTMC) with a molar mass as high as 185,200,g,mol,1 with a relatively narrow molar mass distribution (Mw/Mn=1.68). A double monomer feed experiment carried out with the (BDI)Zn[N(SiMe3)2]/BnOH initiating system proved the "living" character of the polymerization. Characterization of the PTMCs by NMR and size exclusion chromatography (SEC) showed well-defined ,-hydroxy-,-alkoxycarbonate telechelic polymers, highlighting the controlled character of this "living and immortal" ROP process. Using the (BDI)Zn[N(SiMe3)2] precursor, varying the alcohol (ROH) to 2-butanol, 3-buten-2-ol or 4-(trifluoromethyl)benzyl alcohol, revealed the versatility of this approach, allowing the preparation of accordingly end-functionalized HO-PTMC-OR polymers. The very low initial loading of metal catalyst considerably limits the potential toxicity and thus allows such polycarbonates to be used in the biomedical field. [source]


    Preparation and characterization of poly(dimethyldiallylammonium chloride) with high molar mass using high purity industrial monomer

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2010
    Xu Jia
    Abstract A preparation method for high molar mass poly(dimethyldiallylammonium chloride) (PDMDAAC) is reported in this article. PDMDAAC was prepared by using the high purity industrial grade dimethyldiallylammonium chloride (DMDAAC) monomer from one-step method and ammonium persulphate (APS) as the initiator. The initiator was added all at once and the reaction temperature was increased stepwise to complete the polymerization gradually. The effects of several polymerization condition variables on the intrinsic viscosity value ([,]) and monomer conversion rate (Conv.) of product PDMDAAC were investigated, respectively. The variables included: T1 (42.0 to 52.0C), T2 (47.5 to 57.5C), T3 (55.0 to 75.0C), m(DMDAAC) (60.0 to 70.0%), m(APS) : m(DMDAAC) (0.25 to 0.45%), m(Na4EDTA) : m(DMDAAC) (0 to 0.0071%). Under an optimum condition of T1 = 46.0C, T2 = 52.5C, T3 = 65.0C, m(DMDAAC) = 65.0%, m(APS) : m(DMDAAC) = 0.35%, m(Na4EDTA) : m(DMDAAC) = 0.0035%, the maximum [,] of obtained product PDMDAAC reached 3.43 dL/g, at a Conv. of 100.00%. The Mw of the product measured with GPC-MALLS was 1.034 106, polydespersity Mw/Mn was 2.421, and the Rg was 60.3 nm. The structure and properties of products were characterized by FTIR and NMR. Thermal decomposition was determined by TGA-DSC. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Influence of water content, time, and temperature on the rheological behavior of polyethylene terephtalate

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010
    A. M. C. Souza
    Abstract In this work, the main factors affecting the rheological behavior of polyethylene terephtalate (PET) in the linear viscoelastic regime (water content, time delay before test, duration of experiment, and temperature) were accessed. Small amplitude oscillatory shear tests were performed after different time delays ranging from 300 to 5000 s for samples with water contents ranging from 0.02 to 0.45 wt %. Time sweep tests were carried out for different durations to explain the changes undergone by PET before and during small amplitude oscillatory shear measurements. Immediately after the time sweep tests, the PET samples were removed from the rheometer, analyzed by differential scanning calorimetry and their molar mass was obtained by viscometry analysis. It was shown that for all the samples, the delay before test and residence time within the rheometer (i.e. duration of experiment) result in structural changes of the PET samples, such as increase or decrease of molar mass, broadening of molar mass distribution, and branching phenomena. 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


    Structural determination of ethylene-propylene-diene rubber (EPDM) containing high degree of controlled long-chain branching

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009
    Susanta Mitra
    Abstract This work highlights an attempt to characterize the degree and nature of long-chain branching (LCB) in an unknown sample of ethylene-propylene-diene rubber (EPDM). Two EPDM rubbers selected for this study were comparable in comonomer compositions but significantly different with respect to molar mass and the presence of LCB. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were used for different characterization techniques. 1H-NMR, and 13C-NMR were used for assessing the comonomer ratios and LCB. Size exclusion chromatography (SEC) equipped with triple detector system was used to determine the molar mass (both absolute and relative) and polydispersity index (PDI). Presence of branching was also detected using sec-viscometry. Rheological analysis has also been used for characterizing LCB. Finally, on the basis of the experimental findings and the available theories, an attempt was made to identify the chemical nature and degree of LCB. This study reveals the possibility of detailed characterization of molecular architecture of EPDM containing LCB by comparing with an essentially linear EPDM in light of an existing theory. 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source]


    Synthesis of Poly(3,4-ethylenedioxythiophene) latexes using poly(N -vinylpyrrolidone)-based copolymers as reactive stabilizers

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010
    Muhammad Mumtaz
    Abstract The synthesis by oxidative polymerization of well-defined poly(3,4-ethylenedioxythiophene) (PEDOT) nano-objects in the presence of modified and unmodified poly(N -vinylpyrrolidone)-based copolymers used as stabilizers in aqueous media is reported. Ammonium persulfate or a mixture of ammonium persulfate with CuCl2 or CuBr2 was used as oxidants. The effects of several parameters such as the molar mass and the concentration of the stabilizer as well as the nature of the oxidants on the size, morphology, and the conductivity of the PEDOT particles have been investigated. The distribution of the reactive moieties along the copolymer stabilizer backbone was shown to be crucial to get well-defined PEDOT nano-objects. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3841,3855, 2010 [source]


    Synthesis of thermosensitive guar-based hydrogels with tunable physico-chemical properties by click chemistry

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2010
    Morgan Tizzotti
    Abstract Thermosensitive guar-based hydrogels are obtained in water solutions by copper-catalyzed 1,3-dipolar cycloaddition between alkyne-functionalized guars and ,,,-diazido-poly[(ethylene glycol)- co -(propylene glycol)]. Characterization by TGA, HR-MAS 1H NMR, and rheology have shown that hydrogels with tunable physico-chemical properties, such as crosslinking density, viscoelasticity, swelling ratio, and so forth, could be obtained by varying the guar molar mass, the degree of alkyne functionality, the guar/crosslinker weight ratio, and the reaction temperature. Based on swelling measurements, it has been shown that the thermal sensitiveness of guar-based hydrogels is fast, reversible, and intimately related to the weight fraction of the thermosensitive crosslinker in the network. Finally, the monitoring of doxorubicin hydrochloride release has demonstrated the potential of these hydrogels as temperature-dependent drug release devices. The robust, efficient, and orthogonal approach described herein represents a general approach towards the development of well-controlled guar-based hydrogels using ,,,-diazido crosslinkers. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2733,2742, 2010 [source]


    Solving the loss of orthogonality during the polyaddition of ,-azide-,-alkyne monomers catalyzed by Cu(PPh3)3Br: Application to the synthesis of high-molar mass polytriazoles

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2010
    Sandra Binauld
    Abstract Polyaddition of an ,-azide-,-alkyne monomer by Cu(PPh3)3Br catalyzed 1,3-dipolar cycloaddition was thoroughly studied as a model system to investigate the orthogonality of this click chemistry process. Indeed, loss of chain-end functionality and occurrence of side reactions have a tremendous impact on the molar mass of polymers obtained by step growth polymerization. Particularly, SEC, 1H, and 31P NMR experiments have highlighted the occurrence of a Staudinger side-reaction between azide chain-ends and PPh3 from the copper(I) catalyst that dramatically alters Mn of the resulting polytriazoles. A significant enhancement of Mn could be achieved by using an alternative catalyst and optimized experimental conditions, that is, dilution and reaction time. 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2470,2476, 2010 [source]


    Synthesis and characterization of a series of diverse poly(2-oxazoline)s

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2009
    Kristian Kempe
    Abstract This article describes the synthesis and characterization of a variety of new poly(2-oxazoline)s. With regard to functional polymers, 2-oxazolines represent an interesting class of monomers because of the easy variation of the substituent in 2-position. Starting from the corresponding nitriles, different 2-oxazolines were obtained containing a diverse set of 2-substituents, including thioether bonds (M11), trifluoromethyl groups (M8, M10), and alkyl- or aryl groups (M1,M7). The subsequent polymerization of the majority of these monomers proceeded in a living manner, which was demonstrated by linear first-order kinetics, a linear increase of molar mass with conversion, and relatively narrow molar mass distributions. In addition, selected thermal and surface properties of the polymers were studied utilizing DSC and contact-angle measurements to determine the effects of different 2-substituents on the macroscopic properties. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3829,3838, 2009 [source]


    Synthesis and degradation of biomedical materials based on linear and star shaped polyglycidols

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2009
    Helmut Keul
    Abstract Linear and star shaped polyglycidols (synonym with polyglycerols) are prepared in a controlled ring opening polymerization of protected glycidols. Beside the molar mass and the polydispersity, the architecture of the polyglycidols is controlled by using mono- and multifunctional mono- and polydispers initiators. Copolymers of dissimilarly protected glycidols as well as copolymers with nonfunctional oxiranes were prepared by means of anionic polymerization while copolymers of protected glycidol with tetrahydrofuran were prepared by means of cationic polymerization. Polyethers with functional groups in the side chains (functional polyethers) with special emphasis on polyglycidols (containing hydroxymethyl groups in the side chains) were used to prepare multifunctional polymers and (hetero)grafted polymer brushes via chemical and enzyme catalyzed reaction. The potential of poly(glycidol- graft -,-caprolactone)- co -glycidol) prepared via enzyme catalyzed grafting of polyglycidols using ,-caprolactone as a monomer and Lipase B from Candida antarctica as a catalyst is presented. Finally, comparative degradation studies of densely and loosely grafted polyglycidols are presented and discussed. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3209,3231, 2009 [source]


    Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring-opening polymerization of glycolide

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2009
    Estelle Gautier
    Abstract Ring-opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1-dodecanol and 1,4-butanediol and tin(II) 2-ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well-defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (Tg,) of 44.8 C was thus calculated. From rheological data, the critical molar mass for entanglement, Mc, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency , = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200,230 C. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440,1449, 2009 [source]


    High molar mass ethene/1-olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008
    Erkki Aitola
    Abstract The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C1 -symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1-(7, 9)-diphenylcyclopenta-[a]-acenaphthadienyl-2-phenyl-2-cyclopentadienyl)ZrCl2 (1), ethylene(1-(7, 9)-diphenylcyclopenta-[a]-acenaphthadienyl-2-phenyl-2-fluorenyl)ZrCl2 (2), and ethylene(1-(9)-fluorenyl-(R)1-phenyl-2-(1-indenyl)ZrCl2 (3). Polyethenes produced with 1/MAO had considerable, ca. 10% amount of trans -vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1-hexene or 1-hexadecene using 1/MAO, molar mass of the copolymers varied from high to moderate (531,116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1-olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2/MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3/MAO produced polyethenes with extremely small amounts of trans -vinylene end groups and relatively low molar mass 1-hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1. These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1-olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3/MAO. 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373,382, 2008 [source]


    High-molar-mass polypropene with tunable elastic properties by hafnocene/borate catalysts

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2006
    Tanja Seraidaris
    Abstract Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, "rac"- and "meso"-dimethylsilyl(3-benzylindenyl)(2-methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self-nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep-recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743,4751, 2006 [source]


    Controlled, radical reversible addition,fragmentation chain-transfer polymerization in high-surfactant-concentration ionic miniemulsions

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 4 2004
    J. B. McLeary
    Abstract Living free-radical polymerization of methacrylate and styrenic monomers with ionic surfactants was carried out with reversible addition,fragmentation chain transfer in miniemulsion with different surfactant types and concentrations. The previously reported problem of phase separation was found to be insignificant at higher surfactant concentrations, and control of the molar mass and polydispersity index was superior to that of published miniemulsion systems. Cationic and anionic surfactants were used to examine the validity of the argument that ionic surfactants interfere with transfer agents. Ionic surfactants were suitable for miniemulsion polymerization under certain conditions. The colloidal stability of the miniemulsions was consistent with the predictions of a specific model. The living character of the polymer that comprised the latex material was shown by its transformation into block copolymers. 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 960,974, 2004 [source]


    Characterization and rheological properties of model alkali-soluble rheology modifiers synthesized by reversible addition,fragmentation chain-transfer polymerization

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2003
    E. Sprong
    Abstract Model alkali-soluble rheology modifiers of different molar masses were synthesized by the reversible addition,fragmentation chain-transfer polymerization of methyl methacrylate, methacrylic acid, and two different associative macromonomers. The polymerization kinetics showed good living character including well-controlled molar mass, molar mass linearly increasing with conversion, and the ability to chain-extend by forming an AB block copolymer. The steady-shear and dynamic properties of a core-shell emulsion, thickened with the different model alkali-soluble rheology modifiers, were measured at constant pH and temperature. The steady-shear data for latex solutions with conventional rheology modifiers exhibited the expected thickening, whereas the associative rheology modifiers showed contrasting rheology behavior. The dynamic measurements revealed that the latex solutions thickened with the conventional rheology modifiers exhibit solid-like (dominant G,) behavior as compared with the associative rheology modifiers that give the latex solution a liquid-like (dominant G,) character. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 223,235, 2003 [source]


    Nickel(II) and palladium(II) complexes with ,-dioxime ligands as catalysts for the vinyl polymerization of norbornene in combination with methylaluminoxane, tris(pentafluorophenyl)borane, or triethylaluminum cocatalyst systems,

    JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002
    Bernd Berchtold
    Abstract Nickel(II) and palladium(II) complexes with ,-dioxime ligands dimethylglyoxime, diphenylglyoxime, and 1,2-cyclohexanedionedioxime represent six new precatalysts for the polymerization of norbornene that can be activated with methylaluminoxane (MAO), the organo-Lewis acid tris(pentafluorophenyl)borane [B(C6F5)3], and triethylaluminum (TEA) AlEt3. The palladium but not the nickel precatalysts could also be activated by B(C6F5)3 alone, whereas two of the three nickel precatalysts but none of the palladium systems are somewhat active with only TEA as a cocatalyst. It was possible to achieve very high polymerization activities up to 3.2 107 gpolymer/molmetal h. With the system B(C6F5)3/AlEt3, the activation process can be formulated as the following two-step reaction: (1) B(C6F5)3 and TEA lead to an aryl/alkyl group exchange and result in the formation of Al(C6F5)nEt3,n and B(C6F5)3,nEtn; and (2) Al(C6F5)nEt3,n will then react with the precatalysts to form the active species for the polymerization of norbornene. Variation of the B:Al ratio shows that Al(C6F5)Et2 is sufficient for high activation. Gel permeation chromatography indicated that it was possible to control the molar mass of poly(norbornene)s by TEA or 1-dodecene as chain-transfer agents; the molar mass can be varied in the number-average molecular weight range from 2 103 to 9 105 g mol,1. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3604,3614, 2002 [source]


    Asymmetrical flow field-flow fractionation coupled to multiangle laser light scattering detector: Optimization of crossflow rate, carrier characteristics, and injected mass in alginate separation

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2007
    Enrica Alasonati
    Abstract The coupling of the flow field-flow fractionation (FlFFF) to differential refractive index (DRI) and multiangle laser light scattering (LS) detectors is a powerful tool for characterizing charged polysaccharides such as alginate. However, the correct interpretation of the experimental results and extrapolation of meaningful molecular parameters by using an analytical tool with such a level of complexity requires improvement of the knowledge of the alginate behavior in the channel and careful optimization of the operating conditions. Therefore, the influence of the critical operating parameters, such as crossflow rate, carrier composition and concentration, and sample load, on the alginate retention was carefully evaluated. Combined information obtained simultaneously by DRI and LS detectors over the wide range of the crossflow rate, carrier liquid concentration, and injected amount, allowed to set the appropriate combination of optimal parameters. It was found that the crossflow rate of 0.25 mL/min, carrier solution containing 510,2 mol/L ammonium or sodium chloride, and 50,100 ,g of injected sample mass were necessary to achieve complete separation and determination of the meaningful molecular characteristics. The values of the weight-average hydrodynamic radius (RHw), radius of gyration (RG), and molar mass (M), obtained under the optimal conditions were in good agreement to those found for alginates in the literature. [source]


    Hexafluoroisopropanol as size exclusion chromatography mobile phase for Polyamide 6

    JOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2004
    Raniero Mendichi
    Abstract The present study deals with the use of hexafluoroisopropanol (HFIP) as size exclusion chromatography (SEC) mobile phase for polyamide 6 (PA6). Contradictory conclusions relating to the use of HFIP as SEC mobile phase for polyamides are found in the literature. By using a multi-detector SEC apparatus equipped with on-line viscometer and multi-angle light scattering we have studied the chromatographic artifacts and the validity of the universal calibration (UC) in HFIP for different PA6 samples (hydrolytic and anionic, monofunctional or bifunctional activator). Appropriate SEC columns and optimized experimental conditions allow most of the chromatographic artifacts to be avoided, even in neat HFIP. The use of a salt in the mobile phase, namely 0.01 M tetraethylammonium nitrate (TEAN), slightly increases the elution volume for both PA6 and PMMA polymers. Under the right conditions, the UC substantially holds for PA6. The validity of the UC is not linked to the presence of TEAN in the mobile phase. With some PA6 samples, namely those anionically synthesized using a bifunctional activator, aggregation becomes a problem and the molar mass in neat HFIP is overestimated. Addition of TEAN prevents any aggregation of the above anionically synthesized PA6. In contrast, the use of a different salt, namely potassium trifluoroacetate, increases the extent of aggregation. [source]


    Effect of hindered piperidine light stabilizer molecular structure and UV-absorber addition on the oxidation of HDPE.

    JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2004
    Part 1: Long-term thermal, photo-oxidation studies
    This series of papers explores the effect of structural characteristics of 2,2,6,6-tetramethylpiperidine-based hindered amine light stabilizers (HALS) on the long-term (40 months) thermal (110C in air) and photo-stabilization (Microscal unit wavelength >300 nm) performance characteristics of high-density polyethylene formulations. Possible synergism with a triazine functional UV absorber is also explored. Under thermal degradation (measured by carbonyl index) the polymeric HALS performed best, mainly because of reduced volatilization. Additionally, >N-methyl HALS generally showed superior performance under thermal degradation. There was no synergism between an N-CH3 polymeric HALS and the UV1164 triazine additive. However, the equivalent N-H polymeric HALS interacted in a complex manner with UV1164, giving synergism and antagonism, depending on HALS/UV1164 ratio. Strong synergism was evident with the monomeric HALS when the total stabilizer level was 0.2% w/w. Reduction in the overall stabilizer level to 0.05% w/w eliminated the synergism. The UV1164 alone led to rapid and intense yellowing; however, the rate and intensity of yellowing reduced dramatically upon combination with HALS, particularly when the UV1164 level was above 0.1% w/w. When the formulation was under UV attack, the molar mass and the type of N-substitution had no influence on stabilization performance because of the relatively low temperature of testing (leading to reduced volatilization), and the similarly effective UV-stabilization routes for N-methyl HALS and N-H HALS. Under UV attack, yellowing reached a maximum and then decreased to approximately the initial level, while HALS/UV1164 combinations generally showed weak antagonism. J. Vinyl Addit. Technol. 10:79,87, 2004. 2004 Society of Plastics Engineers. [source]


    Factors influencing the adsorption of stabilizers onto carbon black: Flow microcalorimetry studies

    JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2000
    J. M. Peta
    The surface activity of various kinds of carbon black toward phenolic antioxidants and hindered amine light stabilizers (HALS) was examined by using flow microcalorimetry (FMC). Phenolic hydroxyl and ester groups were found to be the moieties responsible for the adsorption activity of primary phenolic antioxidants onto the carbon black surfaces. Furthermore, a difference in the degree of phenolic hydroxyl hindrance by alkyl groups was found to be the main factor affecting the adsorption activity of the phenol group. A difference in the degree of substitution of the piperidine amine, as well as the number and type of functionality per molecule, are important factors that were found to influence the adsorption activity of HALS. Data from adsorption studies using model compounds, some of which represented functional portions of the stabilizer molecules, reflected behavior sin ilar to that observed with the stabilizers. In addition, these latter results showed that FMC analysis can yield potentially useful information beyond that given by the usual parameters such as BET surface area, I2, DBP, and CTAB adsorption values. Differences in the behavior between types of carbon black were evident and showed that the specific surface area is not the most important factor in the adsorption/desorption activity, but also the chemical nature of the surface. From the activity observed for model compounds, it was deduced that the presence of secondary and tertiary amine in the backbone and branch structures also has an important role in the adsorption activity of polymeric HALS. In general, the observed quantities can be related to the values of adsorption/desorption energy and to the molar mass of the probe. [source]


    Systematic MALDI-TOF CID Investigation on Different Substituted mPEG 2000

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2010
    Katrin Knop
    Abstract Methoxy poly(ethylene glycol) 2000 (mPEG 2000) samples were substituted via esterification reactions to convert the hydroxyl end group of the mPEG into potential initiators for the cationic ring opening polymerization of 2-oxazolines. These substitution products were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS); in addition, detailed MALDI-TOF/TOF-collision induced dissociation (CID) MS studies were performed to introduce this method as complementary structural characterization tool allowing the detailed analysis of the prepared macromolecules. The CID of the macroinitiators revealed 1,4-hydrogen and 1,4-ethylene eliminations forming very regular fragmentation patterns which showed, depending on the end groups, different fragmentation series. Furthermore, very pronounced McLafferty,+,1 rearrangements (1,5 hydrogen-transfer) of the introduced ester end groups were observed leaving the mPEG molecule as neutral acid. This incisive loss revealed the exact molar mass for each end group and, therefore, represents an important tool for end group determination of functionalized polymers. [source]


    Synthesis of Polyurethane/Poly(1,1,2,2-tetrahydroperfluorodecyl acrylate) Particles in Supercritical Carbon Dioxide

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 5 2008
    Benjamin Renault
    Abstract A new range of end-functionalized poly(1,1,2,2-tetrahydroperfluorodecyl acrylate)s was synthesized by ATRP. Such macromonomers were used as reactive and steric stabilizers for the preparation of original core-shell polyurethane particles in supercritical carbon dioxide. The nature of the chain end functionality, as well as the molar mass of the reactive stabilizer, were varied in order to investigate the role of such parameters on the properties of the resulting materials. Due to the low surface energy of PFDA combined with the high surface roughness induced by the specific microstructure of particles deposited on a silica plate, PUR materials exhibited super-hydrophobic behavior with a water CA above 150. [source]


    Unsaturated Polyamides from Bio-Based Z -octadec-9-enedioic Acid

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 1 2008
    Francis Pardal
    Abstract A series of polyamides based on Z- octadec-9-enedioic acid, a bio-based unsaturated monomer, and aliphatic-, cycloaliphatic-, or benzylic diamines were synthesized and characterized by 1H and 13C NMR analysis, size exclusion chromatography (SEC), DSC, and dynamic-mechanical analysis (DMA). The high reaction temperature (250,C) did not lead to the degradation of diacid unit double bonds and unsaturated polyamides were obtained. The aliphatic unsaturated polyamides are semi-crystalline polymers of high molar mass, relatively flexible at room temperature. The cycloaliphatic unsaturated polyamides are semi-crystalline or amorphous, present higher melting and glass transition temperatures and are much more rigid. The aliphatic and aliphatic,aromatic unsaturated polyamides present lower Tg and Tm as compared to their parent saturated polymers. [source]


    Structure-to-Properties Relationship of Aliphatic Hyperbranched Polyesters

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007

    Abstract We investigated the effects of annealing on the rearrangement of the H-bond network microstructure and its influence on the thermal and rheological properties of the second pseudo-generation hyperbranched (HB) polyester based on 2,2-bis(methylol)propionic acid (Boltorn H20) in comparison to the fourth pseudo-generation HB polyester (Boltorn H40). During annealing the hydroxyl groups of HB polyesters form H-bonds with other hydroxyl or carbonyl groups. The formation of OH,OH H-bonds is favored at shorter annealing times, higher annealing temperatures, and for low pseudo-generation HB polyester, which has a low average molar mass, degree of branching, and core functionality. At temperatures up to 80,C, Boltorn H20 indicates faster and more extensive H-bond formation as compared to Boltorn H40. This is reflected in its larger cleavage enthalpies and higher elastic contribution to the viscoelastic response. At 90,C and above, the process of H-bond formation is delayed. Therefore, Boltorn H20 exhibits only viscous behavior in rheological measurements, and in DSC curves it shows strong exothermic transitions while heating the sample. [source]


    Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007
    Chao Zhang
    Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source]


    Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003
    Maria Bercea
    Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source]


    Hyperbranched Polyalkoxysiloxanes via AB3 -Type Monomers

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2003
    Manfred Jaumann
    Abstract We have synthesized polyethoxysiloxanes starting from the AB3 -type monomers triethoxysilanol and acetoxytriethoxysilane. The polymers are liquid and soluble in organic solvents. 29Si NMR spectroscopy and MALDI-ToF mass spectrometry analyses show that the polymers have a hyperbranched structure with additional internal cyclization. 29Si NMR spectroscopy indicates that the polymer synthesized from acetoxytriethoxysilane is less branched than the polymer synthesized from triethoxysilanol. Analysis of the molar mass and mass distribution of the polymers via size exclusion chromatography (calibrated via MALDI-ToF MS and viscosimetry) yields a molar mass of Mn,,,2 kg,,mol,1 and Mw,,,8 kg,,mol,1 for polymers synthesized from triethoxysilanol. The molar mass of the polymers synthesized from acetoxytriethoxysilane can be controlled by variation of the polymerization time in the range of Mn,,,1.8,12 kg,,mol,1 and Mw,,,2.1,2,200 kg,,mol,1. Photograph of a vial containing polyethoxysiloxane obtained from triethoxysilanol and a schematic drawing of the proposed molecular structure of the polymer. [source]


    New Polymer Syntheses, 112

    MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2003
    Hans R. Kricheldorf
    Abstract Bis(4-chlorophenyl)sebacate (BCPS) was polycondensed with 1,12-diamino-4,9-dioxadodecane or with its bistrimethylsilyl derivative in three different solvents with variation of time and temperature. The highest molecular weights were obtained in dimethylsulfoxide at 60,C. The highest fraction of cyclic polyamides was detected by MALDI-TOF mass spectrometry in the samples with the highest molecular weights. Numerous polycondensations of BCPS and 1,13-diamino-4,7,10-trioxatridecane were performed with variation of solvent, time and temperature. Again the best results were obtained in dimethylsulfoxide at 60,C. The fraction of cyclic polyamides increased with higher average molecular weights of the samples. The MALDI-TOF mass spectrum of the sample with the highest molar mass (Mn ca. 30,000 Da) exclusively displayed mass peaks of cycles (detected up to 13,000 Da). No side reactions were observed. MALDI-TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60,C/48 h (no. 3, Table 1). [source]