Composition effects on ethylene/propylene copolymers studied by GPC-MALS and GPC-IR

Copolymer composition and comonomer distribution along the polymer chains are important to determine the properties and the final usefulness of the polymer. There are several ways to study directly or not directly such comonomer distribution because it has a big effect on different kind of properties. GPC-MALS (multi-angle light scattering coupled to size exclusion chromatography), GPC-IR (size exclusion chromatography with an IR detector), CRYSTAF-TREF (crystallization analysis fractionation-temperature rising elution fractionation) or NMR are very common used techniques to obtain such kind of knowledge.In this work several ethylene/propylene copolymers in the whole composition range are characterized using NMR, GPC-IR and GPC-MALS. Average copolymer composition was obtained by ¹³C-NMR and by IR, and a linear correspondence between both results was found. GPC-IR allows to study the percentage of ethylene for each M_w and to check that incorporation of ethylene is done uniformly over the entire range of molecular weights, while the incorporation of propylene presents heterogeneity in the incorporation. GPC-MALS characterization allows the q shape parameter determination and quantification of the effect that the second monomer introduces as impediment to adopt the random coil distribution.     

Molecular weight control of polyacrylamide with sodium formate as a chain‐transfer agent: Characterization via size exclusion chromatography/multi‐angle laser light scattering and determination of chain‐transfer constant

We discuss the synthesis and characterization of polyacrylamide (PAM) homopolymers with carefully controlled molecular weights (MWs). PAM was synthesized via free‐radical solution polymerization under conditions that yield highly linear polymer with minimal levels of hydrolysis. The MW of the PAM homopolymers was controlled by the addition of sodium formate (NaOOCH) to the polymerization medium as a conventional chain‐transfer agent. MWs and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi‐angle laser light scattering analysis; for polymerizations carried out to high conversion, PAM MWs ranged from 0.23 to 6.19 × 10⁶ g/mol, with most samples having PDI ≈2.0. Zero‐shear intrinsic viscosities of the polymers were determined via low‐shear viscometry in 0.514 M NaCl at 25 °C. Data derived from the polymer characterization were used to determine the chain‐transfer constant to NaOOCH under the given polymerization conditions and to calculate Mark–Houwink–Sakurada K and a values for PAM in 0.514 M NaCl at 25 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 560–568, 2003     

Molar Mass,Radius of Gyration and Second Virial Coefficient from new Static Light Scattering Equations for Dilute Solutions: Application to 21 (Macro)molecules

New equations for static light scattering of dilute binary solutions allow molar mass determination of macromolecules from measurements of scattered intensity ratios between solution and solvent (I_r). In contrast to the standard Carr–Zimm equations, they do not rely on the experimental absolute value of the Rayleigh ratio of a reference liquid. The picture shows a typical plot for the surfactant BRIJ72 in CH₂Cl₂ (M_Supplier=0.359 kg mol^?1).

     

pH‐Responsive ampholytic terpolymers of acrylamide,sodium 3‐acrylamido‐3‐methylbutanoate,and (3‐acrylamidopropyl)trimethylammonium chloride. I. Synthesis and characterization

Low-charge-density ampholytic terpolymers composed of acrylamide, sodium 3-acrylamido-3-methylbutanoate (NaAMB), and (3-acrylamidopropyl)trimethylammonium chloride were prepared via free-radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. NaOOCH was used as a chain-transfer agent during the polymerization to eliminate the effects of the monomer feed composition on the degree of polymerization (DP) and to suppress gel effects and broadening of the molecular weight distribution. The terpolymer compositions were obtained via ¹³C NMR spectroscopy, and the residual counterion content was determined via elemental analysis for Na⁺ and Cl⁻. The molecular weights (MWs) and polydispersity indices (PDIs) were determined via size exclusion chromatography/multi-angle laser light scattering (SEC–MALLS); the terpolymer MWs ranged from 1.3–1.6 × 10⁶ g/mol, corresponding to DPs of 1.6–1.9 × 10⁴ repeat units, with all terpolymers exhibiting PDIs of less than 2.0. Intrinsic viscosities determined from SEC–MALLS data and the Flory–Fox relationship were compared to intrinsic viscosities determined via low-shear dilute-solution viscometry and were found to agree rather well. Data from the SEC–MALLS analysis were used to analyze the radius of gyration/molecular weight (R_g–M) relationships and the Mark–Houwink–Sakurada intrinsic viscosity/molecular weight ([η]–M) relationships for the terpolymers. The R_g–M and [η]–M relationships revealed that most of the terpolymers exhibited little or no excluded volume effects under size exclusion chromatography conditions. Potentiometric titration of terpolymer solutions in deionized water showed that the apparent pK_a value of the poly[acrylamide-co-sodium 3-acrylamido-3-methylbutanoate-co-(3-acrylamidopropyl)trimethylammonium chloride] terpolymers increased with increasing NaAMB content in the terpolymers and increasing ratios of anionic monomer to cationic monomer at a constant terpolymer charge density. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3236–3251, 2004     

Dynamic Light Scattering Evidence for a Ligand-Induced Motion between the Two Domains of Glucoamylase G1 of Aspergillus niger with Heterobivalent Substrate Analogues

Heterobifunctional ligands that bind at the same time to the catalytic domain and to the starch-binding domain of glucoamylase induce a conformational change of the protein, as shown by dynamic light scattering. The ligands consist of acarbose and β-cyclodextrin linked together by oligoethylene glycols of variable length (see the schematic diagram).     

Study of the abnormal late co-elution phenomenon of low density polyethylene in size exclusion chromatography using high temperature size exclusion chromatography and high temperature asymmetrical flow field-flow fractionation

The elution behaviour of linear and branched polyethylene samples in SEC was studied. For the branched samples an abnormal late co-elution of large and small macromolecules manifests itself as an abnormal re-increase of the molar mass and the radius of gyration values detected with multi angle light scattering at high elution volumes in SEC. The late co-elution of small and large macromolecules cannot be explained by the SEC mechanism alone. The influence of several experimental parameters on the late co-elution was studied. It was found that the type of SEC column and the flow rate have a significant influence. The late eluting part of the sample was fractionated and separated by HT-SEC- and HT-AF4-MALS. The different results of both methods have been discussed with the aim to find possible explanations for the late elution. The experiments indicate that especially large branched structures show an increased tendency for the phenomenon.     

Reaction of oligoalcohols with diepoxides: An easy,one‐pot way to star‐shaped,multibranched polymers. II. Poly(ethylene oxide) stars—synthesis and analysis by size exclusion chromatography triple‐detection method

An Erratum has been published for this article in Journal of Polymer Science Part A: Polymer Chemistry (2004) 42(10) 2575‐2576 Starlike, highly branched (A_xB_yA_z) macromolecules having from a few to 100 arms and molar masses up to 10⁵ were prepared in three stages with the one‐pot, arms‐core‐arms method (B_y stands for y molcules of former diepoxides introduced into the core). Oligoalcohols, at least partially converted into their alcoholate counterpart states, reacted with diepoxy compounds giving star‐shaped, highly branched macromolecules. With the properly chosen conditions, complete conversion of both starting components was achieved. In this article homostars built with the first and second generation of poly(ethylene oxide) arms (A_x and A_z, respectively) are described. The number of arms (f) was determined either by direct measurements of the number‐average molcular weight (M_n) of the first and second stars (M_n of arms A_x and A_z is known) or by calculating f from branching indices g and g′ determined from the radius of gyration and the limited viscosity number measured with size exclusion chromatography (SEC) triple detection with TriSEC software. For a few samples, M_n was measured with high‐speed membrane osmometry. The progress of the stars' formation was monitored by ¹H NMR, SEC, and matrix‐assisted laser desorption/ionization time‐of‐flight methods. Functionalization of the ? OH end groups in the second generation of arms was observed by ¹H and/or ³¹P NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1576–1598, 2004     

Size exclusion chromatography with Corona charged aerosol detector for the analysis of polyethylene glycol polymer

A technique of using size exclusion chromatography (SEC) with the Corona charged aerosol detector (CAD) was developed and evaluated in comparison with refractive index (RI) and evaporative light scattering detection (ELSD) for fast screening of polyethylene glycol (PEG), a polymer used in preparing pegylated pharmaceutical compounds. These detection techniques were used in the analysis of multiple lots of PEG reagents. CAD was found to provide more accurate impurity and polydispersity profiles of PEG reagents that better differentiate their quality, while RI was not suitable for this application due to its low sensitivity and ELSD led to underestimation of the impurity and polydispersity. The accuracy of polydispersity determination by SEC-CAD was validated against a commercial reference standard of known polydispersity. The SEC-CAD technique and the observed differences between the three detectors can also be applied to polymer analysis in general.     

Viscometric,light scattering,and size‐exclusion chromatography studies on the structural changes of aqueous poly(vinyl alcohol) induced by γ‐ray irradiation

The crosslinking processes of aqueous poly(vinyl alcohol) (PVA) by γ‐ray irradiation were studied by viscometry, dynamic and static light scattering (DLS and SLS), as well as size exclusion chromatography (SEC). Increases in the intrinsic viscosity ([η]), molecular weight (M_w), hydrodynamic radius (R_h), and radius of gyration (R_g), and a decrease in second virial coefficient (A₂) were observed after γ‐ray irradiation. However, both the values of [η] and A₂ for irradiated PVA fell below the data of unirradiated PVA solutions, suggesting a conformational change of PVA chains after γ‐ray irradiation. This structural change of PVA as a result of γ‐ray irradiation was also indicated by the decreases in R_g/R_h from 1.5 to 1.39 by SLS and DLS, and in Mark–Houwink exponent α_η from 0.54 to 0.26 by SEC‐Viscometry. The broadening of the M_w distribution (MWD) as indicated by the polydispersity index increased from 2.2 to 6.5 because of γ‐ray irradiation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 214–221, 2000     

Synthesis,dynamic light scattering,and luminescence properties of copolymers containing iridium(III) bisterpyridine in the side chain

Supramolecular block‐random copolymers containing [Ir(terpy)₂]³⁺ in the side chain were synthesized via postfunctionalization of a P(S‐b‐AC_terpy) block copolymer. Absorbance and emission spectra compared to a model compound show that the polymer backbone has a minor effect on the polymer absorbance but produces a larger shift for the phosphorescence signals to higher wavelength. Dynamic light scattering of the metal complex containing copolymer studied in various solvents showed monomodal aggregation with decreasing aggregate size as the solvent dielectric constant increased. The copolymer precursor P(S‐b‐AC_terpy) shows multimodal aggregation in different solvents with the major population consisting of single chains. This difference in behavior between the two polymers is attributed to the electrolytic nature of the complex and the amphiphilicity induced by the charged metal complex. Supramolecular copolymers like these will continue to have interesting self‐organizational properties and may find applications in multicomponent systems for photoinduced charge separation processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1109–1121, 2007     

Investigation of the thermal degradation of PET, zinc phosphinate, OMPOSS and their blends—Identification of the formed species

The incorporation of both OMPOSS and Exolit OP950 (zinc phosphinate) into PET leads to increased fire retarding properties and a synergistic effect has been established between the three components. Here the thermal degradation of OMPOSS, Exolit OP950, PET and blends of them is investigated via thermal degradation in pyrolytic and thermo-oxidative conditions. All species formed during the degradation of the additives or the blends are identified by solid state NMR and X-ray diffraction in the condensed phase and by GC–MS in the gas phase. The investigation shows that no chemical interaction occurs between the additives, which suggests that the synergy responsible for the improvement of fire properties of the material has a physical origin.     

Characterisation of poly(N-isopropylacrylamide) by asymmetrical flow field-flow fractionation, dynamic light scattering, and size exclusion chromatography

Asymmetrical flow field-flow fractionation (AsFIFFF) was used to determine the hydrodynamic particle sizes, molar masses, and phase transition behaviour of various poly(N-isopropylacrylamide) (PNIPAM) samples synthesised by reversible addition--fragmentation chain transfer (RAFT) and conventional free radical polymerisation processes. The results were compared with corresponding data obtained by dynamic light scattering (DLS) and size exclusion chromatography (SEC). Agreement between the three methods was good except at higher molar masses, where the molar mass averages obtained by SEC were much lower than those obtained by AsFIFFF and light scattering. The aggregation of the polymers, which are thermally sensitive, was studied by DLS and AsFIFFF at various temperatures. In deionised water there was an abrupt change in the particle size due to phase separation at approximately equal to 32-35 degrees C. The critical temperatures determined by AsFIFFF were 3-5 degrees C higher than those obtained by DLS.     

高效液相色谱-蒸发光散射检测法测定藜芦中的介藜芦碱和藜芦胺

建立了高效液相色谱-蒸发光散射检测(HPLC-ELSD)测定藜芦中介藜芦碱、藜芦胺含量的方法,并对4种藜芦属药材样品进行了测定。采用的色谱柱为Kromasil C18柱(250 mm×4.6 mm, 5 μm),以乙腈和0.1%三氟乙酸水溶液为流动相进行梯度洗脱,洗脱程序为:0～5 min, 20%乙腈; 5～30 min, 20%乙腈～40%乙腈, 30～40 min, 40%乙腈～20%乙腈; 40～45 min, 20%乙腈;流速为0.8 mL/min;柱温为35 ℃;采用ELSD检测,漂移管温度为98 ℃,载气流速2.2 L/min 。介藜芦碱和藜芦胺的线性范围分别为42.05～980 mg/L和43.77～1020 mg/L;平均回收率分别为99.2%和101.4%,相对标准偏差分别为1.7%和2.1% (n=6);信噪比为3时,测得介藜芦碱和藜芦胺最低检测限分别为18.37 mg/kg和21.50 mg/kg。该方法快速简便、灵敏度和分离度好,适用于藜芦药材中活性生物碱的测定。     

Determination of dopamine,serotonin, and their metabolites in pediatric cerebrospinal fluid by isocratic high performance liquid chromatography coupled with electrochemical detection

A method to rapidly measure dopamine (DA), dihydroxyindolphenylacetic acid, homovanillic acid, serotonin (5‐HT) and 5‐hydroxyindoleacetic acid concentrations in cerebrospinal fluid (CSF) has not yet been reported. A rapid, sensitive, and specific HPLC method was therefore developed using electrochemical detection. CSF was mixed with an antioxidant solution prior to freezing to prevent neurotransmitter degradation. Separation of the five analytes was obtained on an ESA MD‐150 × 3.2 mm column with a flow rate of 0.37 mL/min and an acetonitrile–aqueous (5 : 95, v/v) mobile phase with 75 mM monobasic sodium phosphate buffer, 0.5 mM EDTA, 0.81 mM sodium octylsulfonate and 5% tetrahydrofuran. The optimal electrical potential settings were: guard cell +325 mV, E1 ?100 mV and E2 +300 mV. Within‐day and between‐day precisions were <10% for all analytes and accuracies ranged from 91.0 to 106.7%. DA, 5‐HT, and their metabolites were stable in CSF with antioxidant solution at 4°C for 8 h in the autoinjector. This method was used to measure neurotransmitters in CSF obtained from children enrolled on an institutional medulloblastoma treatment protocol. Copyright © 2009 John Wiley & Sons, Ltd.     

微柱高效液相色谱和质谱法测定烟草样品中的多酚

植物多酚是烟草中一类重要物质,它们在烟草中的含量对烟草质量有重要影响,因而研究烟草及其制品中的植物多酚具有重要意义。高效液相色谱法是测定其常用的一种方法。和常规高效液相色谱相比,微柱高效液相色谱由于具有流动相消耗小,分析时间短,可不分流直接和质谱连用等特点,近几年来得到了迅速发展。我们研究了用WatersXterraTMRP18(1.0×50mm,2.5μm)微柱为固定相液相色谱法测定烟草中的多酚,烟草中的主要多酚在4.0min内可达到基线分离,和常规液相色谱相比大大节约了分析时间。并用大气压电离质谱和二次质谱技术对未购到标样的绿原酸异构体作了辅助定性,方法用于烟草样品中多酚的分析,回收率在97％-103％之间,RSD在1.4％～1.9％之间,结果令人满意。     

Thermal degradation during melt processing of poly(ethylene oxide), poly(vinylidenefluoride-co-hexafluoropropylene) and their blends in the presence of additives, for conducting applications

In this paper, the thermal degradation during compounding of poly(ethylene oxide) and poly(vinylidenefluoride-co-hexafluoropropylene) and their immiscible blends was investigated. Infrared spectroscopy, size exclusion chromatography, dynamic rheology, thermogravimetric analysis, and coupled gas chromatography-mass spectroscopy were used. Most of the identified degradation products or substances are glycols, formates, lactones, ethers or even acids for long processing times. The mechanisms for the production of these chemical compounds were already reported in previous publications. Additionally, the influence of carbon black and LiV₃O₈ additives, currently used for enhancing the conductive properties, was studied. Addition of carbon black causes an increase in the PEO stability, whereas addition of LiV₃O₈ has an opposite and dramatic effect. PVDF-HFP is found to be less susceptible to degradation because of the inherent stability of fluorine-containing polymers. However, melt processing provides additional contributions to degradation because of the high viscosities.     

Determination of free fatty acids in milk and cheese procedures for extraction,clean up,and capillary gas chromatographic analysis

A rapid, reliable and precise capillary gas chromatographic method for routine quantification of short- and long-chain free fatty acids (FFA) in milk and cheese is described. Procedures of (1) lipid extraction, (2) isolation of the FFA from milk and cheese extracts, and (3) capillary gas chromatographic analysis were developed and optimized. FFA can be extracted from cheese for 95–100% with ether-heptane after grinding with sodium sulfate and addition of 2.5 M sulfuric acid. From milk, 95–100 % of the FFA (≤ C8:0) are also extracted with ether-heptane after addition of ethanol and 2.5 M sulfuric acid. Internal standards are used to compensate for the losses of lower FFA (C2:0–C8:0) in the aqueous phase. In view of the excellent recovery (98–100 %) and a considerable saving of time, the use of an aminopropyl column is preferred for the isolation of the FFA from lipid-extracts. The underivatized FFA are separated directly by capillary gas chromatography making use of columns which enable accurate and rapid (≤ 40 min) determination of FFA C2:0–C20:0. With the method described, all major FFA (C2:0–C18:3) in milk and cheese can be quantified with good repeatability (rsd less then 2 %). The method is also applicable to the analysis of short-chain fatty acids in other products.