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 Mw 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. 相似文献
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 (Ir). 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 (MSupplier=0.359 kg mol?1).
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). 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献
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. 相似文献