Use of high-performance liquid chromatography for the characterization of synthetic copolymers (original) (raw)
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Characterization of complex copolymers by two-dimensional Liquid Chromatography
Procedia Chemistry, 2010
Complex polymers were characterized by combinations of different chromatographic separation mechanisms: liquid adsorption chromatography (LAC), liquid chromatography under critical conditions (LCCC), and liquid exclusion-adsorption chromatography (LEAC). These techniques were combined off-line and on-line in two-dimensional separations. Fatty acid ethoxylates, fatty esters of polyethylene glycol (PEG) and polysorbates were analyzed by two-dimensional liquid chromatography with normal phase LAC as the first and liquid chromatography at critical conditions (LCCC) or liquid exclusion adsorption chromatography (LEAC) as the second dimension. A full separation of all oligomers to the baseline could be achieved in both dimensions. In two-dimensional separations, the offline approach is compared to comprehensive chromatography, and the scope and limitations of both techniques are discussed.
Macromolecules, 1986
The separation of styrene-methyl methacrylate copolymers by chemical composition was conducted by high-performance liquid chromatography. Stationary phases of different polarity and n-hexane/chloroform or n-hexane/tetrahydrofuran gradient elution were used. By the use of polar stationary phases such as acrylonitrile gel or silica gel, the copolymers were separated according to adsorption mechanism. The separation depended on styrene content and was essentially independent of the molecular weight of the copolymer. Nonpolar stationary phases such as styrene-divinylbenzene gel and glass beads showed separation by a phase separation mechanism reflecting both the composition and the molecular weight of the copolymer. The acrylonitrile gel provided the best performance in separation and also reproducibility in quantitative analysis. The observed chemical composition distributions agreed well with those calculated from copolymerization theory.
Separation of Ethylene−Vinyl Acetate Copolymers by High-Temperature Gradient Liquid Chromatography
Macromolecules, 2007
Ethylene-vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time-and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-temperature gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140°C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer. Full adsorption and desorption of the samples controlled by the gradient could be achieved for all compositions. Coupling of the gradient HPLC system with FTIR spectroscopy through a LC-transform interface confirmed the chemical composition separation and revealed the chemical heterogeneity of the copolymers. Conditions for liquid chromatography at critical conditions (LCCC) have been established for poly(vinyl acetate) at 140°C.
The separation of a mixture of three poly(styrene-block-t-butyl methacrylate) copolymers (PS-b-PtBMA), consisting of polystyrene (PS) blocks of similar length and t-butyl methacrylate (PtBMA) blocks of different lengths, was performed using various chromatographic techniques, that is, a gradient liquid chromatography on reversed-phase (C18 and C8) and normalphase columns, a liquid chromatography under critical conditions for polystyrene as well as a fully automated two-dimensional liquid chromatography that separates block copolymers by chemical composition in the first dimension and by molar mass in the second dimension. The results show that a partial separation of the mixture of PS-b-PtBMA copolymers can be achieved only by gradient liquid chromatography on reversed-phase columns. The coelution of the two block copolymers is ascribed to a much shorter PtBMA block length, compared to the PS block, as well as a small difference in the length of the PtBMA block in two of these copolymers, which was confirmed by SEC-MALS and NMR spectroscopy.
e-Polymers, 2005
The development of high-throughput liquid chromatographic techniques for the analysis of styrene-butyl acrylate (SBA) copolymers is discussed. The analysis time in size-exclusion chromatography (SEC) can be reduced to about 3 min per sample when high-throughput SEC columns and high flow rates are used. In gradient HPLC, small columns with improved separation efficiencies can be applied. The time requirements can be decreased to less than 2 min per sample. Using the high-throughput HPLC technique, the chemical composition distribution of high-conversion SBA copolymers can be analyzed in a fast and efficient way. The calibration of HPLC separation is conducted by coupling the HPLC system with FTIR through the LC-transform interface. A comparison of the chemical compositions of the copolymers obtained by 1 H NMR, off-line FTIR and coupled HPLC-FTIR verifies the accuracy of the high-throughput copolymer analysis approach.
Polymer, 2010
The novel separation method, liquid chromatography under limiting conditions of desorption, LC LCD enables rapid one-step discrimination of both parent homopolymers from diblock copolymers. The lowmolecular admixtures/impurities can be base-line separated, as well. The general rules for selection of the LC LCD columns are reviewed. Bare silica gel column packings are discussed in detail. Selected examples of separation are presented. They demonstrate that the principle of LC LCD separation is not affected by the particle size and initial purity of bare silica gel column packing nor by its effective pore diameter and volume. However, appropriate choice of the packing pore size facilitates base-line separation of particular sample constituents. Important may be the column history; columns saturated with previously adsorbed polymers may lose their performance. Up to a certain limit, success of the LC LCD separation does not depend on the column efficiency and reasonable results can be obtained even with the columns packed with rather big particles. This indicates possibility of the large-scale preparative applications and feasibility of the high-speed LC LCD separations.
Molecular characterization of block copolymers by means of liquid chromatography
European Polymer Journal, 2000
The full adsorption±desorption (FAD) procedure was applied to the selected model di-and tri-block copolymers. The dynamic integral desorption isotherms were measured for various homo-and block-copolymers of poly(methyl methacrylate) and poly(glycidyl methacrylate) in a system of non-porous silica±dichloroethane adsorli± tetrahydrofuran desorli. The aim was to evaluate separation selectivity of the FAD approach toward molar mass and chemical composition of macromolecules. It was demonstrated that under optimum conditions the FAD procedure can discriminate parent homopolymers from di-block copolymers, as well as di-block from tri-block copolymers when the adsorptivities of blocks dier suciently. The molar mass of both kinds of polymer chains aected the course of their desorption in present system of adsorbent±adsorli/desorli. Consequently the block copolymers studied could not be eectively fractionated according to their composition by a single FAD procedure. A combined method, full adsorption±desorption plus size exclusion chromatography was proposed for the species with selectively adsorbing blocks to provide a two dimensional fractionation of block copolymers. #