Separation of parent homopolymers from diblock copolymers by liquid chromatography under limiting conditions of desorption 4. Role of eluent and temperature (original) (raw)
Related papers
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. #
Macromolecules, 2000
Liquid adsorption chromatography at critical conditions (LACCC) in normal and in reversedphase modes provides independent information on the molar mass distributions of both blocks of poly-(methyl methacrylate)-block-poly(tert-butyl methacrylate), even if no information about the precursor is available. In addition, the amount of unreacted precursor can be determined, even if its molar mass is comparable to that of the total block copolymer. The reversal of elution order by changing of stationary and mobile phases makes it possible to independently characterize each block in the SEC mode of the LACCC system. Thus, complete structural information is obtained even without using two-dimensional chromatographic techniques.
Analytical Chemistry, 2014
Separation of parent homopolymers, polystyrene and poly(ethylene oxide), from the triblock copolymer polystyrene-b-poly(ethylene oxide)-b-polystyrene was investigated by means of liquid chromatography techniques. Overall suitability was evaluated and compared for size exclusion chromatography, (SEC), liquid chromatography under critical conditions of enthalpic interactions (LC CC), and liquid chromatography under limiting conditions of desorption (LC LCD). Among these techniques, LC LCD was the only one able to fully separate block copolymers from both their parent homopolymers in one single run. The efficiency of the separation was proven by 1 H NMR analysis of previously collected fractions.
Separation and Characterization of Block and Graft Copolymers by Thin-Layer Chromatography
Pure and Applied Chemistry, 1976
Feasibilities of thin-layer chromatography (TLC) and its combination with gel permeation chromatography in characterization of block and graft copolymers are discussed. The simplest application of TLC is to test the purity of block and graft samples having been subjected to purification treatment. TLC allows further to determine the compositional heterogeneity of block copolymers without interference of molecular weight, and to distinguish block samples by the difference in block sequence even on the same composition level. The latter applicability is illustrated for styrene-butadiene copolymers with different chain architecture. Finally two applications of TLC as a tool for characterization of graft systems are described: one is to isolate side-chain polymers truely grafted on mother polymer chains, and the other to isolate true graft copolymers from reaction products.
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.
Macromolecules, 2001
In the chromatographic separation of macromolecules with a porous stationary phase, the retention is determined by both size exclusion and interaction mechanisms. At the chromatographic critical condition, the effects due to the two separation mechanisms compensate each other, and the retention of homopolymer molecules becomes independent of molecular weight. Liquid chromatography at the critical condition has attracted much interest for the characterization of block copolymers since it might permit the characterization of individual blocks of a block copolymer by making one block chromatographically "invisible". In this study, we critically examine this method using two sets of styrene-isoprene block copolymers designed to have one block length constant while varying the other block length. For these block copolymer systems we found that a block cannot be made completely "invisible" at the critical condition of its homopolymer, and the retention of block copolymers is affected to some extent by the length of the "invisible" block under its chromatographic critical condition.
e-Polymers, 2005
Ethylene - methyl methacrylate block copolymers are semicrystalline polymers that dissolve in organic solvents only at high temperatures. Accordingly, microstructure analysis by solution methods must be conducted at temperatures above 130°C. For the analysis of block copolymers of different compositions several analytical techniques were used, including high-temperature size-exclusion chromatography (SEC), hyphenated SEC-FTIR, and CRYSTAF (crystallisation analysis fractionation). While SEC with refractive index detection indicated a certain multimodality of the samples, SEC coupled with FTIR revealed that the samples were chemically inhomogeneous and may contain homo- and copolymer fractions. The presence of polyethylene and poly(methyl methacrylate) homopolymers in the copolymer samples was confirmed by CRYSTAF analysis, when the total concentration as well as the carbonyl group distribution were monitored separately. Chromatographic separation of the different sample components wa...
Journal of Chromatography A, 2014
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Distributed under a Creative Commons Attribution-NonCommercial-NoDerivatives| 4.0 International License