Fractionation of Block Copolymers Prepared by Anionic Polymerization into Fractions Exhibiting Three Different Morphologies (original) (raw)
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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.
Rapid Communications in Mass Spectrometry, 2009
Different cationic adducts of poly(ethylene oxide)/polystyrene block co-oligomers could be produced by adjusting the salt concentration in the mobile phase using a coupling between liquid chromatography at critical conditions and electrospray ionization mass spectrometry. Formation of doubly lithiated adducts was observed at high LiCl concentration (1 mM) while lowering the salt concentration down to 0.1 mM allowed co-oligomers to be ionized with both a proton and a lithium. The fragmentation pathways observed to occur upon collision-induced dissociation of ionized copolymers were shown to be highly dependent on the nature of the cationic adducts. As a result, complementary structural information could be reached by performing MS/MS experiments on different ionic forms of the same co-oligomer molecule. On one hand, release of the nitroxide end-group as a radical from [M+2Li]2+ was followed by a complete depolymerization of the polystyrene block, allowing both this end-group and the polystyrene segment size to be determined. On the other hand, [M+H+Li]2+ precursor ions mainly dissociated via reactions involving bond cleavages within the nitroxide moiety, yielding useful structural information on this end-group. Copyright © 2009 John Wiley & Sons, Ltd.
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.
Precipitation fractionation of block copolymers
Collection of Czechoslovak Chemical Communications, 1985
Possibilities offered by classical precipitation fractionation in the preparative separation of polymer admixtures from block copolymers and in an estimate of the polydispersity in molar mass and of the heterogeneity in chemical composition of block copolymers have been examined. A mixture of a two-block copolymer, polystyrene-block-polyisoprene, with polystyrene was separated in the systems cyclohexane/l-propanol and 1,4-dioxan/l-propanol, and a mixture of three two-block styrene-isoprene copolymers having different chemical composition was fractionated in the system benzene/methanol. In the cyclohexane/l-propanol system, two commercial samples of three-block copolymers polystyrene-biock-poly(ethene-co-butene)-block--polystyrene and their mixture were fractionated. The results showed that the poiydispersity and chemical heterogeneity thus estimated are much lower than the real ones, especially due to the colloid properties of block copolymers.
Macromolecular Symposia, 2014
The analysis of PS-b-PI copolymers, synthesized by sequential living anionic polymerization was conducted by on-line hyphenation of liquid chromatography at critical conditions (LCCC) and proton nuclear magnetic resonance spectroscopy ( 1 H-NMR). Critical conditions were established for polyisoprene using 1,4-dioxane as the mobile phase and varying the column oven temperature. At these critical conditions, the polyisoprene homopolymer formed during synthesis was separated from the copolymer. The molar mass of the PS block, the chemical composition of the block copolymers as well as the microstructure of PI were determined in a single experiment.
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
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...
Macromolecular Research, 2003
A poly(ethylene oxide)-b-poly(L-lactide) diblock copolymer (PEO-b-PLLA) is characterized by matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and a block length distribution map is constructed. Although the MALDI-TOF mass spectrum of PEO-b-PLLA is very complicated, most of the polymer species were identified by isolating the overlapped isotope patterns and by fitting the overlapped peaks to the Schulz-Zimm distribution function. Reconstructed MALDI-TOF MS spectrum was nearly identical to the measured spectrum and this method shows its potential to be developed as an easy and fast analysis method of low molecular weight block copolymers.