Separation of Parent Homopolymers from Diblock Copolymers by Liquid Chromatography under Limiting Conditions of Desorption, 2 ‐ Optimization of Experimental Arrangement

Berek, Dušan

doi:10.1002/macp.200800262

Cited by 30 publications

(49 citation statements)

References 32 publications

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“…The third injection valve was situated in front of the sample injector. It was equipped with a large loop of 1.5 mL and served for the qualitative checks of sample recovery 34 by injections of neat N,N-dimethylformamide, DMF, which is a highly efficacious desorption promoting liquid, a desorli for numerous polar polymers retained within bare silica gel. Thus estimated sample recoveries in present systems were always higher than 90%.…”

Section: Measurementsmentioning

confidence: 99%

“…According to our previous studies the LC LCD sample recovery increases with the eluent strength. 34 At the same time, the barrier efficacy and/or its size/volume has to be boosted if eluent possesses very high elution strength. Otherwise the barrier may permit the break-through of the adsorbing macromolecules.…”

Section: Selections/tests Of Mobile Phasesmentioning

confidence: 99%

“…In Figure 4a the effect of time delay between injection of sample and barrier is also demonstrated. 34 Sample injected later has more time to elute in the SEC mode before its deceleration by the barrier. As a consequence, the longer time delay between barrier and sample injection, the lower is the retention volume of macromolecules, which are eventually blocked by barrier.…”

Section: Lc Lcd Measurementsmentioning

confidence: 99%

“…30,31 LC LCD was used in the separation of minor (<1%) macromolecular admixtures from the major constituents of polymer blends including parent homopolymers from the diblock copolymers. [32][33][34] The method was shown to exhibit low dependance from the eluent composition, which provides its increased experimental feasibility. Further, the sample recovery of LC LCD was very high or even complete and the narrow, focused peaks were produced.…”

mentioning

confidence: 99%

“…36,37 High selectivity of the LC LCD separations was attained when the difference was relatively large in adsorptivity of unlike polymer chains in model polymer blends and in block copolymers that contained parent homopolymers. [32][33][34] It was of interest to evaluate the LC LCD behavior of such macromolecules that exhibit only a minute difference in their adsorptivity and to attempt extension of the method applicability also to separation of polymers according to their tacticity. The selected highly stereoregular poly(methyl methacrylate)s and poly(ethyl methacrylate)s served as appropriate models.…”

mentioning

confidence: 99%

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Liquid Chromatography under Limiting Conditions of Desorption IV. Separation of Macromolecules According to Their Stereoregularity

et al. 2009

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Liquid chromatography under limiting conditions of adsorption (LC LCD) is a novel technique for separation of polymers that exhibit different extent of adsorption on the porous column packing of appropriate polarity. LC LCD is based on the selective ''barrier effect'' induced by a narrow zone of the adsorption promoting liquid that is introduced into column in front of separated macromolecules of different nature. The small molecules that form the barrier elute slowly because they permeate the packing pores. The partially or fully pore excluded polymer molecules elute rapidly. The barrier hinders fast elution of macromolecules that tend to be adsorbed within column packing; their elution is slowed down. At the same time, the non-adsorbed polymer species elute non-hindered. It is shown that due to the controlled barrier effect even a very small difference in the extent of adsorption between isotactic and syndiotactic macromolecules of poly(methacrylate)s can lead to the significant distinction in their retention volumes. While the direct LC LCD separation of poly(methyl methacrylate)s of different stereoregularity is often precluded by the aggregation of unlike macromolecules, the highly stereoregular poly(ethyl methacrylate)s of distinct kind can be easily discriminated irrespective of their molar mass. Simultaneously, the low molecular and oligomeric impurities can be removed and, if necessary they can be identified and quantified by independent methods. In this way, LC LCD can assist purification of stereoregular polymers and serve as the first step in the twodimensional liquid chromatography of their non-aggregated mixtures.

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Section: Measurementsmentioning

confidence: 99%

Section: Selections/tests Of Mobile Phasesmentioning

confidence: 99%

Section: Lc Lcd Measurementsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Liquid Chromatography under Limiting Conditions of Desorption IV. Separation of Macromolecules According to Their Stereoregularity

et al. 2009

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Size‐exclusion Chromatography Gradients

Radke

2015

Encyclopedia of Analytical Chemistry

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Gradient chromatography is an established technique for the separation of polymers according to chemical composition. Gradient separation involves injection of the dissolved polymer sample into a chromatographic column at conditions such that the sample is either adsorbed or precipitated at the column head. Afterward, the sample components are successively desorbed or redissolved and eluted from the column by changing the eluent composition in a programmed manner. However, polymers are usually soluble only in a low number of solvents. Therefore, the solvent applied for dissolving the material often prevents adsorption to the stationary phase. This results in nonretained sample components eluting with the actual injected solvent in the so‐called breakthrough peaks. Breakthrough peaks might occur as well in gradient separations based on solubility differences, when the sample solvent is strong enough to prevent the desired precipitation on the column head. These breakthrough peaks hamper method development and quantitation of the different components. Size‐exclusion chromatography (SEC) gradients provide an alternative way of performing gradient separations of high molar mass samples without the risk of breakthrough peaks. In contrast to conventional gradients in SEC gradients, the sample is dissolved in a solvent that acts as strong eluent for the sample components, allowing in principle using the commonly applied SEC solvents as starting points. This article explains the principles of SEC gradients and provides examples, showing the potential and limitations of this rather new approach.

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Separation of Polymers by Chromatography

Chang

2022

Macromolecular Engineering

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While mother nature can produce uniform macromolecules as found in many biological systems, man‐made polymers are hardly homogeneous. Synthetic polymers are usually complex mixtures of molecules differing in various molecular characteristics such as molecular weight (MW), chemical composition, functionality, microstructure, and chain architecture. For precise characterization of polymers, the multivariate distributions in all these molecular characteristics need to be measured, which is an extremely difficult task, if not impossible. In practice, however, it is often sufficient to analyze a limited number of molecular characteristics. For the purpose, liquid chromatography is the most widely used method that has made a remarkable progress during the last several decades in both instrumentation and understanding of the separation mechanism. Size exclusion chromatography (SEC) has been the most widely employed chromatographic separation technique for the characterization of synthetic polymers since its inception about a half‐century ago. Compared to traditional fractionation methods of polymers, SEC is an excellent method in precision, analysis speed, required amount of a sample, etc. Nonetheless, SEC separates the polymer molecules according to the chain size that depends on not only MW but also other molecular characteristics such as composition, chain architecture, and microstructure. Therefore, for instance, SEC cannot separate nonlinear homo‐polymers according to MW or copolymers according to the composition. In contrast to SEC in which the different pore‐accessibility of macromolecules is the main separation mechanism, interaction chromatography (IC) fractionates polymers according to the interaction strength between the polymer molecules and the sorbent. In results, IC is more sensitive to the chemical nature of the polymers than SEC. By judiciously selecting the IC separation condition, it is possible to separate polymers according to specific molecular properties with higher resolution than SEC. Furthermore, one can access to the chromatographic critical condition for a given polymer system by adjusting the solute interaction strength with the sorbent until the exclusion and interaction contributions to the solute retention are exactly compensated. At the critical condition, polymers of different MW coelute. Therefore, LC at the critical condition (LCCC) can be used as a unique tool for the characterization of polymers since one can suppress the peak dispersion by MW distribution and focus on other molecular characteristics. Recently, polymer separations using two‐dimensional LC by a rational combination of SEC, IC, or LCCC have become more and more popular for the characterization of polymers with multivariate distributions. In this article, chromatographic separation methods of synthetic polymers are reviewed with an emphasis on non‐SEC methods.

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Separation of Parent Homopolymers from Diblock Copolymers by Liquid Chromatography under Limiting Conditions of Desorption, 2 ‐ Optimization of Experimental Arrangement

Cited by 30 publications

References 32 publications

Liquid Chromatography under Limiting Conditions of Desorption IV. Separation of Macromolecules According to Their Stereoregularity

Liquid Chromatography under Limiting Conditions of Desorption IV. Separation of Macromolecules According to Their Stereoregularity

Size‐exclusion Chromatography Gradients

Separation of Polymers by Chromatography

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