Discrimination of block structures in liquid adsorption chromatography of polymers. Simulation and experiment.

Di- and triblocks can be separated from each other under adsorption conditions for the outer block and critical or exclusion conditions for the inner block. If the center block is uniform, even a separation according to symmetry can be achieved. This behavior is studied in much detail by theory and simulations as well as in the chromatographic experiments with block copolymers of ethylene oxide and ɛ-caprolactone.

Separation of telechelic oligomers according to architecture by liquid chromatography.

Telechelic oligomers based on diethylene glycol or lower polyethylene glycols and caprolactone or butene oxide can be separated according to their architecture by means of liquid chromatography under adsorption conditions for the hydrophobic block and critical or exclusion conditions for PEG. This behavior, which is predicted by the theory, can be verified by the experiment for block copolymers of ethylene oxide with ɛ-caprolactone and butene oxide. The individual peaks were identified by matrix-assisted time-of-flight mass spectrometry (MALDI-TOF-MS) of fractions obtained by semipreparative liquid chromatography at critical conditions of center block (PEG) and adsorption conditions for outer blocks (PCL and PBO).

Separation of polysorbates by liquid chromatography on a HILIC column and identification of peaks by MALDI-TOF MS.

Polysorbates can be separated according to their functionality and architecture by liquid chromatography on a hydrophilic interaction chromatography (HILIC) column in acetone-water mobile phases containing 90-97% acetone. The different polymer homologous series are separated according to the number of terminal hydroxy groups and elute as narrow peaks. The hydrophilic part (ethoxylates of sorbitan, isosorbide, and poly(ethyleneglycol)) and amphiphilic funtionalites (ethoxylated mono-, di-, tri-, and tetraesters) were separated by HILIC mode of high-performance liquid chromatography (HPLC).

Analysis of polyethyleneoxide macromonomers by liquid chromatography along the critical adsorption line.

Polyoxyethylene macromonomers are analyzed by one-dimensional liquid chromatography under different conditions, depending on the required information. These samples may contain polyethylene glycol (PEG) and the corresponding di(meth)acrylate besides the desired mono(meth)acrylate. The molar mass distribution (MMD) of the PEG and the monoester can be obtained by liquid adsorption chromatography (LAC) on a reversed-phase column in acetone-water with a gradient from 10% to 20% acetone.

Characterization of polyoxyethylenes according to the number of hydroxy end groups by hydrophilic interaction chromatography at critical conditions for polyethylene glycol.

Polyoxyethylenes with different functionality and architecture can be separated according to the number of terminal hydroxy groups on polar stationary phases in acetone water mobile phases containing 90-97% acetone. The best results were obtained on a HILIC column. Typical samples, which can be analyzed by this technique, are polyethylene glycols, their mono- and dialkyl ethers, macromonomers, the fatty esters of PEG, and ethoxylated glycerol.

Separation of nonionic surfactants according to functionality by hydrophilic interaction chromatography and comprehensive two-dimensional liquid chromatography.

It is shown, that amphiphilic polymers--such as polysorbates and fatty esters of polyethylene glycol can be separated by comprehensive two-dimensional liquid chromatography using a reversed phase column (under critical conditions for the polyoxyethylene chain) and a HILIC column, which may arranged in different order. The mobile phases in both dimensions can be 93-97 wt% acetone water. As the retention of higher esters on the reversed phase column is very strong, this column should be used as the first dimension.

Separation of all oligomers in polyethylene glycols and their monomethyl ethers by one-dimensional liquid chromatography.

Different polymer homologous series having the same repeat unit, but different end groups, can be separated by one-dimensional LAC according to the number of repeat units and functionality, if a favorable combination of the interaction parameters of the repeat unit and the end groups can be found. As an example, polyethylene glycol (PEG) can be determined in PEG monomethyl ethers. The molar mass distribution of the minor component in such samples can be determined even at concentrations of a few percent.

Liquid chromatography at critical conditions in ternary mobile phases: gradient elution along the critical line.

In ternary mobile phases consisting of acetone, methanol, and water, the retention of PEG on reversed-phase columns is independent on molar mass at certain compositions of the mobile phase. Along this critical adsorption line, the retention of polypropylene glycol varies quite strongly, which can be utilized in the separation of block copolymers. Gradient elution along the critical line allows a baseline separation of all oligomers in polypropylene glycol up to approximately 25 propylene oxide units.

Quantification in the analysis of polyethylene glycols and their monomethyl ethers by liquid adsorption chromatography with different detectors.

It is shown that the molar mass distribution of polyethylene glycols (PEGs) and their monomethyl ethers can be determined by liquid adsorption chromatography (LAC) on reversed phases using isocratic or gradient elution. In gradient LAC, the evaporative light scattering detector (ELSD) has to be used, which is, however, problematic with respect to quantification. The response factors of the individual oligomers depend strongly on the operating conditions, molar mass, and sample size.

Characterization of PEG in monomethyl ethers of PEG by 2-D LC.

PEGs present in samples of the corresponding monomethyl ethers are analyzed by 2-D LC with LC at critical conditions as the first and liquid adsorption chromatography as the second dimension. The fractions from the first dimension are transferred to the second one by heart-cutting using a ten-port valve. The efficiency of the separation is dramatically improved by adding water to the eluate from the first dimension before the switching valve in order to have a weaker eluent in the fraction than that of the second dimension.

Adsorption interaction parameter of polyethers in ternary mobile phases: the critical adsorption line.

It is shown that in LC of polymers, the interaction parameter in ternary mobile phases can be described by a plane, which is determined by the dependencies in binary mobile phases. Instead of a critical adsorption point, critical conditions are observed along a straight line of composition between the two critical points in binary mobile phases. Consequently, a separation of block copolymers under critical conditions for one block by an adsorption mechanism for the other block can be achieved in ternary mobile phases of different compositions, which allows an adjustment of the retention of the adsorbing block.

Retention of functional polymers in liquid adsorption chromatography: effect of the end groups in PEGs and their methyl ethers in different mobile phases.

It is shown that the end group parameter, which describes the influence of the end group on retention, can be determined in RP chromatography from two chromatograms of a nonfunctional and a monofunctional sample, if a sufficient number of peaks with the same number of repeat units in each sample can be reasonably resolved and identified. The same procedure can also be applied for pairs of di- and monofunctional polymers. End group parameters have been determined in three different mobile phases: acetonitrile-water, acetone-water and methanol-water of different compositions.

Determination of thermodynamic parameters in reversed phase chromatography for polyethylene glycols and their methyl ethers in different mobile phases.

The thermodynamic parameters (entropy and enthalpy change) and their increment per repeat unit have been determined in RP chromatography of PEG and its mono- and dimethyl ethers in different mobile phases. The different approaches for their determination and the problems related to the characteristic volumes (void volume, interstitial volume, pore volume) of the column are discussed. Very different dependences or the thermodynamic parameters were observed in aqueous mobile phases containing ACN, acetone, or methanol as organic modifier.

Characterization of polyoxyalkylene block copolymers by combination of different chromatographic techniques and MALDI-TOF-MS.

Polyoxyalkylene diblock copolymers (consisting of PEO as hydrophilic block and PBO or PHO as hydrophobic block) are characterized by combination of two dimensional liquid chromatography and MALDI-TOF-MS. Liquid chromatography under critical conditions (LCCC) is used as first dimension and fractions are collected, mobile phase evaporated and diluted in the mobile phase used in the second dimension (SEC, LCCC or LAC). This two-dimensional chromatography in combination of MALDI-TOF-MS gives information about purity of reaction products, presence of the byproducts, chemical composition and molar mass distribution of all the products.

Calibration of chromatographic systems for quantitative prediction of chromatography of homopolymers.

A method is proposed for obtaining from the experimental data the main parameters, which determine the chromatographic behavior of homopolymers: a dependence of the adsorption interaction parameter on the mobile phase composition, and the pore volume and pore size values. The interaction parameter can be determined by this method in both adsorption, critical, and SEC-type regimes of chromatography. The method is tested in 'mathematical experiments' with theoretical data that mimic experiments, and is applied to calibrate real chromatographic systems.

A data base for polymer chromatography: temperature dependence of interaction parameters in liquid adsorption chromatography.

The temperature dependence of retention behaviour of polyethylene glycol (PEG) and its mono- and dimethyl ethers was studied on various RP columns in different mobile phases. The accessible volumes and the interaction parameters were determined from slope and intercept in a plot of the elution volumes of the oligomers of a polymer homologous series as a function of the difference of the elution volumes of consecutive oligomers. A quite different dependence of the interaction parameters was observed in the different mobile phases.

Characterization of ethylene oxide-propylene oxide block copolymers by combination of different chromatographic techniques and matrix-assisted laser desorption ionization time-of-flight mass spectroscopy.

Block copolymers of ethylene oxide (EO) and propylene oxide (PO) are characterized by combination of two-dimensional chromatography and MALDI-TOF-MS. Liquid chromatography under critical conditions (LCCC) is used as first dimension and fractions are collected, mobile phase evaporated and diluted in the mobile phase used in second dimension (SEC or LAC). This two-dimensional chromatography in combination of MALDI-TOF-MS gives information about purity of reaction products, presence of the byproducts, chemical composition and molar mass distribution of all the products.

Full separation of oligomers in block copolymers of ethylene oxide and propylene oxide.

In this study di- and triblock copolymers of ethylene oxide (EO) and propylene oxide (PO) are analyzed by using CAP for one block and adsorption for the other block. This gives a complete picture of EO- and PO-based block copolymer with respect to the oligomers of both blocks. A full resolution of the individual oligomers can be achieved for both blocks up to an average molecular weight of 1000-1500 of each block.

Characterization of poly(ethylene glycol)-b-poly(epsilon-caprolactone) by two-dimensional liquid chromatography.

Block copolymers of ethylene oxide and epsilon-caprolactone were synthesized by microwave-assisted polymerization of epsilon-caprolactone with polyethylene glycol monomethyl ethers as initiator. The samples thus obtained were characterized by two-dimensional liquid chromatography with liquid chromatography at critical conditions as the first and liquid exclusion adsorption chromatography as the second dimension. A full baseline separation of all oligomers could be achieved in both dimensions.

Liquid chromatography under critical conditions: practical applications in the analysis of amphiphilic polymers.

Liquid chromatography under critical conditions (LCCC) allows the separation of block copolymers from the corresponding homopolymers as well as the separation of homopolymers according to their functionality. At the transition of exclusion and adsorption mode, the polymer chain becomes "chromatographically invisible," and thus a separation according to other structural units can be achieved. In the case of block copolymers this situation can be utilized to detect and determine unwanted homopolymers.

Amphiphilic polymers based on higher alkylene oxides Synthesis and characterization by different chromatographic techniques.

Homopolymers and block copolymers of higher epoxides (butene oxide and hexene oxide) are synthesized using 1-alkanols and polyethylene glycol monomethyl ether (PEG-MME) 1100 as initiators by anionic ring opening polymerization in bulk. Most of the samples were synthesized with controlled microwave heating in sealed vessels. Tri- and tetrablock copolymers with different repeat units in the individual blocks are synthesized by living polymerization with addition of the next monomer after complete consumption of the previous one.

Monofunctional polymers in liquid adsorption chromatography: determination of the interaction parameter in the range of weak interaction.

The main physical characteristics of monofunctionals in adsorption chromatography - the adsorption interaction parameter of the repeat units c and the interaction parameter of specific end group q - are discussed. Both parameters are independent on column dimensions and pore diameter, and depend on mobile phase composition. In a plot of elution volumes V(n) vs.

A data base for polymer chromatography: dependence of interaction parameters on mobile phase composition.

In chromatography of polymers, retention is determined by the characteristic volumes of the column (pore volume and interstitial volume), the pore diameter, and the interaction parameter. While the influence of the pore diameter is predominant in size exclusion chromatography, the key parameters in liquid adsorption chromatography are the interaction parameter and the pore surface of the column. It is shown, that the retention behaviour of polymers in liquid adsorption chromatography (LAC) can be predicted very well using the accessible volume and pore surface of the column, which can be determined very easily, and the interaction parameters from a data base.

Characterization of different reversed phase systems in liquid adsorption chromatography of polymer homologous series.

The interaction parameter of a given repeat unit in liquid adsorption chromatography (LAC) can be determined from the slope in a plot of the elution volumes versus the difference in elution volumes of subsequent monomers. In such a plot, the intercept represents the void volume, and from the slope the adsorption interaction parameter can be calculated. This parameter is independent of column dimensions and pore diameter and can thus be used as a measure of the interaction of a given repeat unit with the surface of a stationary phase in a given mobile phase composition.

The rule parameters in liquid adsorption chromatography of polymer homologous series and their determination.

The separation of polymer homologous series is governed by two rule parameters: the interaction parameter c of the repeat unit and the sorbent surface S (relation of pore volume to pore diameter). The interaction parameter is independent on column dimensions and pore diameter. In a plot of elution volumes Vn versus the difference DeltaV =Vn -Vn-1 in elution volumes of consecutive oligomers, straight lines are obtained, the intercept of which yields the accessible volume.