Principles and potential of solvent gradient size-exclusion chromatography for polymer analysis.

The properties of a polymeric material are influenced by its underlying molecular distributions, including the molecular-weight (MWD), chemical-composition (CCD), and/or block-length (BLD) distributions. Gradient-elution liquid chromatography (LC) is commonly used to determine the CCD. Due to the limited solubility of polymers, samples are often dissolved in strong solvents.

A Method for Characterizing the Chemical Heterogeneity of Comb-Copolymers and Its Dependence on Synthesis Routes.

The heterogeneity in chemical structure of polymers is difficult to characterize and consequently remains an often-overlooked factor in mechanistic studies of functional polymers, as well as in their industrial scale optimization. In this study, we present a method to characterize chemical heterogeneity and apply it to illustrate how it can be affected differently in different synthesis routes. The polymers used are comb-copolymer dispersants used in particulate suspensions which are composed of a polycarboxylate backbone onto which PEG side chains are grafted.

The retention behavior of diblock copolymers in gradient chromatography; Similarities of diblock copolymers and homopolymers.

The retention of binary diblock copolymers in solvent gradient interaction chromatography (SGIC) was investigated theoretically and compared with experimental results. The isocratic and gradient elution behavior of binary block copolymers can be described by the equations of an equivalent homopolymer having a suitable critical eluent composition and size to pore size ratio. For diblock copolymers the adsorption-desorption transition occurs at a limiting interaction energy, which is characterized by a limiting interaction parameter c, like the critical interaction parameter of homopolymers.

Determination of molar masses of macromolecules by size exclusion chromatography-light scattering not requiring knowledge of refractive index increments.

A new approach for the calibration of SEC-light scattering (SEC-LS) setups is proposed, which requires solely the molar mass of a reference polymer. Neither the specific refractive index increment of the calibrant nor of the analyte is required. Comparison of the molar masses derived in different solvents for a large number of chemically different polymers shows that the new approach yields the same molar masses as if molar masses were derived using dn/dc to calibrate the light scattering setup.

Characterization of poly(methyl methacrylate)-graft-poly(styrene)s using various chromatographic techniques.

Two graft copolymer samples of identical average composition were synthesized by grafting living polystyrene anions onto a broadly distributed PMMA backbone. Size exclusion chromatography (SEC) with only RI-detection, SEC with viscometry and light scattering detection, SEC with UV and RI dual detection, gradient chromatography and 2-dimensional chromatography were applied to compare the information that can be obtained by the different techniques. While only limited information was retrieved by conventional SEC or SEC with molar mass sensitive detection, SEC with UV and RI revealed different chemical heterogeneity of the samples.

Consequences of on-line dialysis on polyelectrolyte molar masses determined by size-exclusion chromatography with light scattering detection.

Size-exclusion chromatography with light scattering detection experiments conducted on poly(acrylic acid) neutralized to different degrees or using hydroxides with different counterions suggest that the same counterion and degree of neutralization is observed at the detector, irrespective of salt concentration, degree of neutralization and counterion at the time of injection. This strongly supports that during the chromatographic experiment the counterions of the polyelectrolyte are exchanged with those of the eluent, resulting in an effective dialysis of the polyelectrolyte solution during the size-exclusion chromatography experiment. Consequently, the refractive index increment determined by a refractive index detector equals the refractive index increment obtained after excessive dialysis against the pure eluent.

Characterization of sodium carboxymethyl cellulose by comprehensive two-dimensional liquid chromatography.

Two series of sodium carboxymethyl celluloses (NaCMC) with average degrees of substitution (DS) ranging from 0.45 to 1.55 were synthesized from low molecular mass Avicel cellulose (Avicel samples) and from high molecular mass cotton linters (BWL samples).

Application of two-dimensional chromatography to the characterization of macromolecules and biomacromolecules.

Modern polymeric materials are heterogeneous with respect to different structural features, for instance molar mass, composition, and architecture. One-dimensional separation methods such as size-exclusion chromatography (SEC) are insufficient to fully resolve the multidimensional distributions of such complex materials. Therefore, two-dimensional separation methods are increasingly employed to characterize macromolecules.

Polymer separations by liquid interaction chromatography: principles - prospects - limitations.

Most heterogeneities of polymers with respect to different structural features cannot be resolved by only size exclusion chromatography (SEC), the most frequently applied mode of polymer chromatography. Instead, methods of interaction chromatography became increasingly important. However, despite the increasing applications the principles and potential of polymer interaction chromatography are still often unknown to a large number of polymer scientists.

Characterization of cellulose acetates according to DS and molar mass using two-dimensional chromatography.

A two-dimensional liquid chromatographic method (2D LC) was developed to analyze the heterogeneities of cellulose acetates (CA) in the DS-range DS=1.5-2.9 with respect to both, molar mass and degree of substitution (DS).

Determination of the DS distribution of non-degraded sodium carboxymethyl cellulose by gradient chromatography.

Two series of sodium carboxymethyl celluloses (NaCMCs) derived from microcrystalline cellulose (Avicel samples, DP~160) and cotton linters (BWL samples, DP~1400) with average degrees of substitution in the range DS=0.45-1.55 were analyzed by gradient liquid adsorption chromatography (gradient LAC) in order to determine their chemical composition distributions (DS distributions or 1st order heterogeneities).

Molar mass characterization of sodium carboxymethyl cellulose by SEC-MALLS.

Two series of sodium carboxymethyl celluloses (NaCMCs) derived from microcrystalline cellulose (Avicel samples) and cotton linters (BWL samples) with average degrees of substitution (DS) ranging from DS=0.45 to DS=1.55 were characterized by size exclusion chromatography with multi-angle laser light scattering detection (SEC-MALLS) in 100 mmol/L aqueous ammonium acetate (NH4OAc) as vaporizable eluent system.

Critical chromatography in ternary solvents.

The behaviour of PMMA standards in mixtures composed of two binary critical eluents was investigated. It was found that combinations of two critical eluents do not result in a molar mass independent elution (critical conditions). When mixing two binary critical eluents, elution might occur in SEC, LAC or close to critical conditions in a non-predictable fashion.

Predicting the chromatographic retention of polymers: application of the polymer model to poly(styrene/ethylacrylate)copolymers.

The retention behavior of a range of statistical poly(styrene/ethylacrylate) copolymers is investigated, in order to determine the possibility to predict retention volumes of these copolymers based on a suitable chromatographic retention model. It was found that the composition of elution in gradient chromatography of the copolymers is closely related to the eluent composition at which, in isocratic chromatography, the transition from elution in adsorption to exclusion mode occurs. For homopolymers this transition takes place at a critical eluent composition at which the molar mass dependence of elution volume vanishes.

Size exclusion chromatography-gradients, an alternative approach to polymer gradient chromatography: 2. Separation of poly(meth)acrylates using a size exclusion chromatography-solvent/non-solvent gradient.

A gradient ranging from methanol to tetrahydrofuran (THF) was applied to a series of poly(methyl methacrylate) (PMMA) standards, using the recently developed concept of SEC-gradients. Contrasting to conventional gradients the samples eluted before the solvent, i.e.

Characterization of multiblock copolymers by chromatographic techniques.

Multiblock copolymers (MBC) composed of blocks of poly(1,4-dioxanone) (PPDO) and poly(e-caprolactone) (PCL) were investigated in order to gain information on the extend of chemical heterogeneity of the samples. A gradient chromatographic method was established allowing separation of purely PPDO- from purely PCL-containing chains. Application of the gradient to MBC made of PPDO- and PCL-diols connected by trimethylhexamethylene diisocyanate (TMDI) resulted in two well separated peaks which were analyzed by means of FTIR, 1H-NMR and pyrolysis GC-MS.

Temperature gradient interaction chromatography of polymers: A molecular statistical model.

A new model describing the retention in temperature gradient interaction chromatography of polymers is developed. The model predicts that polymers might elute in temperature gradient interaction chromatography in either an increasing or decreasing order or even nearly independent of molar mass, depending on the rate of the temperature increase relative to the flow rate. This is in contrast to solvent gradient elution, where polymers elute either in order of increasing molar mass or molar mass independent.

Predicting the chromatographic retention of polymers: poly(methyl methacrylate)s and polyacryate blends.

The suitability of a retention model especially designed for polymers is investigated to describe and predict the chromatographic retention behavior of poly(methyl methacrylate)s as a function of mobile phase composition and gradient steepness. It is found that three simple yet rationally chosen chromatographic experiments suffice to extract the analyte specific model parameters necessary to calculate the retention volumes. This allows predicting accurate retention volumes based on a minimum number of initial experiments.

Comparison of retention models for polymers 1. Poly(ethylene glycol)s.

The suitability of three different retention models to predict the retention times of poly(ethylene glycol)s (PEGs) in gradient and isocratic chromatography was investigated. The models investigated were the linear (LSSM) and the quadratic solvent strength model (QSSM). In addition, a model describing the retention behaviour of polymers was extended to account for gradient elution (PM).

Simulation of size-exclusion chromatography distribution coefficients of comb-shaped molecules in spherical pores comparison of simulation and experiment.

Simulations of the distribution coefficients of linear polymers and regular combs with various spacings between the arms have been performed. The distribution coefficients were plotted as a function of the number of segments in order to compare the size exclusion chromatography (SEC)-elution behavior of combs relative to linear molecules. By comparing the simulated SEC-calibration curves it is possible to predict the elution behavior of comb-shaped polymers relative to linear ones.