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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. Upon injection of the sample, such solvents may lead to broadened or poorly shaped peaks and, in unfavourable cases, to "breakthrough" phenomena, where a part of the sample travels through the column unretained. To remedy this, a technique called size-exclusion-chromatography gradients or gradient size-exclusion chromatography (gSEC) was developed in 2011. In this work, we aim to further explore the potential of gSEC for the analysis of the CCD, also in comparison with conventional gradient-elution reversed-phase LC, which in this work corresponded to gradient-elution reversed-phase liquid chromatography (RPLC). The influence of the mobile-phase composition, the pore size of the stationary-phase particles, and the column temperature were investigated. The separation of five styrene/ethyl acrylate copolymers was studied with one-dimensional RPLC and gSEC. RPLC was shown to lead to a more-accurate CCD in shorter analysis time. The separation of five styrene/methyl methacrylate copolymers was also explored using comprehensive two-dimensional (2D) LC involving gSEC, i.e. SEC × gSEC and SEC × RPLC. In 2D-LC, the use of gSEC was especially advantageous as no breakthrough could occur., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Synthetic polymers typically show dispersity in molecular weight and potentially in chemical composition. For the analysis of the chemical-composition distribution (CCD) gradient liquid chromatography may be used. The CCD obtained using this method is often convoluted with an underlying molecular-weight distribution (MWD). In this paper we demonstrate that the influence of the MWD can be reduced using very steep gradients and that such gradients are best realized utilizing recycling gradient liquid chromatography (LC↻LC). This method allows for a more-accurate determination of the CCD and the assessment of (approximate) critical conditions (if these exist), even when high-molecular-weight standards of narrow dispersity are not readily available. The performance and usefulness of the approach is demonstrated for several polystyrene standards, and for the separation of statistical copolymers consisting of styrene/methyl methacrylate and methyl methacrylate/butyl methacrylate. For the latter case, approximate critical compositions of the copolymers were calculated from the critical compositions of two homopolymers and one copolymer of known chemical composition, allowing for a determination of the CCD of unknown samples. Using this approach it is shown that the copolymers elute significantly closer to the predicted critical compositions after recycling of the gradient. This is most clear for the lowest-molecular-weight copolymer (M w  = 4.2 kDa), for which the difference between measured and predicted elution composition decreases from 7.9% without recycling to 1.4% after recycling., Competing Interests: Declaration of Competing Interest All authors declare no conflict of interest., (Copyright © 2022. Published by Elsevier B.V.)

Many materials used in a wide range of fields consist of polymers that feature great structural complexity. One particularly suitable technique for characterising these complex polymers, that often feature correlated distributions in e.g. microstructure, chemical composition, or molecular weight, is comprehensive two-dimensional liquid chromatography (LC × LC). For example, using a combination of reversed-phase LC and size-exclusion chromatography (RPLC × SEC). Efficient and sensitive LC × LC often requires focusing of the analytes between the two stages. For the analysis of large-molecule analytes, such as synthetic polymers, thermal modulation (or cold trapping) may be feasible. This approach is studied for the analysis of a styrene/butadiene "star" block copolymer. Trapping efficiency is evaluated qualitatively by monitoring the effluent of the trap with an evaporative light-scattering detector and quantitatively by determining the recovery of polystyrene standards from RPLC × SEC experiments. The recovery was dependant on the molecular weight and the temperatures of the first-dimension column and of the trap, and ranged from 46% for a molecular weight of 2.78 kDa to 86% (or up to 94.5% using an optimized set-up) for a molecular weight of 29.15 kDa, all at a first-dimension-column temperature of 80 °C and a trap temperature of 5 °C. Additionally a strategy to reduce the pressure pulse from the modulation has been developed, bringing it down from several tens of bars to only a few bar., Competing Interests: Declaration of Competing Interest All authors declare no conflicts of interests., (Copyright © 2021. Published by Elsevier B.V.)

The use of poly(styrene- co -maleic acid) (SMA) for the solubilization of lipid membranes and membrane proteins is becoming more widespread, and with this, the need increases to better understand the chemical properties of the copolymer and how these translate into membrane solubilization properties. SMA comes in many different flavors that include the ratio of styrene to maleic acid, comonomer sequence distribution, average chain length, dispersity, and potential chemical modifications. In this work, the synthesis and membrane active properties are described for 2:1 (periodic) SMA copolymers with M w varying from ∼1.4 to 6 kDa. The copolymers were obtained via an iterative RAFT-mediated radical polymerization. Characterization of these polymers showed that they represent a well-defined series in terms of chain length and overall composition ( F MAnh ∼ 0.33), but that there is heterogeneity in comonomer sequence distribution ( F MSS ∼ 0.50) and some dispersity in chain length (1.1 < Đ < 1.6), particularly for the larger copolymers. Investigation of the interaction of these polymers with phosphatidylcholine lipid self-assemblies showed that all copolymers inserted equally effectively into lipid monolayers, independent of the copolymer length. Nonetheless, smaller polymers were more effective at solubilizing lipid bilayers into nanodiscs, possibly because longer polymers are more prone to become intertwined with each other, thereby hampering their solubilization efficiency. Nanodisc sizes were independent of the copolymer length. However, nanodiscs formed with larger copolymers were found to undergo slower lipid exchange, indicating a higher stability. The results highlight the usefulness of having well-defined copolymers for systematic studies.