Polymeric stationary phases for size exclusion chromatography: A review.

Synthetic and natural macromolecules are commonly used in a variety of fields such as plastics, nanomedicine, biotherapeutics, drug delivery and tissue engineering. Characterising macromolecules in terms of their structural parameters (size, molar mass and distribution, architecture) is key to have a better understanding of their structure-property relationships. Size exclusion chromatography (SEC) is a commonly used technique for polymer characterization since it offers access to the determination of the size of a macromolecule, its molar mass and the molar mass distribution. Moreover, detectors that allow the determination of true molar masses, macromolecule's architecture and the composition of copolymers can be coupled to the chromatographic system. Like other chromatographic techniques, the stationary phase is of paramount importance for efficient SEC separations. This review presents the basic principles for the design of stationary phases for SEC as well as synthetic methods currently used in the field. Current status of fully-porous polymeric stationary phases used in SEC is reviewed and their advantages and limitations are also discussed. Finally, the potential of polymer monoliths in SEC is also covered, highlighting the limitations this column technology could address. However, further development in the polymer structure is needed to consider this column technology in the field of macromolecule separation.

Two Grapes Short of a Fruit Salad: Raspberry-, Strawberry-, and Seedpod-Like Organic Microspheres via Colloidal Nanotemplating.

The morphology of surfaces critically influences their interaction with the surrounding phase. Herein, we report a modular approach for the synthesis of organic-inorganic raspberry-, strawberry-, and seedpod-like particles to template the porosity of superficially porous particles. Divinylbenzene (DVB) microspheres were employed as core particles, which were modified with polar and nonpolar polymer shells. Subsequently, silica nanoparticle templates were covalently tethered to said particles. Further grafting of polymer shells and subsequent template removal yielded superficially porous core-shell particles. In addition, we introduce a facile procedure for the synthesis of superficially porous particles without distinguishable core-shell morphology. Organic seedpod-like particles were prepared from DVB and silica templates, yielding superficially porous particles after template removal. The surface morphology of the templated particles was investigated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) was performed to prove the chemical modification of the particle surfaces.

Access to intrinsically glucoside-based microspheres with boron affinity.

Intrinsically glucoside-based microspheres are prepared in olive oil via a water in oil inverse suspension polymerization. The microspheres are characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) microscopy, and X-ray photoelectron spectroscopy (XPS), evidencing the intrinsic glucose character of the spheres. A novel boronic acid fluorescent molecule was subsequently conjugated to the microspheres in an aqueous environment, exhibiting the spatial and uniform distribution of glucoside as well as the affinity of the microspheres to bind with boron, evidenced via fluorescence spectroscopy measurements.

Online coupling of size-exclusion chromatography and IR spectroscopy to correlate molecular weight with chemical composition.

The determination of molecular weight and correlated chemical composition is of major interest for the advanced analysis of copolymers, blends, or unknown samples. In this work, we present a new way of online coupling IR spectroscopy and SEC to achieve a chemically sensitive, universally applicable SEC detector. Our method overcomes the limitations of existing spectroscopy-SEC combinations. We solved the major problems, like huge intensity of solvent signals (polymer concentration in detector <1 g L(-1) ) and short measuring time (<30 s), by recording the IR spectra with fully optimized sensitivity and by following mathematical solvent suppression. The measuring time for a certain S/N was reduced in several optimization steps by a factor of more than 70 000. The resulting sensitivity allows online coupled IR-SEC measurements.

A facile route to boronic acid functional polymeric microspheres via epoxide ring opening.

Boronic acid-functionalized microspheres are prepared for the first time via mild epoxide ring opening based on porous cross-linked polymeric microspheres (diameter ≈ 10 µm, porosity ≈ 1000 Å). Quantitative chemical analysis by XPS and EA evidences that there is a greater functionalization with boronic acid when employing a sequential synthetic method [1.7 atom% boron (XPS); 1.12 wt% nitrogen (EA)] versus a one-pot synthetic method [0.2 atom% boron (XPS); 0.60 wt% nitrogen (EA)] yielding grafting densities ranging from approximately 2.5 molecules of boronic acid per nm(2) to 1 molecule of boronic acid per nm(2), respectively. Furthermore, the boronic acid-functionalized microspheres are conjugated with a novel fluorescent glucose molecule demonstrating a homogeneous spatial distribution of boronic acid.

On-line fractionated size exclusion chromatography-nuclear magnetic resonance of polymers with ¹H and ²H nuclear magnetic resonance detection.

A new approach for on-line SEC-NMR is introduced. The method combines time slicing, fractionation with adjusted loop collection and automatic stop-flow NMR analysis. It will be called on-line fractionated SEC-NMR. This technique allows the precise determination of molar mass distributions for any polymer which can be detected by NMR. It is a significant improvement of sensitivity and accuracy compared to onflow SEC-NMR and exhibits a much easier experimental setup than off-line SEC-NMR fractionation. The new method was applied to protonated and deuterated block copolymers by using ¹H NMR and for the first time also ²H NMR detection. In this case block copolymers can be correctly characterized according to their block length distributions. As the consequence very precise molar mass parameters M(n) and M(w) can be determined. The results of the on-line fractionated SEC-NMR are in very good agreement with the multi detector analysis. The new technique also proposes a method for separating the true copolymer and low molar mass fractions in the mixture, whose structures are confirmed by HPLC-FTIR and 2D chromatography.

SEC-MR-NMR: online coupling of size exclusion chromatography and medium resolution NMR spectroscopy.

Online coupling of size exclusion chromatography together with medium resolution nuclear magnetic resonance (SEC-MR-NMR) might be one solution to the problem of chemically sensitive detection in liquid polymer chromatography. By use of a combination of SEC with a table-top, specially designed 20 MHz NMR spectrometer, based on a permanent magnet, online (1) H NMR spectra of SEC fractions can be obtained. The integration of digital filters, mechanical shims and electronic shims led to substantially improved sensitivity and chemical selectivity compared to former TD (time domain) 20 MHz instruments. (1) H NMR spectra of PMMA and PS homopolymers as well as PS-PMMA block copolymers were of sufficient quality to enable detection and de-formulation of unknown polymer compounds. (1) H NMR spectra of acceptable resolution and S/N ratio were collected online during the chromatography. The SEC separation online with the NMR measurements performed well and resulted in the proof of principle of the SEC-MR-NMR combination.

Online size exclusion chromatography-NMR for the determination of molar mass distributions of copolymers.

A general approach of size exclusion chromatography (SEC)-NMR is introduced for the determination of the classical molar mass parameters M(W), M(N), and M(P). It can be used for the determination of molar mass distributions of homopolymers and copolymers. The main advantage of SEC-NMR of copolymers is the possibility of detecting each monomer unit simultaneously with NMR as a quantitative concentration detector. Therefore, it is possible to provide the chemical compositions of copolymers at any elution volume without calibrations. In this respect, a new method will be presented for getting correct signal quantities of onflow data with sufficient NMR sensitivities. As the consequence, the chemical composition of copolymers can be correctly quantified under typical chromatographic conditions with respect to sample concentration and flow rate. Finally, the molar mass calibrations of the copolymers can be easily adjusted according to their chemical compositions. The methods were applied to polystyrene-b-poly(methyl methacrylate) block copolymers of different molar masses. The results of the molar mass distributions and the chemical composition distributions obtained by SEC-NMR are in very good agreement with the complex SEC multidetector analysis.