Multidimensional Analysis of the Complex Composition of Impact Polypropylene Copolymers: Combination of TREF, SEC-FTIR-HPer DSC, and High Temperature 2D-LC

High Performance Liquid chromatography - Fourier Transform Infrared Spectroscopy Coupling: A Comprehensive Review

This review presents a critical examination of the interface for coupling high performance liquid chromatography (HPLC) with Fourier transform infrared spectrometry (FTIR) since 2010. This coupling offers a robust analytical approach characterized by exceptional chemical specificity and the capacity to analyze complex multi-component mixtures qualitatively and quantitatively with high sensitivity, particularly in low limit of detection ranges. This coupling enables the identification of individual components of a mixture by IR after their separation by HPLC, although challenges arise from the potential distortion of infrared spectra by mobile phase components. Addressing this issue necessitates the implementation of suitable interfaces, such as flow cells or off-line indirect measurement methods like hot inert gas streams or ultrasonic nebulizers. The key parameters influencing the coupling of HPLC-FTIR include the solvent elimination methods, mode of FTIR technique, and IR background for accurate analyte identification. Moreover, the composition of the mobile phase and the utilization of buffer solutions in the HPLC mobile phase profoundly impact analyte identification by FTIR.

Unraveling the comonomer distribution in ethylene - vinyl ester terpolymers through liquid chromatography with infrared detection

Polyolefins are the most commercially relevant polymers by volume. A readily available feedstock and their tailor-made microstructure allow to adapt polyolefins to many fields of application. Important molecular design features of olefin copolymers are the molar mass distribution (MMD) with the corresponding average values, comonomer type, chemical composition distribution (CCD) with the corresponding average and the tacticity distribution (TD). Advanced separation techniques i.e., high-temperature gel permeation chromatography (HT-GPC) as well as its hyphenation with high-temperature high performance liquid chromatography (HT-HPLC) in the form of high-temperature two-dimensional liquid chromatography (HT 2D-LC) have been successfully applied in this work. This allowed to deeply analyze the molecular heterogeneities of complex polyolefin terpolymers consisting of ethylene, vinyl acetate and branched vinyl ester monomers. By using filter-based infrared detection, the capabilities of HT-GPC are further extended so that the distribution of methyl- and carbonyl groups could be obtained along the molar mass axis. Using porous graphitic carbon (PGC) as a stationary phase for HT-HPLC separation provided information about the CCD of these complex polyolefins from experimental data as part of the hyphenated approach of HT 2D-LC. The latter revealed the full MMD x CCD distribution function, which is the key for a comprehensive analysis of the bivariate molecular structure of the polyolefin terpolymers.

Probing Polyester Branching by Hybrid Trapped Ion-Mobility Spectrometry-Tandem Mass Spectrometry

Trapped ion-mobility spectrometry combined with quadrupole time-of-flight mass spectrometry (TIMS-QTOFMS) was evaluated as a tool for resolving linear and branched isomeric polyester oligomers. Solutions of polyester samples were infused directly into the ion source employing electrospray ionization (ESI). TIMS-MS provides both mobility and m/z data on the formed ions, allowing construction of extracted-ion mobilograms (EIMs). EIMs of polyester molecules showed multimodal patterns, indicating conformational differences among isomers. Subsequent TIMS-MS/MS experiments indicated mobility differences to be caused by (degree of) branching. These assignments were supported by liquid chromatography-TIMS-MS/MS analysis, confirming that direct TIMS-MS provided fast (500 ms/scan) distinction between linear and branched small oligomers. Observing larger oligomers (up to 3000 Da) using TIMS required additional molecular charging to ensure ion entrapment within the mobility window. Molecular supercharging was achieved using m-nitrobenzyl alcohol (NBA). The additional charges on the oligomer structures enhanced mobility separation of isomeric species but also added to the complexity of the obtained fragmentation mass spectra. This complexity could be partly reduced by post-TIMS analyte-decharging applying collision-induced dissociation (CID) prior to Q1 with subsequent isolation of the singly charged ions for further fragmentation. The as-obtained EIM profiles were still quite complex as larger molecules possess more possible structural isomers. Nevertheless, distinguishing between linear and symmetrically branched oligomers was possible based on measured differences in collisional cross sections (CCSs). The established TIMS-QTOFMS approach reliably allows branching information on isomeric polyester molecules up to 3000 Da to be obtained in less than 1 min analysis time.

Strengths and limitations of size exclusion chromatography for investigating single chain folding – current status and future perspectives

Synthetic approaches for Single-Chain Nanoparticles (SCNPs) developed rapidly during the last decade, opening a multitude of avenues for the design of functional macromolecular chains able to collapse into defined nanoparticles. However, the analytical evaluation of the SCNP formation process still requires critical improvements.

Multidimensional chromatographic analysis of carboxylic acid-functionalized polyethylene

Carboxy-functionalized polyethylene is comprehensively analysed using a multidimensional fractionation approach based on high-temperature HPLC, two-dimensional liquid chromatography and selective infrared detection.

Branching and molar mass analysis of low density polyethylene using the multiple preparative fractionation concept

The multiple preparative fractionation concept provides sample libraries with different degrees of branching and different molar masses that are analyzed regarding the LDPE microstructure.

Combination of preparative and two-dimensional chromatographic fractionation with thermal analysis for the branching analysis of polyethylene

Multiple preparative fractionation of LDPE provides molar mass and branching fractions that are analyzed regarding their thermal properties.

Comprehensive analysis of branched polyethylene: the multiple preparative fractionation concept

A concept for the comprehensive analysis of branched polyethylene is developed where a multiple fractionation protocol is used.

On the feasibility of determining polymer chemical heterogeneity by SEC with continuous off-line Raman detection

Examined here is the feasibility of employing Raman spectroscopy as a detection method in size-exclusion chromatography (SEC) and related macromolecular separations, for the purposes of determining the chemical heterogeneity of copolymers.

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. The present article describes in detail the advantages and experimental aspects of two-dimensional macromolecular separations. Selected examples will be discussed to explain the strategies used to separate macromolecules with respect to specific structural features.

Measuring Order in Regioregular Poly(3-hexylthiophene) with Solid-State 13C CPMAS NMR

We report on measurements of order in semicrystalline, high molar mass poly(3-hexylthiophene) (P3HT) by solid-state ¹³C cross-polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) measurements. The relative degree of crystallinity was estimated for two films with different drying conditions via X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Order determined by ¹³C NMR does not necessarily correlate with crystallinity, indicating that local order can occur in noncrystalline regions. Slow main chain dynamics influence the ¹³C NMR peak widths at lower temperatures (<0 °C), with side chain motions influencing the main chain motions. At higher temperatures (>0 °C), where narrower thiophene resonances are observed, these main chain conformation rearrangements occur on fast time scales (≪3 ms). This room-temperature dynamic disorder suggests that P3HT may be classified as a conformationally disordered (CONDIS) crystal.