Multidetector Thermal Field-Flow Fractionation: A Unique Tool for Monitoring the Structure and Dynamics of Block Copolymer Micelles

Block copolymer micelles have attracted much attention as a versatile platform that can readily be adapted to a wide range of applications including drug delivery and the production of nanoscale patterns. However, current analytical techniques are not suitable to provide comprehensive information regarding size, molar mass, chemical composition, and micelle stability in different environments. It is shown by the analysis of polybutadiene–polystyrene micelles with various corona compositions that, in contrast to current techniques, multidetector thermal field-flow fractionation (ThFFF) is capable of separating micelles according to corona composition and providing comprehensive information on important micelle characteristics such as size, molar mass, chemical composition, and their respective distributions from a single analysis. Moreover, it is shown that ThFFF is a suitable technique to monitor the dynamics of mixed micelle formation in terms of size, molar mass, and chemical composition

Comprehensive Analysis of Oxidized Waxes by Solvent and Thermal Gradient Interaction Chromatography and Two-Dimensional Liquid Chromatography

This report addresses the comprehensive analysis of oxidized/functionalized polyethylene waxes according to chemical composition and molar mass by selective chromatographic methods. For the first time, tailored high-temperature interaction chromatography in solvent gradient (HT-SGIC) and thermal gradient (HT-TGIC) modes are used for the chemical composition separation of these materials. Separation protocols are developed using three model wax samples with different degrees of oxidation. For the chromatographic separations polar silica gel is used as the stationary phase. Solvent gradients of decane and cyclohexanone are used in HT-SGIC at 110 °C to separate the bulk waxes into several heterogeneous fractions according to polarity and the type of functionality. Column temperature and gradient manipulation are shown to influence chromatographic resolution and retention. The HT-SGIC investigations are complemented by HT-TGIC separations where a solvent mixture of decane and cyclohexanone is used as the mobile phase in isocratic mode. It is shown that HT-SGIC and HT-TGIC provide different types of separation, however, both are predominantly based on differences in functionality. To provide comprehensive information on chemical composition (functionality) and molar mass, HT-SGIC and HT-TGIC are coupled to HT-SEC, using ortho-dichlorobenzene as the second dimension mobile phase. Clear differences between oxidized and nonoxidized waxes are detected in HT-2D-LC providing comprehensive information on the molecular heterogeneity of these materials

Multidetector Thermal Field-Flow Fractionation for the Characterization of Vinyl Polymers in Binary Solvent Systems

Thermal field-flow fractionation (ThFFF) is applied to the characterization of vinyl polymers such as poly­(vinylcyclohexane) (PVCH) in terms of size, molar mass and chemical composition. It is shown by ¹H NMR that, although limited, ThFFF using single component solvents can separate polystyrene (PS) and its hydrogenated product, PVCH, according to differences in molecular microstructure. Different from single component solvents, binary solvent systems of cyclohexane and methyl ethyl ketone can provide an additional driving force (in the form of solvent partitioning) to dramatically improve the separation of PS and PVCH by ThFFF. It is found that the separation of PS and PVCH improves with increasing methyl ethyl ketone content in the mobile phase up to 30 vol %. Additionally, it is shown that the compositional distribution of PVCH in the binary solvent systems can be obtained by the online coupling of infrared spectroscopy to ThFFF

Coil−Stretch Transition of High Molar Mass Polymers in Packed-Column Hydrodynamic Chromatography

The elution behavior of high molar mass polystyrene (PS) in packed-column hydrodynamic chromatography (HDC) was studied at different eluent flow rates by using a multiangle laser light scattering (MALLS) detector. A chromatography mode transition from HDC to slalom chromatography (SC) was observed for high molar mass PS samples with abnormal elution behaviors. The critical polymer size Rg,c of the HDC to SC transition was determined by the plateau value of the Rg−Ve curve for the earliest eluting polymer fraction. The dependence of Rg,c on flow rate was explained by coil−stretch transitions of the polymer molecules in elongational flow through the packed column. The transition of chromatography mode may provide a new method to study the coil−stretch transition of polymers in elongational flow through packed beds. For high molar mass polymer samples, HDC must be performed at flow rates sufficiently low that the elongational rate in the column is less than the critical strain rate for coil−stretch transitions to occur for all species in the sample

Encapsulation of Clay by Ad-Miniemulsion Polymerization: The Influence of Clay Size and Modifier Reactivity on Latex Morphology and Physical Properties

The influence of clay platelet size and type of organic modifier (reactive or nonreactive) on highly filled hybrid latex morphology and physical properties of the resultant polymer/clay nanocomposites (PCNs) were investigated. The hybrid latexes, containing clay loadings between 30 and 50 wt % clay, were prepared using ad-miniemulsion polymerization. These materials have potential use in the packaging and coating industry since clay platelets are well-known for barrier property improvements. Comparative studies on the use of montmorillonite (MMT), a large clay platelet (average size: 50–500 nm), and Laponite (Lap), small-sized clay platelets (average size: 25–40 nm), were conducted. Two different clay modifiers were used to modify the clays, i.e., a conventional nonreactive modifier (cetyltrimethylammonium bromide (CTAB)) and a reactive modifier (vinylbenzyldodecyldimethylammonium chloride (VBDAC)). Transmission electron microscopy (TEM) imaging of the hybrid latexes clearly showed strong morphological dependency on both the type of modifier and the clay platelet size. Furthermore, TEM together with small-angle X-ray scattering (SAXS) showed that the extent of clay exfoliation was strongly dependent on the reactivity of the clay modifier, irrespective of the clay platelet size. Both the type of modifier and clay platelets size were found to have an influence on different physical properties of the resultant PCNs. The influence of clay size was clearly indicated by storage modulus and thermal stability behaviors, while that of the clay modifier was indicated by the <i>T</i>_g. Lap-based PCNs exhibited constant or increasing storage modulus and no change in thermal stability with increasing clay content, while MMT-based PCNs showed a decreasing trend in both storage modulus and thermal stability. PCNs based on clay modified with CTAB showed a decreasing <i>T</i>_g with increasing clay content, while those based on clay modified with VBDAC showed an increasing trend. It was concluded that the clay platelet size and the type of modifier play a crucial part of both the latex morphology and the physical properties of the resultant PCNs

Encapsulation of Clay by Ad-Miniemulsion Polymerization: The Influence of Clay Size and Modifier Reactivity on Latex Morphology and Physical Properties

The influence of clay platelet size and type of organic modifier (reactive or nonreactive) on highly filled hybrid latex morphology and physical properties of the resultant polymer/clay nanocomposites (PCNs) were investigated. The hybrid latexes, containing clay loadings between 30 and 50 wt % clay, were prepared using ad-miniemulsion polymerization. These materials have potential use in the packaging and coating industry since clay platelets are well-known for barrier property improvements. Comparative studies on the use of montmorillonite (MMT), a large clay platelet (average size: 50–500 nm), and Laponite (Lap), small-sized clay platelets (average size: 25–40 nm), were conducted. Two different clay modifiers were used to modify the clays, i.e., a conventional nonreactive modifier (cetyltrimethylammonium bromide (CTAB)) and a reactive modifier (vinylbenzyldodecyldimethylammonium chloride (VBDAC)). Transmission electron microscopy (TEM) imaging of the hybrid latexes clearly showed strong morphological dependency on both the type of modifier and the clay platelet size. Furthermore, TEM together with small-angle X-ray scattering (SAXS) showed that the extent of clay exfoliation was strongly dependent on the reactivity of the clay modifier, irrespective of the clay platelet size. Both the type of modifier and clay platelets size were found to have an influence on different physical properties of the resultant PCNs. The influence of clay size was clearly indicated by storage modulus and thermal stability behaviors, while that of the clay modifier was indicated by the <i>T</i>_g. Lap-based PCNs exhibited constant or increasing storage modulus and no change in thermal stability with increasing clay content, while MMT-based PCNs showed a decreasing trend in both storage modulus and thermal stability. PCNs based on clay modified with CTAB showed a decreasing <i>T</i>_g with increasing clay content, while those based on clay modified with VBDAC showed an increasing trend. It was concluded that the clay platelet size and the type of modifier play a crucial part of both the latex morphology and the physical properties of the resultant PCNs

Online HPLC–NMR: An Efficient Method for the Analysis of PMMA with Respect to Tacticity

New methods of liquid adsorption chromatography were developed to separate poly­(methyl methacrylate) (PMMA) regarding tacticity and molar mass. Gradient and isocratic chromatographic methods were applied to separate the tactic polymers. In particular, the online coupling of HPLC–NMR was used to identify and quantify the microstructural moieties during the chromatographic separation. It was possible to individually follow the elution of the syndiotactic, heterotactic as well as isotactic patterns. Several representative blends of PMMA samples of different tacticities as well as molar masses were well separated and analyzed. The quantification of all tacticities of the HPLC–NMR measurements was performed and the overall compositions were in good agreement with the data on the bulk samples. In addition, SEC–NMR data of predominantly isotactic PMMA show dependences of the tacticity on the molar mass

Online ThFFF–NMR: A Novel Tool for Molar Mass and Chemical Composition Analysis of Complex Macromolecules

For the first time, thermal field flow fractionation (ThFFF) was coupled online with ¹H NMR. ThFFF is one of the most important separation techniques for the analysis of large complex molecules and molecular assemblies. It provides information on molecular size and chemical composition in cases where multidetector setups are used. Multiple detection, however, is very complex. Using ¹H NMR as the sole detector offers a number of significant benefits. First, NMR replaces the need to use multidetector setups. Second, the structure and the microstructure of the molecules as well as the chemical composition of the molecules can be recorded. As the consequence, selective and quantitative information can be directly obtained from the NMR chromatograms. Third, the molar mass distributions of all separated species can be derived directly from these NMR chromatograms. The new online ThFFF–NMR coupling was successfully applied to homopolymers and block copolymers of different molar masses and chemical compositions

Nonlinear Ziegler–Natta-Homopolyethylene with Enhanced Crystallinity: Physical and Macromolecular Characteristics

Polyolefin engineering and design are at the forefront of a significant number of research and development laboratories, helping to bring about new and highly specific materials for tailored uses. Tailoring the chain architecture of polyolefins improves their performance and physical properties. Four unique polyethylene (PE) materials with long-chain branches (LCBPE) are studied using advanced chromatographic fractionation techniques alongside linear high-density PE (HDPE) and typical commercial low-density PE (LDPE). The absence of short-chain branching in the analyzed LCBPEs allows for a defined correlation of long-chain branching (LCB) with specific physical properties. Possible effects of side-chain crystallization on melt behavior and crystallinity clearly show that the nonlinearity in architecture positively affects crystallinity while simultaneously lowering melting temperature. The separation of polyolefins according to the LCB content is demonstrated for the first time by high-temperature interaction chromatography and thermal analysis, in addition to size exclusion chromatography coupled to differential viscometer and light scattering detectors. This study is pioneering in applying solvent gradient interaction chromatography and stationary-phase-assisted crystallization to the separation of PE regarding long-chain branching