High Temperature Size Exclusion Chromatography Research Articles

Accurate Molar Mass Estimation of Polyolefin Blends Using High Temperature-size Exclusion Chromatography With Triple Detection: Insight Into Molecular Level Mixing of Polypropylene With Various Application Grades of Polyethylene.

In this study, a commercially available polypropylene homopolymer (H-PP) was blended with blow molding polyethylene (PE) grade via melt mixing using a compounding machine. The resulting blends were subjected to high-temperature size exclusion chromatography (SEC) analysis, coupled with infrared-5 (IR-5), viscometer (VISCO), and multi-angle laser light scattering (MALS) detectors. The molecular weight (MW) and MW distributions were investigated using SEC, and the exact blend compositions were evaluated using 13C nuclear magnetic resonance. The molecular-level mixing of the PP/PE blend composition was assessed by comparing the theoretical and measured weight-average MW (Mw) values obtained using different SEC detection modes. The measured average Mw values of different PP/PE blends obtained using VISCO and multi-angle light-scattering detection were found to be in close agreement with predicted blend ratios, compared to the conventional SEC technique (IR-5), with percentage errors ranging from -4.53 to -5.99 and 1.57 to 7.65, respectively. The linear relationship between the melt flow rate (MFR) and Mw was studied to assess the molecular-level mixing behavior of the prepared blends using different SEC detection modes. Furthermore, the SEC methodology was extended to other application grades of PE with varying MFRs to verify the blend mixing behavior with H-PP, and the obtained results are discussed.

Bacterial Degradation of Low-Density Polyethylene Preferentially Targets the Amorphous Regions of the Polymer.

Low-density polyethylene (LDPE) is among the most abundant synthetic plastics in the world, contributing significantly to the plastic waste accumulation problem. A variety of microorganisms, such as Cupriavidus necator H16, Pseudomonas putida LS46, and Pseudomonas chlororaphis PA2361, can form biofilms on the surface of LDPE polymers and cause damage to the exterior structure. However, the damage is not extensive and complete degradation has not been achieved. The changes in polymer structure were analyzed using Time-domain Nuclear Magnetic Resonance (TD-NMR), High-Temperature Size-Exclusion Chromatography (HT-SEC), Differential Scanning Calorimetry (DSC), and Gas Chromatography with a Flame Ionization Detector (GC-FID). Limited degradation of the LDPE powder was seen in the first 30 days of incubation with the bacteria. Degradation can be seen in the LDPE weight loss percentage, LDPE degradation products in the supernatant, and the decrease in the percentage of amorphous regions (from >47% to 40%). The changes in weight-average molar mass (Mw), number-average molar mass (Mn), and the dispersity ratio (Đ) indicate that the low-molar mass fractions of the LDPE were preferentially degraded. The results here confirmed that LDPE degradation is heavily dependent on the presence of amorphous content and that only the amorphous content was degraded via bacterial enzymatic action.

Investigation on the Durability of a Polypropylene Geotextile under Artificial Aging Scenarios

Geosynthetics are widely used in various civil engineering applications, such as geotextiles in coastal protection, and display a sustainable alternative to natural mineral materials. However, the full benefits of using geosynthetics can only be gained with a long service lifetime of the products. With the use of added stabilizers to the polymers, service lifetimes can be achieved in the range of 100 years. Therefore, accelerated aging methods are needed for the assessment of the long-term performance of geotextiles. In the present study, the behavior of geosynthetic materials made of polypropylene was investigated under artificial aging conditions involving elevated temperatures ranging from 30 to 80 °C, increased oxygen pressures ranging from 10 to 50 bar in water-filled autoclaves, and UV irradiation under atmospheric conditions. ATR-IR spectroscopy was employed to detect the increase in the carbonyl index over various aging durations, indicating the oxidative degradation of the geotextile. The most pronounced increase was observed in the case of aging through UV irradiation, followed by thermal aging. Elevated pressure, on the other hand, had a lower impact on oxidation. High-temperature size exclusion chromatography was utilized to follow the reduction in molar mass under different degradation conditions, and the results were consistent with those obtained from ATR-IR spectroscopy. In polyolefins such as polypropylene, Hindered Amine Stabilizers (HAS) are used to suppress oxidation caused by UV radiation. The quantitative analysis of HAS was carried out using a UV/Vis method and HPLC. The degradation of UV stabilizers during the aging of geotextiles is responsible for the oxidation and the reduction in the molar mass of polypropylene. From the results, it can be concluded that applications of PP geotextile without soil or sand cover might cause the risk of the formation of microplastic particles. Material selection, design, and maintenance of the construction must follow best practices, including the system’s removal or replacement at end-of-life. Otherwise, a sustainable use of geotextiles in civil engineering is not possible.

Branched Comonomers in LLDPE—Influence of Short Chain Branch Shape on Crystallinity

AbstractThe crystallinity of Linear Low‐Density Polyethylene (LLDPE) is influenced significantly by short‐chain branches (SCBs) present in the backbone of the polymer. Despite the importance of this aspect, with only a few linear comonomers being currently used in the commercial production of LLDPE. It is found that by introducing branched comonomers, the melting point and crystallinity of LLDPE can be influenced to a greater extent than with linear comonomers. Since only a few linear comonomers are currently used in the production of LLDPE, the characterization of LLDPEs with branched comonomer has been often overlooked. By combining High‐Temperature‐Size‐Exclusion Chromatography (HT‐SEC), Nuclear Magnetic Resonance (NMR) spectroscopy, and Infrared (IR) spectroscopy, it is shown that standard HT‐SEC analysis using an IR detector is also applicable to polymers containing branched comonomers.

Effects of Thermal Aging on Molar Mass of Ultra-High Molar Mass Polyethylene Fibers.

Ultra-high molar mass polyethylene (UHMMPE) is commonly used for ballistic-resistant body armor applications due to the superior strength of the fibers fabricated from this material combined with its low density. However, polymeric materials are susceptible to thermally induced degradation during storage and use, which can reduce the high strength of these fibers, and, thus, negatively impact their ballistic resistance. The objective of this work is to advance the field of lightweight and soft UHMMPE inserts used in various types of ballistic resistant-body armor via elucidating the mechanisms of chemical degradation and evaluating this chemical degradation, as well as the corresponding physical changes, of the UHMMPE fibers upon thermal aging. This is the first comprehensive study on thermally aged UHMMPE fibers that measures their decrease in the average molar mass via high-temperature size exclusion chromatography (HT-SEC) analysis. The decrease in the molar mass was further supported by the presence of carbon-centered free radicals in the polyethylene that was detected using electron paramagnetic resonance (EPR) spectroscopy. These carbon-centered radicals result from a cascade of thermo-oxidative reactions that ultimately induce C–C ruptures along the backbone of the polymer. Changes in the crystalline morphology of the UHMMPE fibers were also observed through wide-angle X-ray diffraction (WAXS), showing an increase in the amorphous regions, which promotes oxygen diffusion into the material, specifically through these areas. This increase in the amorphous fraction of the highly oriented polyethylene fibers has a synergistic effect with the thermo-oxidative degradation processes and contributes significantly to the decrease in their molar mass.

Characterization of ethylene-propylene-diene terpolymers using high-temperature size exclusion chromatography coupled with an ultraviolet detector

The distribution of the pendant double bond along the molar mass axis impacts the vulcanization behavior of ethylene-propylene-diene (EPDM) terpolymers. Yet, the analysis of this parameter has so far been hampered by the lack of suitable detection methods. Towards this goal we have investigated the potential of ultraviolet detector (UV) detection for high temperature size exclusion chromatography of EPDM terpolymers containing 5-ethylidene-2-norbornene (ENB), dicyclopentadiene (DCPD), and vinyl norbornene (VNB) as termonomer. The influence of termonomer structure and experimental parameters such as, mobile phase, analyte concentration and temperature on the spectroscopic response was probed. EPDM containing ENB showed a significantly stronger UV-absorption compared to terpolymers with VNB and DCPD. The absorbance was found to correlate with the sample concentration approaching signal saturation at higher ENB content. Generally, temperature did not have any significant effect on the UV absorbance of EPDM. Based on the results, a method was developed, which can profile the content of ENB along the molar mass axis. An evaporative light scattering detector (ELSD) was employed to monitor the analyte concentration, in combination with the UV detector, to quantitatively measure the distribution of ENB content along the molar mass distribution. This work could be feasible for the other two commercial relevant termonomers DCPD and VNB.

Impact of Polymerization Process Parameters on Improved Comonomer Incorporation Behavior in Ziegler‐Natta Catalysis

AbstractZiegler‐Natta (ZN) based co‐polymerization processes for the production of linear low‐density polyethylene (LLDPE) generally give rise to a non‐uniform incorporation distribution of the comonomer. It has been shown that lowering the titanation temperature during catalyst synthesis can increase the evenness of this distribution. However, polymerization process parameters also affect the resulting incorporation distribution. To investigate these factors, a ZN system using a variety of comonomer‐types, at various ‐concentrations and polymerization temperatures is studied. The molecular properties of the polymer samples obtained are analyzed by high‐temperature size‐exclusion chromatography (HT‐SEC). It is shown that a more uniform incorporation distribution of the comonomer can be achieved by lowering either the polymerization temperature or the comonomer concentration, and that lowering both increases the effect.

Effect of viscoelasticity on the foaming behaviour of long-chain branched polypropylene with different branching degrees analysed by using bubble-growth modelling

Long-chain branched polypropylene (LCB-PP) was generated by a melt grafting reaction with trimethylolpropane triacrylate (TMPTA) as the grafting monomer and zinc dimethyldithiocarbamate (ZDMC) or styrene (St) as the co-monomers. High-temperature size exclusion chromatography (HT-SEC) was used to characterize the molecular mass, molecular mass distribution and branching degree of the modified PP. Subsequently, linear and nonlinear viscoelasticity data were obtained by a small amplitude oscillatory shear (SAOS) test and uniaxial extensional viscosity measurement. The pressure balanced bubble-growth (PBB) model was used to calculate the critical coalescence radius (CCR) curves for PP to quantitatively correlate the viscoelasticity and foamability and evaluate the foamability of PP combined with batch foaming. It is shown that with increasing branching degree, the foam shows a better resistance to bubble coalescence, resulting in a more regular bubble structure and a higher expansion ratio. Moreover, viscosity should be controlled over an appropriate range for realising good foamability; otherwise, excessive viscosity can suppress bubble growth and limit the expansion ratio. MPPZ4 modified with 4 wt% TMPTA and 0.4 wt% ZDMC showed the best foamability. A combination of the PBB model and batch foaming experiment is used to quantitatively explain the contribution of LCB to foaming.

Fractionation of chain walking polyethylene and elucidation of branching, conformation and molar mass distributions

State-of-the-art liquid interaction chromatography (IC) allows separation of macromolecules according to chemical composition (CC), functionality or molecular topology in contrast to size-based approaches such as size exclusion chromatography (SEC), which has its limitations in distinguishing chemical structures. Yet, for macromolecules with multivariate molecular distributions, online identification and characterization of distinct components in bulk samples is a considerable challenge. A useful approach to narrow down the complexity of a given sample is preparative molar mass fractionation (pMMF) that provides fractions in mg or g scale, which can be subjected to further advanced analysis to elucidate the physical and structural properties of the sample. In this study, novel chain-walking polyethylenes (CWPE), which differ substantially in macromolecular architecture, are fractionated using pMMF. Using IC in temperature and solvent gradient modes (TGIC, SGIC), the pMMF fractions are separated according to branching topology. Quadruple-detector high temperature SEC is carried out to determine the physical properties and study the MM-dependent structural transformation of CWPE. A detailed branching analysis was carried out by means of nuclear magnetic resonance. Two-dimensional liquid chromatography (LC) hyphenating IC and SEC provides comprehensive bivariate correlations between MM and molecular topology.

A comprehensive investigation into the structure-property relationship of wax and how it influences the properties of hot melt adhesives

A detailed study was conducted on seven different waxes used in hot melt adhesive formulations together with conventional resins and tackifiers, to characterize the waxes and investigate the effects of wax structure and morphology on the thermal behaviour and basic properties of the resultant hot melt adhesive formulations (HMAs). The waxes selected included representatives of each of the following types: Fischer-Tropsch wax (FT), fully refined paraffin wax (FRP), by-product polyethylene wax (BPPE), microcrystalline wax (microwax), alpha-olefin wax (AO), carnauba wax and first intention polyethylene wax (FIPE). Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), high temperature size exclusion chromatography (HT-SEC), nuclear magnetic resonance spectroscopy (NMR) and confocal laser scanning microscopy (CLSM) were used as analytical tools to characterize the waxes. Molecular chain architecture as determined by solution 13C NMR highlighted the superior chain linearity of FT wax. Methyl, ethyl and butyl short chain branching were detected in other waxes. Solid-state 13C CP-MAS NMR provided information on the semi-crystalline nature of the waxes. FIPE, AO and Microwax showed significant structural mobility at room temperature as observed by 1H Wideline NMR and was attributed to chain branching and mobile crystalline domains respectively. This was supported by CLSM micrographs. All waxes enhanced crystallinity in both metallocene catalysed polyethylene (mPE) and ethylene-vinyl acetate (EVA) based HMAs. This was confirmed by the characteristic splitting in FTIR bands and increased DSC enthalpies observed for the HMA relative to the neat polymers. Of the formulations containing high melting waxes, FT wax resulted in HMAs with narrower crystallization profiles, an important factor in determining HMA set times. HMA viscosities were found to be dependent on the molecular weight of the wax while the HMA melting temperatures and enthalpies were more dependent on the crystalline morphology of the waxes.

Ultra-broad molecular weight distribution effects on viscoelastic properties of linear multimodal PE

Rheological investigation of polyethylene (PE) blends with a significant amount (up to 50 wt. %) of ultrahigh molecular weight PE (UHMWPE, with weight average molecular weight Mw > 106 g/mol) was not accessible so far. The development of special Enders catalysts allows the synthesis of such homogeneous PE reactor blends (RBs). In this paper, by melt blending of RBs with high-density PE polymer matrix, multimodal PE blends were prepared and their rheological properties were investigated. The analysis grants access to better understand how notably high amount of UHMWPE and ultra-broad molecular weight distribution displaying extremely high polydispersity, Ð ∼ 1000, influence the linear viscoelasticity. Moreover, taking advantage of the opportunities offered by molecular models, applying the tube-based time-marching algorithm, the “rheological” molecular weight distribution (MWD) of multimodal PE blends was determined, overcoming drawbacks of high-temperature size exclusion chromatography. Analyzing the zero-shear viscosity, η 0, versus Mw scaling relation for blends of any MWD, a correction scheme was developed which allows to take into account the Ð effects on η 0 properly. The analysis revealed that in a double logarithmic plot versus Mw, corrected η 0 shows a unique linear dependency with a slope of 3.6 if Mw is smaller than the reptation molecular weight (Mr). If Mw > Mr, the slope of this linear dependency turns into 3. The analysis of transition zone between the two linear dependencies allowed the experimental determination of PEs Mr.

Studies on the use of filter-based IR detector for short-chain branching characterization of polyolefin copolymers with high temperature size exclusion chromatography

Even though polyolefins are simple polymers from chemical structure point of view, their full characterization in practice is still an intriguing task. Basic macromolecular characteristics of polyethylene or polypropylene like molar mass moments and their distributions (MMD) but also chain conformation and thus information on long-chain branching, can be addressed with high-temperature size-exclusion chromatography (HT-SEC). Hyphenation of infrared detection to size-exclusion chromatography expands possibilities of SEC even more and allows to reveal comonomer incorporation across molecular weight and thus help in the study of catalytic systems used in polyolefin synthesis.Multiband filter-based infrared detector gives an easy and fast access to so-called short chain branching distribution (SCB) vs MMD by coupling to HT-SEC. In our previous work [31], we summarize recent findings on application of a filter-based detector towards characterization of polyolefins synthesized with different catalytic systems and varying comonomer types. In this work, an influence of the comonomer type on the detector calibration line is elaborated. Statistical evaluation of different calibration lines is discussed in detail. Based on this evaluation practical aspects of filter-based IR detectors calibration are mentioned. Finally, numerical computer simulations can predict how much calibration lines deviate from linearity based on the spectra of the polymer and on the bandwidth of the detector filters.

From Lab to Pilot Scale: Melt Electrospun Nanofibers of Polypropylene with Conductive Additives

In this paper, the feasibility of fabricating polypropylene (PP) nanofibers was investigated using conductive additives such as sodium stearate (NaSt), sodium oleate (NaOl) and Irgastat during melt electro spinning with a single nozzle lab and a 600- nozzle pilot scale device. Varying PP grades of high melt flow indices (MFI=450-1200 g/10 min) were used with different amounts of additives. The effects of the additives on the fiber diameters, thermal properties, electrical conductivity and polymer degradation were investigated. On a lab scale, fiber diameters of less than 500 nm were achieved with the compound of PP HL712FB, 4 wt% NaSt and 2 wt% Irgastat. The lab scale device was extended by a heatable spinning chamber, which affects fiber diameter reduction. The fabrication of nanofibers was in principle attributed to the increase in electrical conductivity with the introduction of the additives. On a pilot scale, the smallest fiber diameter of 6.64 μm could be achieved with PP HL508FB and 2 wt% NaSt. The comparison between the production of the fibers with a single nozzle and the pilot scale plant has revealed that a transfer of results is not possible without further ado. Due to the higher dwell time in the nozzle, a strong thermal degradation of the polymer could be detected with the high temperature size exclusion chromatography, whereby NaOl had the strongest influence on the thermal degradation. The high melt flow PP HL712FB and its compounds could not be processed with the pilot scale device due to its low viscosity, resulting in an insufficient pressure built up within the spinneret. Another reason for the non-spinnability of the material is the higher thermal and mechanical stress caused by the preceding melts preparation in an extrusion step. Further adjustments to the pilot plant are necessary to ensure a constant temperature distribution in the nozzle plate to achieve uniform fiber cross sections. The implementation of an uneven collector has successfully led to an even deposition of the fibers to obtain an isotropic non-woven fabric.

Polymer Identification of Plastic Debris Ingested by Pelagic-Phase Sea Turtles in the Central Pacific

Pelagic Pacific sea turtles eat relatively large quantities of plastic (median 5 g in gut). Using Fourier transform infrared spectroscopy, we identified the polymers ingested by 37 olive ridley, 9 green, and 4 loggerhead turtles caught as bycatch in Hawaii- and American Samoa-based longline fisheries. Unidentifiable samples were analyzed using high-temperature size exclusion chromatography with multiple detectors and/or X-ray photoelectron spectroscopy. Regardless of species differences in dive depths and foraging strategies, ingested plastics were primarily low-density, floating polymers (51% low-density polyethylene (LDPE), 26% polypropylene (PP), 10% unknown polyethylene (PE), and 5% high-density PE collectively). Albeit not statistically significant, deeper diving and deeper captured olive ridley turtles ate proportionally more plastics expected to sink (3.9%) than intermediate-diving green (1.2%) and shallow-diving loggerhead (0.3%) turtles. Spatial, but no sex, size, year, or hook depth differences were observed in polymer composition. LDPE and PP, some of the most produced and least recycled polymers worldwide, account for the largest percentage of plastic eaten by sea turtles in this region. These novel data inform managers about the threat of plastic ingestion to sea turtles and may motivate development of more environmentally friendly practices for plastic production, use, and waste management.

High Temperature Quadruple-Detector Size Exclusion Chromatography for Topological Characterization of Polyethylene.

Modifying material properties in simple macromolecules such as polyethylene (PE) is achieved by different connection modes of ethylene monomers resulting in a plurality of possible topologies-from highly linear to dendritic species. However, the challenge still lies within the experimental identification of the topology and conformation of the isolated macromolecules because of their low solubility, which demands methods with specific solvents and high operating temperatures. Additionally, a separation technique has to be coupled to different detection methods to meet the specific demands of the respective characterization goal. In this work, we report a quadruple-detector high temperature size exclusion chromatography (HT-SEC) system which contains online multiangle laser light scattering, dynamic light scattering, differential viscometry, and differential refractometry detectors. Quadruple-detector HT-SEC was successfully applied to explore the full range of physical parameters of various PE samples with different branching topologies ranging from highly linear macromolecules, polymers with moderate level of branching, to highly branched PEs with hyperbranched structure. This method is a useful tool not only to investigate molecular weight, mass distribution, and size but also to enable access to important factors which describe the conformation in dilute solution and branching density.

A multidimensional fractionation protocol for the oligomer analysis of oxidized waxes

Oxidized waxes possess far superior properties as compared to the alkanes they are derived from. The separation of alkane oligomers via gas chromatography (GC) becomes a challenge when polar oxygen-containing functional groups are introduced or when higher molar masses are targeted. In the present study, the separation and analysis of oligomers in oxidized and non-oxidized waxes using different liquid chromatographic techniques are investigated. Oligomers in two oxidized waxes and a non-oxidized wax from which they are derived, are separated using high-temperature solvent gradient interaction chromatography (HT-SGIC) and high-temperature two-dimensional liquid chromatography (HT-2D-LC). Evaporative light scattering detector conditions are tailored to provide the best detection with the solvent system at use. It is shown that oligomers in oxidized and non-oxidized waxes can be separated and identified using the mentioned techniques. It has been found that the ELSD detector response systematically decreases as the oxidation levels of the waxes increase. Coupling of HT-HPLC and high-temperature size exclusion chromatography (HT-SEC) in a comprehensive 2D-LC setup shows a broadening of the molar mass distributions of the lower oligomer fractions as a consequence of the modification indicating changes in the oligomer chain microstructures. A preparative fractionation technique is utilized to collect specific oligomer fractions from the bulk waxes followed by hyphenation to HT-HPLC and other techniques. HPLC is shown to provide more detailed information on the oligomer composition of waxes when coupled to a pre-fractionation technique.

Validation of ATR FT-IR to identify polymers of plastic marine debris, including those ingested by marine organisms

Polymer identification of plastic marine debris can help identify its sources, degradation, and fate. We optimized and validated a fast, simple, and accessible technique, attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), to identify polymers contained in plastic ingested by sea turtles. Spectra of consumer good items with known resin identification codes #1–6 and several #7 plastics were compared to standard and raw manufactured polymers. High temperature size exclusion chromatography measurements confirmed ATR FT-IR could differentiate these polymers. High-density (HDPE) and low-density polyethylene (LDPE) discrimination is challenging but a clear step-by-step guide is provided that identified 78% of ingested PE samples. The optimal cleaning methods consisted of wiping ingested pieces with water or cutting. Of 828 ingested plastics pieces from 50 Pacific sea turtles, 96% were identified by ATR FT-IR as HDPE, LDPE, unknown PE, polypropylene (PP), PE and PP mixtures, polystyrene, polyvinyl chloride, and nylon.

Separation of maleic anhydride grafted polypropylene using multidimensional high-temperature liquid chromatography

Functionalization addresses a property gap of polyolefins and opens new perspectives due to improved surface properties in applications like composites (e.g., glass fiber reinforced polypropylene) and anti-corrosive coatings for metals. Various techniques have been developed to characterize functionalized polyolefins, yet no analytical approach addressing their chemical heterogeneity exists. Using High Temperature Size Exclusion Chromatography (HT-SEC) coupled to infrared spectroscopy we could show for two model samples of polypropylene grafted maleic anhydride (PP-g-MA), differing in their nominal MA content, that the grafting density increases with decreasing molar mass. Crystallization Analysis Fractionation (CRYSTAF) does not enable to separate these samples according to their composition to the extent required. Yet, when using High Temperature High Performance Liquid Chromatography (HT-HPLC), with either silica gel or Mica as stationary phase and a gradient mobile phase, a deformulation into a grafted and a non-grafted fraction could be achieved. This was confirmed by analyzing the eluted fractions by infrared spectroscopy. Hyphenating the separation according to composition with a separation according to molar mass (HT-HPLC x HT-SEC) enabled for the first time to reveal the bivariate distribution of PP-g-MA with regard to the molar mass and composition. Using on-line infrared detection quantitative information on the compositional and molar mass parameters of the individual fractions could be obtained.

Studies on the Application of Filter‐Based IR Detector for Polyolefin Characterization with HT‐SEC

SummaryEven though polyolefins are simple polymers from a chemical structure point of view, their full characterization in practice is still an intriguing task. Basic macromolecular characteristics of polyethylene or polypropylene like molar mass moments and their distributions (MMD) but also chain conformation and thus information on long‐chain branching, can be addressed with high‐temperature size‐exclusion chromatography (HT‐SEC). Hyphenation of infrared detection to size‐exclusion chromatography expands possibilities of SEC even more and allows to reveal comonomer incorporation across molecular weight and thus generate a fingerprint of a given catalytic system used in polyolefin synthesis. Multiband filter‐based infrared detector gives an easy and fast access to so‐called short chain branching distribution (SCB) vs MMD by coupling to HT‐SEC. In this work, we summarize recent findings on application of a filter‐based IR detector (IR5‐MCT) towards characterization of polyolefins synthesized with different catalytic systems and varying comonomer types. It is found that for copolymers of polyethylene with 1‐butene, 1‐hexene or 1‐octene (non‐C3), one linear calibration line can be used in the range up to 70 CH3/1000TC, thus covering the range necessary for common applications like for instance HDPE or LLDPE. For ethylene‐propylene copolymers (C3), over the broad range up to 333 CH3/1000TC, the calibration line is best fitted to a second order polynomial. C3 copolymers show a different behavior compared to non‐C3 copolymers, irrespective the amount of comonomer incorporated in the polymer. We show that mixtures of PP and PE homopolymers result in equivalent response as the copolymers of the same average composition and thus can also be used to set up calibration lines. Based on this evaluation practical aspects of IR5‐MCT calibration are discussed.

On the multimodality of preparative TREF fractionation as detected by advanced analytical methods.

Preparative temperature rising elution fractionation (prepTREF) is the standard technique for the preparative fractionation of polyolefins according to crystallisability. For olefin copolymers such as linear low-density polyethylene (LLDPE), it was believed that the TREF elution temperature correlates directly with the copolymer composition. For copolymers having different bulk comonomer contents, the prepTREF fractions of different samples collected at a given temperature were assumed to have the same chemical composition. It was acknowledged quite early that co-crystallisation effects may disturb TREF fractionation and fractions are obtained that are not completely homogeneous. This, however, has not been investigated quantitatively so far. The fundamental statement of prepTREF is challenged for the first time quantitatively using advanced analytical techniques including high-temperature high-performance liquid chromatography (HPLC). Ethylene-1-octene copolymers having bulk comonomer contents ranging from 0.3 to 6.4mol% were fractionated by prepTREF, and the fractions were analysed by high-temperature size exclusion chromatography, crystallisation analysis fractionation, differential scanning calorimetry and high-temperature HPLC. All analytical results prove that the TREF fractions collected from different samples at the same elution temperature have different chemical compositions. The chemical compositions of the fractions correlate with the compositions of the bulk samples in that the comonomer contents of similar TREF fractions increase with an increase of the comonomer content of the bulk samples. These results are in clear contrast to the previous assumption that the TREF fraction composition is independent of the bulk copolymer composition for a given copolymer type. Graphical abstract Advanced analysis of LLDPE by combination of HT-HPLC, DSC and CRYSTAF.