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As commodity plastics, polyolefins are in high demand and used in innumerable applications. An important reason for their success-story is their high versatility in terms of applications. The application range of polyolefins was significantly extended through the development of functionalization. A common functionalization for improving the compatibility of polyolefins with more polar polymers and surfaces is grafting with maleic anhydride. While maleic anhydride-grafted polyolefins have found widespread application, methods for their characterization remain rudimentary compared to the developments seen in the structural characterization of polyolefins in general. Herein, we propose two new approaches for determining the degree of functionalization as a function of the molar mass of maleic anhydride grafted polyolefins. On the one hand, the latest generation bandpass filter-based IR detectors are shown to be sensitive to the carbonyl moiety of MAH. After optimization of analysis conditions, the relation between MAH content and molar mass could be unraveled in an easily applicable approach suitable for routine analysis. On the other hand, the high reactivity of MAH was leveraged in a tagging approach. By imidization with a UV chromophore, MAH distribution can be assessed by HT-GPC-UV with significantly higher sensitivity compared to HT-GPC-IR., 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. Published by Elsevier B.V.)

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., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jan-Hendrik Arndt reports financial support was provided by Braskem SA. Guru Geertz reports financial support was provided by Braskem SA. Robert Bruell reports financial support was provided by Braskem SA. Sampat Singh Bhati reports a relationship with Braskem Europe that includes: employment. Hadi Mohammadi, Manoela Ellwanger Cangussu has patent #WO 2021/064,474 A1 issued to Braskem SA., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Liquid chromatography at critical conditions is of interest as it may unravel molecular information on macromolecular structures not accessible by any other analytical techniques. Yet so far, such conditions have never been experimentally established for copolymers, where a particular need for such information exists. Toward this goal, critical conditions for statistical ethylene propylene copolymers were identified. In the first approach the composition of the binary mobile phase was varied at a constant temperature, and secondly by modulating the adsorption-desorption temperature at constant mobile phase composition. Solvents for both methods were identified by using a novel approach that combines structure retention relationships with Hansen Solubility Parameters. As a result, for the first time, the heterogeneity of an ethylene propylene diene terpolymer sample with regard to the pendant double bond of the diene could be determined. The novel chromatographic approach was validated by measuring the composition of fractions taken over the chromatographic run offline by nuclear magnetic resonance. In summary, this work gave the first experimental evidence for the existence of critical conditions for polyolefin random copolymers, as postulated by Brun. This novel chromatographic approach holds immense potential to engineer complex polymers towards future applications by making use of the now-accessible molecular information., 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 Elsevier B.V. All rights reserved.)

The elution behavior of ethylene-norbornene (EN) copolymers prepared with various catalysts was studied in selected binary solvent gradients using porous graphite (Hypercarb TM ) as stationary phase. It was found that the elution volumes of the EN copolymers correlated with their average norbornene content. For a series with norbornene content lower than 20 mol % the correlation was positive (i.e. increasing elution volumes with increasing norbornene content), whereas for a series with norbornene contents above 20 mol % it was negative (decreasing elution volumes with increasing norbornene content). It is known that EN copolymers have complicated microstructures that depend on norbornene content and the catalyst system used for synthesis. Thus, it is supposed that the opposing trends in the elution behavior of the EN copolymers are caused by differences in their microstructure, ultimately governed by the norbornene content. Our conclusions are supported by results from NMR spectroscopy, which revealed the microstructure, and differential scanning calorimetry (DSC)., 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 © 2021. Published by Elsevier B.V.)

The extraction of different stabilizers from a polymer matrix and the subsequent separation of said stabilizers is one of the most important as well as challenging undertakings in polymer chemistry. A multitude of stabilizers exists, each of which may be hard to extract, be difficult if not impossible to separate from other stabilizers or necessitate very selected and time-consuming intermediate stages for separation. Certain polymer matrices even pose additional challenges, such as polyolefins being only soluble at elevated temperatures. One of the most well-established approaches for the extraction of stabilizers is Soxhlet extraction. However, even this highly successful approach shows only limited success with regard to the extraction of the ever more relevant oligomeric stabilizers or the extraction of multiple stabilizers in a one-shot approach. Moreover, performing Soxhlet extractions often necessitates ≥24 h. For these reasons, alternative approaches for the extraction of stabilizers from polymers are highly sought after. An approach with enormous potential is solid-phase extraction, which allows the selective retention and enrichment of stabilizers. Herein, the very first application of high-temperature solid-phase extraction for the extraction of stabilizers from polyolefin matrices is described; as with other extraction techniques, the identification and quantification of the stabilizers is then allowed. At temperatures of 140-160°C, it was possible to adsorb common polyolefin stabilizers selectively on a silica solid phase from their polyolefin matrix. To predict high-temperature solid-phase extraction test conditions, first LC tests are necessary, offering an elegant approach for the separation of polyolefins from oligomeric stabilizers, which was not achievable until now., (© 2021 The Authors. Journal of Separation Science published by Wiley-VCH GmbH.)

The compositional and stereochemical heterogeneity of copolymers are key molecular metrics, and their knowledge is of pivotal importance for evidence based material development. Yet, while it is state of the art to determine these parameters for many petroleum based polymers, little insight exists in that regard for bio-based materials. Towards this end, size exclusion chromatography (SEC) was hyphenated with nuclear magnetic resonance spectroscopy (NMR) in an offline manner and a blend of poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) investigated. Thus, the microstructural heterogeneity could be shown with regard to tacticity of the PLA and regioregularity of the PBSA component. The results show, that the highest molar mass fraction differs in stereochemical composition from the others. It may be assumed that this is the result of misinsertions with regard to stereochemistry occurring during the catalytic polymerization of the lactide. While the content of both constituent polymers along the molar mass axis could be well studied using a univariate analysis of the infrared (IR) spectra, this method failed to profile the adipate and succinate content individually. For this purpose, SEC was coupled to IR spectroscopy in online mode and the spectra were evaluated by a multivariate protocol. Thus, the content of each monomer along the molar mass distribution could be mapped with high chromatographic resolution., 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 © 2020. Published by Elsevier B.V.)

Additives are added to polymers in small concentration to achieve desired application properties widely used to tailor the properties. The rapid diversification of their molecular structures, with often only minute differences, necessitates the development of adequate chromatographic techniques. While modified silica so far is the workhorse as stationary phase we have probed the potential of porous graphitic carbon (Hypercarb TM ) for this purpose. The results show that the multitude of physicochemical interactions between analyte molecules and the graphitic surface enables separations of polyolefin stabilizers with unprecedented selectivity. To support the chromatographic results the adsorption capability of Hypercarb TM for selected antioxidants and UV absorbers has been determined by Raman spectroscopy and argon physisorption measurements. The shift of the Graphite-band in the Raman spectra of Hypercarb TM upon infusion with additives correlates with the changes in the Adsorption Potential Distributions. The results of argon physisorption measurements go hand in hand with the chronology of desorption of the additives in liquid chromatography experiments. The elution sequence can be explained by van der Waals or London forces, π-π-interactions and electron lone pair donor-acceptor interactions between the graphite surface and analyte functional groups., 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 © 2020. Published by Elsevier B.V.)

The chemical composition distribution (CCD) of three single site made ethylene/1-octene copolymers was investigated through offline-hyphenation of solvent gradient interaction chromatography (SGIC) with 1 H NMR. Thus, a clear, non-linear correlation between SGIC elution time and chemical composition was found under the specific measurement conditions applied here. The application of 1 H NMR as detection allowed to determine the CCD with unprecedented accuracy. 2D-LC of the copolymers revealed the correlation between CCD and molar mass distribution (MMD) in a quantitative manner. Furthermore, this approach allowed a comparison between the response behavior of an evaporative light scattering detector (ELSD, semi-quantitative, commonly applied in SGIC) and that of an infrared (IR) detector (quantitative, commonly applied in SEC). As a result, it could be shown that ELSD results are close to IR results for the system investigated here, in other words, the often-criticized semi-quantitative response behavior of the ELSD is affecting results in an acceptable manner., 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 © 2020 Elsevier B.V. All rights reserved.)

Porous graphite as sorbent differs significantly from all other HPLC column packings. It stands out due to its chemically extremely homogeneous surface, which moreover is planar on an atomic level. This sorbent, according to its non-polar but polarizable surface, is able to adsorb polar as well as non-polar small molecules as well as macromolecules. Moreover, it enables their separation induced by minute differences in their molecular architecture, which includes the aspects of planarity, branching or tacticity of macromolecules. Although graphite had already been used many years for the separation of small molecules, the application of porous graphite for separations in the domain of synthetic polymers has been rare. In 2009 it was found that porous graphite enables the separation of polyethylene and polypropylene on the basis of their full adsorption and desorption, when suitable solvents are used. This approach has led to the fast elaboration of HPLC systems for separations of various polar modified as well as non-polar polyolefins. Due to pronounced adsorptive interactions, porous graphite is applicable even at temperatures as high as 160 °C. The results presented in this paper manifest that porous graphite enables to obtain important information about the composition distribution of various synthetic polymers, the architecture of macromolecules (i.e., branching) or their tacticity, and underlines its enormous application potential., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A series of ethylene/1-octene copolymers with different chemical composition was separated in six binary mobile phases using solvent gradients and a column packed with porous graphite Hypercarb ™ . It was found that the elution volumes of the samples were to a larger extent influenced by the choice of desorption promoting solvent (desorli: 1,2-dichlorobenzene vs. 1,2,4-trichlorobenzene) than by the choice of adsorption promoting solvent (2-ethyl-1-hexanol, 1-decanol, n-decane). Elution volumes increased with decreasing number of chlorine atoms in the desorlis as well as with increasing polarity of the adsorlis. The resolution of HPLC systems depended pronouncedly on the choice of solvent pair: While in the majority of the tested HPLC systems, the chromatograms of the polymer samples indicate a shoulder, in n-decane→TCB the samples eluted without indication of a shoulder. In addition to the influence of different solvents on the samples elution behavior, the response of the employed detector, an evaporative light scattering detector (ELSD), was investigated. Its response was found to depend pronouncedly on the nature of the used solvents. Overall, the solvent pair 1-decanol→TCB appears to be the optimal compromise between the considered parameters and thus the best choice for HPLC of ethylene/1-octene copolymers., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Over the last two decades the evaporative light scattering detector (ELSD) has found more and more use in liquid chromatography (LC) of synthetic polymers. The reason behind this is that it can be used for a significantly wider variety of analyte/solvent combinations. Although in many of the applications the ELSD has been used in a qualitative manner, it can also be used quantitatively. For quantitative interpretation of analyses it is, in the case of synthetic polymers, essential to know how parameters, which characterize a polymer sample (i.e., molar mass and chemical composition), as well as parameters, which are a consequence of the LC separation (i.e., composition and flow rate of the mobile phase, its composition), influence the response of the ELSD. This review gives a tabulated overview over applications of ELS detectors in polymer analysis. The influence of parameters arising from either the polymer side or the chromatographic separation is discussed in detail and, in addition, the influence of the ELS detector's running conditions, i.e. type and flow rate of gas and temperature of nebulizer and evaporator), will be reviewed. This information will prove valuable whenever the calibration of an ELSD for the quantitative analysis of synthetic polymers is attempted., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Rationale and Objectives: This survey was compiled to provide current data on the structure and content of radiology residency programs and the role of the residency program director., Methods: A survey, created in electronic form and on paper, was distributed to all United States academic, private, and military radiology residency program directors., Results: Of the 202 survey forms distributed, 168 (83%) were completed and returned. Eighty percent of respondents support national curriculum guidelines, but most do not favor national curriculum requirements. About half (53%) of programs spend 6 months in "view box" nuclear medicine; others provide some experience by lectures and on-call time. Most programs (60%) relieve residents of some call during the senior year. Some programs (28%) allow seniors time away from clinical duties to study for the oral board exam, and 17% permit time away to study for the written boards. Seventy-eight percent of programs have had a "problem resident," and 47% have asked a resident to leave the program. Directors' most frequently expressed concern was threat of diminished residency numbers due to decreased funding.

Studies with a camera and a model eye showed that the image produced by peripheral light rays is inferior to the image produced by paraxial rays. In a retrospective clinical study, we determined the best corrected visual acuity in 33 patients (52 eyes) who had had iridectomy (group I) or aspiration (group II) or both for central cataracts. Vision was significantly better (p less than 0.01) in group II than in group I, and postoperative complications of aspiration were minimal. Some patients had unilateral amblyopia or pendular nystagmus. We conclude that if vision is to be improved with a single procedure, aspiration - not optical iridectomy - is indicated. We could not identify any factors in early infancy that would have predicted which patients with congenital central cataracts required early surgery.