Synthesis of Highly Branched Polystyrene Model Systems with Superior Strain Hardening and their Influence on Foaming Properties

Die molekulare Struktur bestimmt maßgeblich die Verarbeitbarkeit eines Polymers in der Schmelze und die daraus resultierenden makroskopischen Eigenschaften des Endprodukts, die wiederum über seine Anwendung entscheiden. Viele dieser Anwendungen beruhen auf dünnen Film- und Faserstrukturen, von denen polymere Schäume mit ihrer porösen Zellmorphologie ein wichtiger Vertreter sind. Die Schmelzefestigkeit ist entscheidend für die Expandierbarkeit eines Schaums, da sie die Zellwände und Verstrebungen auf mikro- und nanoskaliger Ebene stabilisiert. Verzweigungen, insbesondere Langkettenverzweigungen sind eine Schlüsseleigenschaft eines Polymers um eine gute Schmelzefestigkeit in Dehnströmung zu erreichen. Es ist von großem Interesse, den Einfluss der Topologie eines Polymers auf das rheologische Verhalten zu verstehen und die Struktur-Eigenschafts-Beziehung vorherzusagen und letztendlich effizient zu nutzen. Die hier vorgestellte Arbeit untersucht den Einfluss von mehrfach verzweigten Polymerarchitekturen auf die Schäumbarkeit, speziell auf die Volumenexpansion und korreliert die erzielten Schaumeigenschaften mit der Molekularstruktur mittels dem Fließverhalten aus der Scher- und Dehnrheologie. Um einen systematischen Ansatz zu ermöglichen, werden definierte Modellpolystyrole (PS) mit Kamm- und Dendrigraft-Topologie und einer variierenden Anzahl von Verzweigungen mittels anionischer Synthese hergestellt. Die Schmelzeeigenschaften werden in oszillatorischer Scherung und uniaxialer Dehnung rheologisch charakterisiert. Das Batch-Schäumen wird bei $180$ und $500\,\text{bar}$ unter Verwendung von Kohlendioxid (CO$_2$) als physikalisches Treibmittel durchgeführt. Die resultierenden Schäume werden hinsichtlich ihrer Volumenausdehnung, Zellgröße und Zelldichte analysiert. Es wird eine Reihe von Kamm-PS mit gut verzweigten, aber unterschiedlicher Anzahl von Langkettenverzweigungen synthetisiert, die von spärlich verzweigt bis hin zu flaschenbürstenartiger Strukturen reichen. Die Korrelation der rheologischen und der Schaumeigenschaften zeigt einen Bereich optimaler Verzweigungszahl, die in einen maximalen Volumenexpansionskoeffizient von 40 bei gleichzeitig maximalem Dehnverfestigungsfaktor (\textit{strain hardening factor}) von $\text{SHF}=200$ resultiert, wobei die Nullscherviskosität auch am niedrigsten ist. Dendrigraft-PS werden aus einem langkettenverzweigten Kamm-PS synthetisiert, auf den eine Korona aus Kurzkettenverzweigungen aufgepfropft wird. Die sogenannte ``branch-on-Branch\u27\u27 (bob)-Architektur weist molekulare Parameter auf, die eindeutig drei verschiedene Relaxationsmodi zeigen, die jeder Verzweigungsgeneration zugeordnet werden können und auf die hierarchische Kettendynamik hinweisen. In uniaxialer Dehnung wird ein enormer Dehnungsverfestigungfaktor bis zu $\text{SHF}=700$ erreicht. Dabei zeigt sich die Dehnrate als ein wichtiges Kriterium dafür, ob eine hohe Dehnverfestigung zu einer verbesserten Schäumbarkeit führt. Dies wird durch das Schäumen eines kurzkettenverzweigten Kamm-PS validiert, der sich durch eine Dehnverfestigung von $\text{SHF}=200$ bei schnellen Dehnungsraten von $\dot\varepsilon_\text{H}=3\text{--}10\,\text{s}^{-1}$ auszeichnet und im Vergleich zu Dendrigraft- und langkettenverzweigten Kamm-PS konstant höhere Volumenexpansionen liefert, insbesondere bei hohen Schäumungstemperaturen und schnellen Druckentlastungsraten. Weiterhin werden bimodale Kamm-Lineare PS-Blends hergestellt, um das Zusammenspiel zwischen verzweigter und linearer Kettentopologie zu untersuchen. Die Schmelzrheologie gibt einen Einblick in Relaxationsdynamiken und deren Skalengesetze und zeigt das Potenzial von verzweigt-linearen Blends zur Einstellung und Optimierung der Schmelzeeigenschaften für Verarbeitungsprozesse in Dehnung oder Scherung

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

Comb and bottlebrush polymers present a wide range of rheological and mechanical properties that can be controlled through their molecular characteristics, such as the backbone and side chain lengths as well as the number of branches per molecule or the grafting density. This review investigates the impact of these characteristics specifically on the zero shear viscosity, strain hardening behavior, and plateau shear modulus. It is shown that for a comb polymer with an entangled backbone and entangled side chains, a maximum in the strain hardening factor and minimum in the zero shear viscosity η$_{0}$ can be achieved through selection of an optimum number of branches q. Bottlebrush polymers with flexible filaments and extremely low plateau shear moduli relative to linear polymers open the door for a new class of solvent‐free supersoft elastomers, where their network modulus can be controlled through both the degree of polymerization between crosslinks, n$_{x}$, and the length of the side chains, n$_{sc}$, with G$^{0}$$_{BB}$≈ρkTn$_{x}$$^{−1}$(n$_{sc}$+1)$^{−1}$

Comb and Branch‐on‐Branch Model Polystyrenes with Exceptionally High Strain Hardening Factor SHF > 1000 and Their Impact on Physical Foaming

The influence of topology on the strain hardening in uniaxial elongation is investigated using monodisperse comb and dendrigraft model polystyrenes (PS) synthesized via living anionic polymerization. A backbone with a molecular weight of M$_{w,bb}$ = 310 kg mol$^{–1}$ is used for all materials, while a number of 100 short (SCB, M$_{w,scb}$ = 15 kg mol$^{–1}$) or long chain branches (LCB, M$_{w,lcb}$ = 40 kg mol$^{–1}$) are grafted onto the backbone. The synthesized LCB comb serves as precursor for the dendrigraft-type branch-on-branch (bob) structures to add a second generation of branches (SCB, M$_{w,scb}$ ≈ 14 kg mol$^{–1}$) that is varied in number from 120 to 460. The SCB and LCB combs achieve remarkable strain hardening factors (SHF) of around 200 at strain rates greater than 0.1 s$^{–1}$. In contrast, the bob PS reach exceptionally high SHF of 1750 at very low strain rates of 0.005 s$^{–1}$ using a tilted sample placement to extend the maximum Hencky strain from 4 to 6. To the best of the authors’ knowledge, SHF this high have never been reported for polymer melts. Furthermore, the batch foaming with CO$_{2}$ is investigated and the volume expansions of the resulting polymer foams are correlated to the uniaxial elongational properties

An approach to build an event set of European wind storms based on ECMWF EPS

The properties of European wind storms under present climate conditions are estimated on the basis of surface wind forecasts from the European Center of Medium-Range Weather Forecast (ECMWF) Ensemble Prediction System (EPS). While the EPS is designed to provide forecast information of the range of possible weather developments starting from the observed state of weather, we use its archive in a climatological context. It provides a large number of modifications of observed storm events, and includes storms that did not occur in reality. Thus it is possible to create a large sample of storm events, which entirely originate from a physically consistent model, whose ensemble spread represents feasible alternative storm realizations of the covered period. This paper shows that the huge amount of identifiable events in the EPS is applicable to reduce uncertainties in a wide range of fields of research focusing on winter storms. Wind storms are identified and tracked in this study over their lifetime using an algorithm, based on the local exceedance of the 98th percentile of instantaneous 10 m wind speed, calculating a storm severity measure. After removing inhomogeneities in the dataset arising from major modifications of the operational system, the distributions of storm severity, storm size and storm duration are computed. The overall principal properties of the homogenized EPS storm data set are in good agreement with storms from the ERA-Interim dataset, making it suitable for climatological investigations of these extreme events. A demonstrated benefit in the climatological context by the EPS is presented. It gives a clear evidence of a linear increase of maximum storm intensity and wind field size with storm duration. This relation is not recognizable from a sparse ERA-Interim sample for long lasting events, as the number of events in the reanalysis is not sufficient to represent these characteristics

Small and Medium Amplitude Oscillatory Shear Rheology of Model Branched Polystyrene (PS) Melts

Linear and nonlinear rheological properties of model comb polystyrenes (PS) with loosely to densely grafted architectures were measured under small and medium amplitude oscillatory shear (SAOS and MAOS) flow. This comb PS set had the same length of backbone and branches but varied in the number of branches from 3 to 120 branches. Linear viscoelastic properties of the comb PS were compared with the hierarchical model predictions. The model underpredicted zero-shear viscosity and backbone plateau modulus of densely branched comb with 60 or 120 branches because the model does not include the effect of side chain crowding. First- and third-harmonic nonlinearities reflected the hierarchy in the relaxation motion of comb structures. Notably, the low-frequency plateau values of first-harmonic MAOS moduli scaled with M$^{-2}$$_{w}$ (total molecular weight), reflecting dynamic tube dilution (DTD) by relaxed branches. Relative intrinsic nonlinearity Q$_{0}$ exhibited the difference between comb and bottlebrush via no low-frequency Q$_{0}$ peak of bottlebrush corresponding to backbone relaxation, which is probably related to the stretched backbone conformation in bottlebrush

The genomic and transcriptional landscape of primary central nervous system lymphoma

Primary lymphomas of the central nervous system (PCNSL) are mainly diffuse large B-cell lymphomas (DLBCLs) confined to the central nervous system (CNS). Molecular drivers of PCNSL have not been fully elucidated. Here, we profile and compare the whole-genome and transcriptome landscape of 51 CNS lymphomas (CNSL) to 39 follicular lymphoma and 36 DLBCL cases outside the CNS. We find recurrent mutations in JAK-STAT, NFkB, and B-cell receptor signaling pathways, including hallmark mutations in MYD88 L265P (67%) and CD79B (63%), and CDKN2A deletions (83%). PCNSLs exhibit significantly more focal deletions of HLA-D (6p21) locus as a potential mechanism of immune evasion. Mutational signatures correlating with DNA replication and mitosis are significantly enriched in PCNSL. TERT gene expression is significantly higher in PCNSL compared to activated B-cell (ABC)-DLBCL. Transcriptome analysis clearly distinguishes PCNSL and systemic DLBCL into distinct molecular subtypes. Epstein-Barr virus (EBV)+ CNSL cases lack recurrent mutational hotspots apart from IG and HLA-DRB loci. We show that PCNSL can be clearly distinguished from DLBCL, having distinct expression profiles, IG expression and translocation patterns, as well as specific combinations of genetic alterations

Monocytes, neutrophils, and platelets cooperate to initiate and propagate venous thrombosis in mice in vivo

Deep vein thrombosis (DVT) is a major cause of cardiovascular death. The sequence of events that promote DVT remains obscure, largely as a result of the lack of an appropriate rodent model. We describe a novel mouse model of DVT which reproduces a frequent trigger and resembles the time course, histological features, and clinical presentation of DVT in humans. We demonstrate by intravital two-photon and epifluorescence microscopy that blood monocytes and neutrophils crawling along and adhering to the venous endothelium provide the initiating stimulus for DVT development. Using conditional mutants and bone marrow chimeras, we show that intravascular activation of the extrinsic pathway of coagulation via tissue factor (TF) derived from myeloid leukocytes causes the extensive intraluminal fibrin formation characteristic of DVT. We demonstrate that thrombus-resident neutrophils are indispensable for subsequent DVT propagation by binding factor XII (FXII) and by supporting its activation through the release of neutrophil extracellular traps (NETs). Correspondingly, neutropenia, genetic ablation of FXII, or disintegration of NETs each confers protection against DVT amplification. Platelets associate with innate immune cells via glycoprotein Ibα and contribute to DVT progression by promoting leukocyte recruitment and stimulating neutrophil-dependent coagulation. Hence, we identified a cross talk between monocytes, neutrophils, and platelets responsible for the initiation and amplification of DVT and for inducing its unique clinical features

Motor skill learning in the middle-aged: limited development of motor chunks and explicit sequence knowledge

The present study examined whether middle-aged participants, like young adults, learn movement patterns by preparing and executing integrated sequence representations (i.e., motor chunks) that eliminate the need for external guidance of individual movements. Twenty-four middle-aged participants (aged 55–62) practiced two fixed key press sequences, one including three and one including six key presses in the discrete sequence production task. Their performance was compared with that of 24 young adults (aged 18–28). In the middle-aged participants motor chunks as well as explicit sequence knowledge appeared to be less developed than in the young adults. This held especially with respect to the unstructured 6-key sequences in which most middle-aged did not develop independence of the key-specific stimuli and learning seems to have been based on associative learning. These results are in line with the notion that sequence learning involves several mechanisms and that aging affects the relative contribution of these mechanisms

Evaluating Effects of Divided Hemispheric Processing on Word Recognition in Foveal and Extrafoveal Displays: The Evidence from Arabic

Background: Previous studies have claimed that a precise split at the vertical midline of each fovea causes all words to the left and right of fixation to project to the opposite, contralateral hemisphere, and this division in hemispheric processing has considerable consequences for foveal word recognition. However, research in this area is dominated by the use of stimuli from Latinate languages, which may induce specific effects on performance. Consequently, we report two experiments using stimuli from a fundamentally different, non-Latinate language (Arabic) that offers an alternative way of revealing effects of split-foveal processing, if they exist. Methods and Findings: Words (and pseudowords) were presented to the left or right of fixation, either close to fixation and entirely within foveal vision, or further from fixation and entirely within extrafoveal vision. Fixation location and stimulus presentations were carefully controlled using an eye-tracker linked to a fixation-contingent display. To assess word recognition, Experiment 1 used the Reicher-Wheeler task and Experiment 2 used the lexical decision task. Results: Performance in both experiments indicated a functional division in hemispheric processing for words in extrafoveal locations (in recognition accuracy in Experiment 1 and in reaction times and error rates in Experiment 2) but no such division for words in foveal locations. Conclusions: These findings from a non-Latinate language provide new evidence that although a functional division i