Ligand exchange reactions of aryl pyridyl sulfoxides with grignard reagents: Convenient preparation of 3- and 4-pyridyl grignard reagents and examination of the leaving abilities of pyridyl anions

Aryl 3- and 4-pyridyl sulfoxides undergo ligand exchange in reactions with aryl Grignard reagents to generate 3- and 4-pyridyl Grignard reagents, which, upon treatment with aldehydes or ketones, give the corresponding addition products in moderate-to-good yields. The mechanism for the exchange reaction was investigated by treating optically active 3- and 4-pyridyl p-tolyl sulfoxides with a phenyl Grignard reagent. Inversion of the configuration of the sulfur atom was the stereochemical result of the reactions. In the reactions of phenyl 2-pyridyl sulfoxide with Grignard reagents, the leaving ability of the 2-pyridyl group competes with that of the phenyl group. Both the experimental and MO calculated enthalpy values for deprotonation of α-, β-, and γ-protons of pyridine in the gas phase [1] are in accordance with the following order of the leaving abilities of aryl and pyridyl Grignard reagents: 4-PyMgBr > 3-PyMgBr » PhMgBr > p-TolMgBr > 2-PyMgBr.     

Dielectric studies on the dynamics of polymer chains in various environments

Stockmayer's type-A chain such as cis-polyisoprene (PI) having dipole moments aligned parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of the end-to-end vector of the chain ( dielectric normal modes ). This article intends to review our own work on dielectric spectroscopy using PI as a probe for studying dynamics of large scale motion of the probe chain in binary blends with polybutadiene (PB) and in block copolymers with PB or with polystyrene. Through such studies we were able to see the features of polymer chain dynamics in various environments: Rouse-Zimm-like dynamics in overlapping-but-unentangled regimes, reptation with and without accompanying constraint release, behaviour of a subchain incorporated into block copolymers with miscible segments, and dynamics of polymer brushes in strongly segregating block copolymers in bulk and in solutions.     

Donor–Acceptor Heterojunction Configurations Based on DNA–Multichromophore Arrays

Multichromophore arrays of bis(2‐thienyl)diketopyrrolopyrrole (DPP) and naphthalenediimide (NDI) with two Zn^II‐cyclens were constructed using thymidine DNA as a scaffold through the binding of the Zn^II‐cyclens with thymine bases. We demonstrate photocurrent generation in a donor–acceptor heterojunction configuration consisting of the DPP (donor) and NDI (acceptor) arrays co‐immobilized on an Au electrode. The co‐immobilized electrode exhibited good photocurrent responses because of the efficient charge separation between the DPP and NDI arrays. In contrast, an immobilized electrode consisting of randomly assembled DPP‐NDI arrays generated no photocurrent response because DPP formed ground‐state charge‐transfer complexes with NDI in the randomly assembled arrays. Therefore, our approach to generate donor–acceptor heterojunctions based on DNA–multichromophore arrays is a useful method to efficiently generate photocurrent.     

Utility of parallel-plate plastometer for rheological study of filled polymer melts

Summary In order to test the applicability of the parallel-plate plastometer to the rheological study of filled polymer melts, viscous properties of polyethylene and polystyrene filled with particles and short fibers were measured by this apparatus. Flow curves in the low range of shear rate were obtained by approximating the materials as Ostwald-de-Waele liquids. Up to about 0.5 of the volume fraction of the filler,, there was no problem and the utility of the apparatus was clearly shown. When increased more, the results were not necessarily self-consistent because the flow became unstable. Experiments on samples with high showed that the unstable flow resulted in an apparent yield stress which agreed with that estimated from the Casson's plots.

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Zusammenfassung Um die Anwendbarkeit des Parallel-Platten-Plastometers für die rheologische Untersuchung von Schmelzen gefüllter Polymerer zu prüfen, wurden mit einem solchen Gerät die viskosen Eigenschaften von Polyäthylen und Polystyrol-Proben gemessen, die mit Teilchen oder kurzen Fasern gefüllt waren. Im Bereich niedriger Schergeschwindigkeiten ließen sich die Fließkurven mit Hilfe der Ostwald-de Waele-Gleichung approximieren. Bis zu einer Füllstoff-Volumenkonzentration von etwa 50% traten keine Komplikationen auf, so daß die Eignung des Geräts für diese Fälle klar erwiesen werden konnte. Wenn jedoch noch weiter gesteigert wurde, waren die Ergebnisse durchweg nicht mehr widerspruchsfrei, da dann der Fließvorgang instabil wurde. Versuche mit hohen Volumenkonzentrationen zeigten, daß die Fließinstabilität eine scheinbare Fließgrenze zur Folge hat, deren Größe mit dem aus einer Casson-Darstellung abgeschätzten Wert in etwa übereinstimmt.

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With 8 figures and 1 table     

Non-Newtonian flow and normal stress phenomena in solutions of polystyrene in toluene

Summary Non-Newtonian flow and normal stress phenomena are studied with solutions of polystyrene in toluene with varying temperature, concentration and molecular weight.The temperature dependence of normal and shear stresses of a solution with fixed concentration can be described in terms of the shift factor,a _T , which is commonly used in the study of linear viscoelastic phenomena of polymeric systems.From the measurements of normal and shear stresses the elasticity contribution to flow behavior of polymer solution can be evaluated, and its dependences on concentration and molecular weight are discussed. Each of the tested solutions shows more or less non-Newtonian viscosity behavior, especially very strongly in solutions with high concentration and high molecular weight. And these solutions are mainly Hookean in shear, but non-Hookean character appears in solutions with high concentration and with rather low molecular weight.The zeroshear viscosityversus concentration relationship is found to obey ac ⁵-dependence in a certain range of concentration, while in the same concentration range the reciprocal of steady shear compliance shows ac ^1,5 c ²-dependence. The zeroshear viscosityversus molecular weight relationship of solutions at a fixed concentration obeys the well-knownM ^3,4-dependence above a certain critical value of molecular weight which is dependent on the concentration. While the reciprocal of compliance is almost independent of molecular weight above this value, and it seems to be somewhat affected by the type of polymers such as molecular weight heterogeneity and/or degree of branching of the polymer.

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Zusammenfassung Nicht-Newtonsches Fließen und Normalspannungsphänomene wurden an Lösungen von Polystyrol in Toluol bei verschiedenen Temperaturen und Konzentrationen sowie bei verschiedenem Molekulargewicht untersucht.Die Temperaturabhängigkeit der Normal- und Schubspannungen einer Lösung bestimmter Konzentration kann durch den Schift-Faktora _T , der allgemein bei der Betrachtung linearer viskoelastischer Phänomene polymerer Systeme gebraucht wird, beschrieben werden. Aus den Messungen der Normal- und Schubspannungen wurde der Elastizitätsbeitrag zu dem Fließverhalten der polymeren Lösung abgeleitet und seine Abhängigkeit von der Konzentration und dem Molekulargewicht diskutiert.Jede der geprüften Lösungen zeigte mehr oder weniger nicht-Newtonsches Viskositätsverhalten, besonders stark ausgeprägt in Lösungen mit hoher Konzentration und hohem Molekulargewicht. Die Lösungen zeigten bei Scherbeanspruchung hauptsächlichHookeschen Charakter. Der nicht-Hookesche Charakter trat eher auf in Lösungen mit hoher Konzentration und bei niedrigerem Molekulargewicht.Die Anfangsviskositäts-Konzentrationsbeziehunggehorcht einerc ⁵-Abhängigkeit in einem gewissen Konzentrationsbereich, während bei derselben Konzentration der reziproke Wert der Komplianz (Nachgiebigkeit) bei stationärem Scheren einec ^1,5- bisc ²-Abhängigkeit aufweist. Oberhalb eines gewissen kritischen Wertes des Molekulargewichts, der von der Konzentration abhängt, gilt die bekannteM ^3,4-Beziehung zwischen der Anfangsviskosität und dem Molekulargewicht.Der reziproke Wert der Komplianz (Nachgiebigkeit) hängt fast nicht von dem Molekulargewicht oberhalb eines kritischen Wertes ab, aber das scheint durch den Typ der polymeren Substanz, wie Polymolekularität oder durch den Verzweigungsgrad, beeinflußt zu sein.

     

Extraordinarily large swelling energy of iodine‐treated poly(vinyl alcohol) demonstrated by jump of a film

Organic material characteristics of volume change and stress generation have attracted the attention of many researchers aiming to develop chemomechanical systems such as artificial muscles and polymer engines having the advantages of high energy density and silent operation. Although polymer gels offer a relatively large actuator stroke, their mechanical properties are relatively poor and the working temperature is relatively low, often limited by the evaporation of liquid if contained. We have developed an iodine‐treated poly(vinyl alcohol) having extraordinarily large vapor‐induced deswelling stress reaching 59 MPa, which is one to two orders of magnitude greater than those of ordinary polymer gels. Furthermore, this material has extremely large volumetric and gravimetric energy densities reaching 1.3 × 10⁶ J m^?3 and 9.6 × 10² J kg^?1, respectively, and an elastic modulus of a few GPa and is heat‐resistant to at least 200 °C. The high performance of this material can be demonstrated by a jump of a film. © 2014 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1357–1365     

Well-defined fluorescent particles of ZnS:Cu. 1. Preparation and effects of annealing

As an application of the gel-sol procedure for the synthesis of monodispersed particles in large quantities, uniform particles of ZnS:Cu were prepared by different methods from concentrated Zn-chelate solutions of nitrilotriatic acid (NTA) with thioacetamide (TAA), in which the dopant copper ion was introduced as a coexisting mixed chelate with Zn-NTA (Method A), a Cu-NTA complex in a separate solution continuously added to a system of Zn-NTA and TAA (Method B), or a Cu(NO3)2 solution infiltrated into a dry powder of ZnS prepared by Method A (Method C). All powders thus prepared were annealed before the test of fluorescent properties. The main roles of annealing were to remove the grain boundaries of such particles as nonradiative recombination centers of excited electrons and holes and to achieve uniform distribution of dopants. However, the initial intraparticle distribution of the dopant, controlled by the different methods, decisively affected the fluorescent particles, even after the conversion of the polycrystalline particles to single-crystal particles by annealing.