Search results for "Radius of gyration"
showing 10 items of 83 documents
Synthesis and solution properties of star-shaped poly(tert-butyl acrylate)
2000
A series of star polymers consisting of poly(tert-butyl acrylate) arms and an ethyleneglycol dimethacrylate (EGDMA) microgel core were synthesized using anionic polymerization. The effect of various parameters (precursor length, ratio [[EGDMA]/[Initiator], reaction time, and overall concentrations) on the average number of arms was investigated. Molecular weights were determined using GPC coupled with an online viscometer and MALLS. The exponents for the relation between intrinsic viscosity or radius of gyration and molecular weight, respectively, are extremely low, indicating that the dimensions of the star polymers only slightly increase with the number of arms. After a certain number of …
Static and Dynamic Properties of a n-C100H202 Melt from Molecular Dynamics Simulations
1997
We present in this work results from atomistic molecular dynamics simulations of a n-C100H202 melt. This work represents a first effort to simulate a fully equilibrated ensemble of chains of suffic...
Über die verzweigung von polydodecylmethacrylat
1970
Zur Untersuchung der Losungseigenschaften und des Ausmases der Verzweigung von radikalisch gewonnenem Polydodecylmethacrylat wurden Fraktionen von niedrig- und hochumgesetzten Praparaten im Molekulargewichtsbereich von 1,5·105 bis 8·106 auf ihr Molekulargewicht und ihre Knaueldimension hin vermessen. Die Methoden der Lichtstreuung, der Viskosimetrie, der Sedimentation in der Ultrazentrifuge, der Osmometrie und der Gelchromatographie wurden benutzt. Fur die Streulichtmessungen diente ein Eigenbaulichtstreuungsgerat, das wegen seines grosen Winkelmesbereiches eine recht genaue Festlegung der Anfangssteigung der Streukurve und damit des Tragheitsradius ermoglicht. Das Quadrat des Tragheitsradi…
Untersuchungen über das Reibungsverhalten von Polymethacrylsäuremethylestern in verschiedenen Lösungsmitteln
1963
An drei Polymethacrylsauremethylester-Fraktionen wurden Sedimentationskoeffizienten, Diffusionskoeffizienten und Viskositatszahlen im Θ-Losungsmittel n-Butylchlorid und in den guten Losungsmitteln Aceton und Dioxan gemessen. Die Reibungszahl [f] = kT/Dη0 ist der Ausdehnung des Knauels proportional. Mit dem Tragheitsradius R gilt [f] = Ψ·R, worin der Faktor Ψ von der Gute des Losungsmittels abhangt. Experimentell wurde am Θ-Punkt ΨΘ = 15,5 gefunden. Hydrodynamische Rechnungen verschiedener Autoren ergeben dagegen ΨΘ = 12,5. In den beiden guten Losungsmitteln fanden wir Ψ ≈ 13. Fur alle Losungsmittel last sich Ψ als Funktion des Exponenten a der Viskositats-Molekulargewichtsbeziehung [η] = Kη…
Three-step decay of time correlations at polymer-solid interfaces
2012
Two-step decay of relaxation functions, i.e., time scale separation between microscopic dynamics and structural relaxation, is the defining signature of the structural glass transition. We show that for glass-forming polymer melts at an attractive surface slow desorption kinetics introduces an additional time scale separation among the relaxational degrees of freedom leading to a three-step decay. The inherent length scale of this process is the radius of gyration in contrast to the segmental scale governing the glass transition. We show how the three-step decay can be observed in incoherent scattering experiments and discuss its relevance for the glass transition of confined polymers by an…
The Allosteric Effector l-Lactate Induces a Conformational Change of 2×6-meric Lobster Hemocyanin in the Oxy State as Revealed by Small Angle X-ray S…
2001
Abstract Hemocyanins are multisubunit respiratory proteins found in many invertebrates. They bind oxygen highly cooperatively. However, not much is known about the structural basis of this behavior. We studied the influence of the physiological allosteric effectorl-lactate on the oxygenated quaternary structure of the 2×6-meric hemocyanin from the lobster Homarus americanus employing small angle x-ray scattering (SAXS). The presence of 20 mm l-lactate resulted in different scattering curves compared with those obtained in the absence of l-lactate. The distance distribution functionsp(r) indicated a more compact molecule in presence ofl-lactate, which is also reflected in a reduction of the …
On the equation of state for thermal polymer solutions and melts with attractive interaction
1996
We perform Monte Carlo simulations of a lattice model for polymer melts, i. e., the bond fluctuation model in three dimensions. By using an energy parameter that prefers relatively long bonds, the model exhibits a glass transition at low temperatures, in close qualitative similarity to experiment. We modify this model by adding an attractive interaction of variable strength. We demonstrate that a small interaction strength has only a very small effect on the static properties of the melt. For a fixed strength of the potential, the chemical potential is measured by a modified particle-insertion method over a large range of temperatures and densities. The osmotic pressure is obtained by therm…
Solution behavior of 4-arm poly(tert-butyl acrylate) star polymers
2010
Abstract This paper reports the synthesis of 4-arm poly( tert -butyl acrylate) stars of different molar masses up to 10 6 g/mol by the “core-first” method using ATRP. All obtained stars have a monomodal and narrow molar-mass distribution ( The dilute-solution properties of these star polymers were investigated in good solvents (tetrahydrofuran and acetone). Gel permeation chromatography and dynamic and static light scattering were used to measure the hydrodynamic properties including intrinsic viscosity [ η ], radius of gyration R g , hydrodynamic radius R h , second virial coefficient A 2 and diffusion coefficient D 0 . These data were used to establish relationships between these paramet…
Topologically Controlled Interpolyelectrolyte Complexes
2008
The complexation of a cylindrical polyelectrolyte−brush−surfactant complex (PMMPSS−C12) and an oppositely, highly charged cylindrical polyelectrolyte−brush (PMMPEI−PEO) in dimethylformamide (DMF) l...
Unusual finite size effects in the Monte Carlo simulation of microphase formation of block copolymer melts
1995
Extensive Monte Carlo simulations are presented for the Fried-Binder model of block copolymer melts, where polymer chains are represented as self and mutually avoiding walks on a simple cubic lattice, and monomer units of different kind (A, B) repel each other if they are nearest neighbors (e AB > O). Choosing a chain length N = 20, vacancy concentration Φ v = 0,2, composition f = 3/4, and a L × L × L geometry with periodic boundary conditions and 8 ≤ L ≤ 32, finite size effects on the collective structure factor S(q) and the gyration radii are investigated. It is shown that already above the microphase separation transition, namely when the correlation length ζ(T) of concentration fluctuat…