Search results for "Molar mass distribution"
showing 10 items of 115 documents
1972
Different rates of initiation and propagation, e.g., in the case of living polymerization, lead to considerable deviations from a POISSON distribution. Using a bifunctional initiator the distribution obtained is composed of a single distribution and a coupled distribution. The maximum value of xw/xn never exceeds 1.4 even for a ratio kp/ki = 106. Verschiedene Start- und Wachstumsgeschwindigkeiten fuhren z. B. im Fall der lebenden Polymerisation zu erheblichen Abweichungen von einer POISSON-Verteilung. Die Verwendung eines bifunktionellen Initiators ergibt eine Verteilung, die sich aus einer einfachen und einer gekoppelten Verteilung zusammensetzt. Der Wert xw/xn uberschreitet nicht den Betr…
Die Bestimmung der Molekulargewichtsverteilung von nichtkristallisierenden Polymeren mit dem Elektronenmikroskop, 5. Bestimmung der Masse der Einzelm…
1977
A method is described for the determination of the molecular weight distribution (MWD) of various polymers from electron microscopy pictures of their molecules. It is shown, that the number of molecules needed to construct the distribution is between 200 and 300. Furthermore, with macroscopic density of the polymer and the volume determined by electron microscopy, the correct mass of a single molecule is obtained. The method is demonstrated for samples of polystyrene and poly(methyl methacrylate) and the results are compared with those of GPC-measurements.
(Co)polymerisation Behaviour of Supported Metallocene Catalysts: Carrier Effect
2006
The polymerisation and copolymerisation of ethylene with 1-hexene over metallocene catalysts L 2 ZrCl 2 / MAO (L = Cp, n-BuCp, t-BuCp, i-PrCp, Me 5 Cp) supported on different types of carriers (MgCl 2 (MeOH) 6 or silica with CH 3 surface groups obtained in the sol-gel process) were studied. It was demonstrated that both the metallocene structure and the type of inorganic support affected catalyst activity and polymer properties such as melting point, molecular weight and molecular weight distribution. The metallocene structure also determined comonomer incorporation, both for homogeneous and supported catalytic systems. When a catalyst is anchored on a support, it becomes less effective at …
1976
A radical mechanism is proposed for the formation of the 1,2-polymer 2 in the “spontaneous” polymerization of 4-vinylpyridinium salts 4-VP.HX (X=NO3, ClO4, HSO4, I) in aqueous solution on the basis of strong inhibition by oxygen and other radical inhibitors. Quantitative investigation of the influence of oxygen on the formation of the 1,2-polymer allowed the derivation of a formal kinetic scheme for the initiation and polymerization steps which is consistent with a free radical mechanism. Dependence of the average molecular weight of 2 on monomer concentration is in agreement with this model. Dependence of the inhibition time on the oxygen concentration as well as an acceleration of the fin…
Kristallisation und schmelzverhalten von fraktionen verzweigten polyethylens, 1. Darstellung und charakterisierung der fraktionen
1983
A branched polyethylene with broad molecular weight distribution was separated into a series of fractions by fractional precipitation from dilute solution. The fractions were characterized by viscometric and density measurements, IR-spectroscopy and calorimetry. The methyl group content and the density turned out as largely constant. Molecular weight effects show up in the melting behaviour. The main range of melting and the end of the melting curve shift to lower temperatures with decreasing molecular weight. Compared to the overall extension of the melting range these shifts are small. One has to conclude that polydispersity gives only a minor contribution to the broadening of the melting…
Kinetik und Molekulargewichtsverteilung eines anionischen Polymerisationsprozesses mit momentanem Start bei simultanem Monomerabbruch
1973
Die Kinetik und die Molekulargewichtsverteilung wird fur einen anionischen Polymerisationsprozes mit einem momentanen Startschritt und mit simultanem Monomerabbruch berechnet. Ein derartiger Polymerisationsablauf ist bei der anionischen Polymerisation von Methylmethacrylat in polaren Losungsmitteln zu erwarten. — Die Molekulargewichtsverteilung geht mit steigendem Monomerabbruch in eine SCHULZ-FLORY-Verteilung uber. The kinetics and the molecular weight distribution are calculated for an anionic polymerization with rapid initiation and simultaneous deactivation by the monomer. Such a process is to be expected for the anionic polymerization of methylmethacrylate in polar solvents. — The mole…
Influence of molecular parameters on the elongational behaviour of different polyethylenes and their blends
1988
Elongational data on a large number of polyethylene samples with different structures and their blends are presented in order to evaluate the influence of the molecular weight and molecular weight distribution for a given degree of long chain branching. The elongational viscosity rises with the number of branch points and also with molecular weight and molecular weight distribution. Simple relationships between elongational viscosity at a given deformation and molecular parameters are presented.
1995
45 g of poly(acrylic acid) (PAA 500) with a trimodal molar mass distribution (Mw = 500 kg/mol, (Mw/Mn) −1 = 2.33) were fractionated by means of CPF (continuous polymer fractionation) in two steps using 1,4-dioxane as solvent. The counter-current extraction was performed in a glass column (length: 190 cm, diameter: 1.5 cm) filled with a network of wires, introducing the feed 75 cm from its upper end. The distribution of the highest molar mass fraction (Mw = 760 kg/mol) is unimodal and comparatively narrow ((Mw/Mn) −1 = 0.66). Indications exits that fractionation is not only taking place with respect to molar mass but also with respect to tacticity. Mit Hilfe der kontinuierlichen Polymerfrakt…
Anionische Polymerisation in Schwach Solvatisierenden Lösungsmitteln
2007
The anionic polymerization of styrene initiated by cumylsodium and carried out in cumyl methyl ether has been examined with use of conversion kinetics and molecular weight distribution. The solvent has a weaker solvation power than THF and THP, which have been studied with the same experimental technique. The polymerization rate is first order relative to monomer and the rate constant has a value of ca. 1 mole−1 1. sec.−1 at − 20.5°C. The constant is only slightly dependent on the initiator concentration, but the molecular weight distribution is broader than a Poisson function. Added electrolyte has little effect on the propagation constant but it greatly alters the molecular weight distrib…
Bestimmung der molekularen konstanten von naturkautschuk III. Molekulargewicht trägheitsradius und thermodynamische eigenschaften von cyclohexan-kaut…
1960
Lichtstreuungsmessungen an Crepekautschuk in Cyclohexan ergeben Mw = 1,85·106. In Verbindung mit Diffusions- und Sedimentationsmessungen ergibt sich als wahrscheinlichster Wert Mw = 1,7·10−6. Unter Verwendung der Messungen von CARTER, SCOTT und MAGAT wird als Molekulargewichts-Viskositatsbeziehung die Gleichung fur Losungen von Naturkautschuk in Cyclohexan vorgeschlagen. Der 2. Virialkoeffizient und der STAUDINGER-Index nehmen in der Reihenfolge Benzol, Cyclohexen, Cyclohexan zu. Die beiden ersten Losungsmittel sind endotherm, Cyclohexan ist exotherm. Der Tragheitsradius der Molekulknael nach Lichtstreuungsmessungen ist etwa Rw = 1000 A. Der wahrscheinlichste Wert unter Mitberucksichtigung …