Evaluation of polydispersity index Mw/Mn by quasielastic light scattering

1987 ◽  
Vol 52 (5) ◽  
pp. 1235-1245 ◽  
Author(s):  
Petr Štěpánek ◽  
Zdeněk Tuzar ◽  
Čestmír Koňák
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Decay Time ◽  
Sampling Time ◽  
Polydispersity Index ◽  
New Method ◽  
Molecular Weights ◽  
Quasielastic Light Scattering ◽  
Good Agreement

The response of quasielastic light scattering to the polydispersity of scattering objects has been investigated. A new method of the polydispersity index determination has been suggested, suitable for the range 1.02 ⪬ Mw/Mn ⪬ 2.0 and consisting in the measurement of the dependence of the apparent decay time on the correlator sampling time. The polydispersity index can be determined by comparing these dependences with the theoretical ones obtained using correlation curves simulated for various values of the polydispersity index, assuming lognormal and Schulz-Zimm distributions of molecular weights. The test measurements on polystyrene standards having molecular weights in the range 9 103 – 20.6 106 give polydispersity index values Mw/Mn that are in a good agreement with those given by the manufacturer. The polydispersity index for polystyrene having the molecular weight Mw = 20.6 106 thus determined was Mw/Mn = 1.35.

A simple method of estimation of the polydispersity index of narrow molecular weight distributions by using quasielastic light scattering data

1991 ◽  
Vol 56 (8) ◽  
pp. 1642-1652
Author(s):  
Jaromír Jakeš
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Least Squares Method ◽  
Relaxation Times ◽  
Polydispersity Index ◽  
Scattering Data ◽  
Simple Method ◽  
Quasielastic Light Scattering ◽  
Molecular Weight Distributions ◽  
Weight Distributions

A simple method of estimation of the polydispersity index of narrow molecular weight distributions using quasielastic light scattering data has been suggested. The method approximates the relaxation times distribution by using the Pearson V distribution and iterates its parameters by the least squares method to an experimental correlation function. For the usual unimodal molecular weight distributions the polydispersity index estimate is good (with an error up to 0.1) at a determined value up to 1.2, rough at a determined value up to 1.5, while above this value the method is virtually impracticable. If the type of the molecular weight distribution is known (Schulz-Zimm, lognormal, Pearson V), the polydispersity value thus determined can be corrected, which would extend the applicability limits of the method. it is shown that for an adequate determination of the polydispersity index the noise level ought to be about 10-4.

Measurement of the Isothermal Volume Dilation Accompanying the Unilateral Extension of Rubber

1959 ◽  
Vol 32 (2) ◽  
pp. 428-433
Author(s):  
Fred G. Hewitt ◽  
Robert L. Anthony
Keyword(s):  
Molecular Weight ◽  
Young’S Modulus ◽  
Experimental Results ◽  
Molecular Weights ◽  
Rubber Specimen ◽  
A Value ◽  
Fractional Increase ◽  
Internal Agreement ◽  
Good Agreement

Abstract The fractional increase in volume accompanying the isothermal extension of soft gum rubber was measured for four rubber samples at mean extensions of 14, 33, and 51%. The chain molecular weights Mc of the four samples were 5500, 5100, 4400, and 3000, with an estimated uncertainty of about 10% in each value of Mc. The observed fractional increase in volume ranged from 3.2×10−5 to 142×10−5, the latter value being observed for the sample of lowest chain molecular weight and at the extension of 51%. The experimental results for each sample have been represented by theoretical curves based on Gee's expression for the fractional increase in volume as a function of the sample extension. The theoretical curves exhibit good agreement with those of Gee, Stern, and Treloar. The process of fitting the theoretical curves to the experimental points constituted a determination of Young's modulus E for each rubber specimen. As a check on the experimental results, and also on the theory employed, determinations of E were also made by two additional methods, namely, from rough stess-strain curves, and from the relation E=3γρRT/Mc. With one exception, the internal agreement between the three determinations of E for the four different samples was satisfactory. The exception noted can probably be ascribed to the use of too small a value of Mc for the sample of lowest chain molecular weight.

DISSOCIATION AND SUBUNIT SIZE OF β-LIPOVITELLIN

1965 ◽  
Vol 43 (6) ◽  
pp. 661-670 ◽  
Author(s):  
W. H. Cook ◽  
R. A. Wallace
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Dissociation Constants ◽  
Dry Weight ◽  
Ph Values ◽  
Scattering Measurements ◽  
Solvent Displacement ◽  
Weight Method ◽  
Kinetics Of ◽  
Good Agreement

Dissociation of β-lipovitellin was detectable at pH 5.8 and increased linearly with pH. Light-scattering measurements at different pH values were consistent with a molecular weight of 2.27 × 105 for the subunit and twice this value for the associated form, confirming that it is a monomer–dimer system. This value for the molecular weight of the dimer is somewhat higher than previously reported (4.0 × 105) partly because a solvent displacement correction was used in estimating concentration by a dry weight method. Dissociation constants evaluated from light-scattering measurements and by ultracentrifugal separation were 22 × 10−6 and 29 × 10−6 respectively, in good agreement with provisional values already reported. Preliminary studies on the kinetics of this reaction indicate that, when the pH is altered, dissociation reaches the new equilibrium in about 0.5 minute but that reassociation requires about 50 minutes.

Solution Properties of Polybutadiene and trans-Polyisoprene Fractions

1963 ◽  
Vol 36 (2) ◽  
pp. 488-501
Author(s):  
W. Cooper ◽  
D. E. Eaves ◽  
G. Vaughan
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Benzene Solution ◽  
Second Virial Coefficient ◽  
Virial Coefficients ◽  
Γ Radiation ◽  
Branched Polymer ◽  
Butyl Lithium ◽  
Second Virial Coefficients ◽  
Molecular Weights

Abstract Linear polybutadienes, prepared with butyl lithium as catalyst, and polybutadienes branched by exposure to γ-radiation have been fractionated and the fractions examined by osmometry and light scattering. Turbidimetric second virial coefficients (A2τ) of mixed polymer fractions are virtually the same as those of the higher molecular weight components of the mixtures for most compositions. This is true both for mixtures of linear with linear and linear with branched polymer. The higher the molecular weight of the fraction, the greater the effect; the addition of 1 per cent microgel to a linear polymer reduced A2τ by a factor of three. The presence of microgel or high molecular weight branched polymer has been shown to be responsible for the very high molecular weights previously reported for polybutadienes from light scattering measurements. It is conveniently removed by shaking the solutions with calcium sulfate. Second virial coefficients obtained either by light scattering or osmometry are, within the limits of experimental error, uninfluenced by branching in the polymer. In general those factors which lead to increased branching also result in increased polydispersity, and it is the latter which results in the decrease in A2τ. The fall of the osmotic second virial coefficient (A2τ) with molecular weight is much smaller than would be calculated theoretically, and the fall in A2τ is greater than would be expected, notwithstanding the fact that for some of the fractions Mw/Mn<1.1. This indicates that A2τ is sensitive to the low molecular weight species present in the fractions, whereas the reverse must apply to A2τ. Natural or synthetic trans-polyisoprene showed analogous behavior to polybutadiene, although, owing to experimental difficulties, sharp branched fractions could not be obtained. The following viscosity-molecular weight relationships were obtained in benzene solution: [η]=1.45×10−4M0.76 for butyl lithium-catalyzed polybutadienes, and [η]=4.37×10−4M0.65 for natural and synthetic trans-polyisoprenes.

Development of Polymeric Micro/Nanostructures For Gene Delivery

2007 ◽  
Vol 1019 ◽  
Author(s):  
Dania Alyounes ◽  
Christopher Yengo ◽  
Tim Doran ◽  
Qi Lu ◽  
Kenneth Gonsalves
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Light Scattering ◽  
Binding Affinity ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Fluorescence Studies ◽  
Molecular Weights ◽  
Fluorescence Techniques ◽  
Exponential Increase

AbstractPluronic® polymers were screened for binding affinity to oligoribonucleotides (ORN) using fluorescence techniques. F127 (Mw 12600 g/mole) proved to have the strongest binding affinity. Urethane linkages were introduced into F127 and two other Pluronics, F38 (Mw 4700 g/mole) and F77 (Mw 6600 g/mole) to prepare polymers that were multiples of their respective initial molecular weights. A series of these polyurethane Pluronics were screened for binding affinity. Fluorescence studies showed a relationship between the molecular weight of the PO units and the binding affinity in the structures of the newly synthesized polyPluronics, especially in the case of F77. Light scattering confirmed the binding affinity between the ORN and F77 polymers. Particle size analysis showed an exponential increase until the critical micelle concentration. Other analogs of these polymers also studied for their binding affinity were poly(ester amines) and PINC.

Determination of Copolymer Molecular Weight

1968 ◽  
Vol 41 (1) ◽  
pp. 245-253 ◽  
Author(s):  
Paul Rempp ◽  
Henri Benoit
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Density Gradient ◽  
Compositional Heterogeneity ◽  
Precise Information ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Binary Copolymers

Abstract From this brief review it appears that determinations of molecular weight averages, of molecular weight distributions, and of compositional inhomogeneity of binary copolymers, require care in the choice of techniques and methods. Some of the most commonly used techniques for molecular weight determinations on homopolymers of various kinds are inadequate for the same determinations on copolymers. Others are more sensitive to fluctuations in composition than in molecular weights. Osmotic methods are the only one which are really insensitive to inhomogeneity, and which yield molecular weights. Ultracentrifugation in a density gradient yields precise information only on fluctuations in composition. Viscosity determinations require calibration, but even so, they may lead to erroneous values of the molecular weight in the case of copolymers. GPC is less sensitive to compositional heterogeneity, but cannot be applied for nonlinear copolymers. Finally, light scattering is a very powerful tool for studies on copolymers, since it leads to molecular weight averages and its helps characterize polydispersity and fluctuations in composition.

Dissociation of Phenolic Groups in Kraft Lignin at Elevated Temperatures

Holzforschung ◽  
2000 ◽  
Vol 54 (5) ◽  
pp. 519-527 ◽  
Author(s):  
Magnus Norgren ◽  
Birger Lindström
Keyword(s):  
Molecular Weight ◽  
Elevated Temperatures ◽  
Kraft Lignin ◽  
Degree Of Dissociation ◽  
Molecular Weights ◽  
Kraft Process ◽  
Poisson Boltzmann ◽  
Dissociation Curves ◽  
Complete Dissociation ◽  
Good Agreement

Summary The dissociation of the phenolic groups in a polydisperse, low molecular weight kraft lignin (Indulin AT) was studied in alkaline aqueous solutions in the temperature interval 21–70 °C, using a UV-spectrophotometric method. It was found that at a constant concentration of hydroxide ions, the degree of dissociation was decreasing when the temperature was elevated. Dissociation curves and apparent pΚ 0 values were also calculated for the polydisperse sample at the same conditions, using the van't Hoff and the Poisson-Boltzmann equations. At degrees of dissociation exceeding α ≈ 0.4, the outcome of the theoretical approach showed to be in good agreement with the experimentally obtained results. Furthermore, calculations were performed for different molecular weights of kraft lignin and from this it was found that the apparent pΚ 0 is shifted to higher values by increasing molecular weight, due to an increased electrostatic attraction of the hydrogen ions, which is arising from a less curved surface. Predictions of the dissociation behavior at temperatures reached in the kraft process were performed and under these conditions, higher molecular weight lignin fragments seem never to reach the point of complete dissociation. It was also found that an increase in temperature results in phase separation in kraft lignin solutions with high ionic strengths and pH values close to the pΚ a of the phenolic groups.

LIGHT-SCATTERING STUDIES OF SODIUM THYMONUCLEATE

1950 ◽  
Vol 28b (3) ◽  
pp. 96-104 ◽  
Author(s):  
D. B. Smith ◽  
H. Sheffer
Keyword(s):  
Hydrogen Peroxide ◽  
Molecular Weight ◽  
Light Scattering ◽  
Sodium Chloride ◽  
Aqueous Solutions ◽  
Salt Solution ◽  
Molecular Weights ◽  
Three Samples ◽  
Two Samples ◽  
Viscous Solution

The scattering of light by aqueous solutions of three different samples of sodium thymonucleate has been investigated. It was found that one sample in water consisted of randomly coiled molecules of molecular weight greater than 24 × 106. A second sample gave a less viscous solution in water and was only partially coiled, the coiling of the molecules being increased by the addition of a small amount of sodium chloride. In dilute salt solution the molecular weights of all three samples were greater than 3.7 × 106. Two samples of nucleate were degraded in solution by irradiation with ultraviolet light in the presence of hydrogen peroxide. In both cases the nucleate was converted into material consisting of rodlike molecules, 2400 Å in length and having a molecular weight of 750,000.

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