An Investigation of the Molecular Weight Distribution of Polymers with the Aid of the Ultracentrifuge

1957 ◽  
Vol 30 (2) ◽  
pp. 487-506
Author(s):  
S. E. Bresler ◽  
S. Y. Frenkel
Keyword(s):  
Molecular Weight ◽  
Distribution Function ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Functional Relation ◽  
Distribution Functions ◽  
Linear Polymers ◽  
Molecular Weights ◽  
Direct Experiment ◽  
And Diffusion

Abstract In the present paper a method for studying the molecular weight distribution of linear polymers, involving the following stages, is developed: 1. Fractionation of the polymer into a series of sufficiently narrow fractions and investigation of these fractions with the aid of the ultracentrifuge and diffusion. 2. Plotting the distribution functions of sedimentation constants for each fraction and subsequent summation of curves in order to build up the distribution function of the sedimentation constants for the whole polymer. 3. Discovery of a general functional relation between the sedimentation constants and molecular weights for a given series of polymer homologs and construction of the distribution function of molecular weights of the polymer. The basis of the method developed by us (method of equivalent Gaussian distributions) was confirmed by direct experiment. Application of this method of investigation to a number of industrial polymers will be described in the next paper.

scholarly journals A new general method for the assessment of the molecular-weight distribution of polydisperse preparations. Its application to an intestinal epithelial glycoprotein and two dextran samples, and comparison with a monodisperse glycoprotein

1973 ◽  
Vol 135 (4) ◽  
pp. 649-653 ◽  
Author(s):  
Richard A. Gibbons ◽  
Stephen N. Dixon ◽  
David H. Pocock
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Continuous Distribution ◽  
Distribution Functions ◽  
Intestinal Epithelial ◽  
Cysticercus Tenuicollis ◽  
Molecular Weights ◽  
Two Samples ◽  
General Method

A specimen of intestinal glycoprotein isolated from the pig and two samples of dextran, all of which are polydisperse (that is, the preparations may be regarded as consisting of a continuous distribution of molecular weights), have been examined in the ultracentrifuge under meniscus-depletion conditions at equilibrium. They are compared with each other and with a glycoprotein from Cysticercus tenuicollis cyst fluid which is almost monodisperse. The quantity c−⅓(c=concentration) is plotted against ξ (the reduced radius); this plot is linear when the molecular-weight distribution approximates to the ‘most probable’, i.e. when Mn:Mw:Mz: M(z+1)....... is as 1:2:3:4: etc. The use of this plot, and related procedures, to evaluate qualitatively and semi-quantitatively molecular-weight distribution functions where they can be realistically approximated to Schulz distributions is discussed. The theoretical basis is given in an Appendix.

The Molecular Weights of Rubber and Related Materials. V. The Interpretation of Molecular Weight Measurements on High Polymers

1945 ◽  
Vol 18 (1) ◽  
pp. 1-7
Author(s):  
Geoffrey Gee
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Convenient Method ◽  
Weight Distribution ◽  
Linear Structure ◽  
Linear Polymers ◽  
Viscosity Measurements ◽  
Molecular Weights ◽  
Homogeneous Linear ◽  
Weight Data

Abstract Unless an ultracentrifuge is available, absolute molecular weight determinations must be based ultimately on osmotic data. Viscosity measurements furnish a convenient method of interpolation, and give reliable results for homogeneous linear polymers. The viscosity molecular-weight of a typical unfractionated polymer would not be very seriously in error unless the polymer were extensively branched. No reliable conclusions about molecular-weight distribution can be drawn from molecular-weight data alone without carrying out a fractionation, although a useful guide to the homogeneity of a polymer known to be of linear structure is furnished by the ratio of the viscosity and osmotic molecular weights.

scholarly journals Matrix-graph model of the polymer materials destruction process

2018 ◽  
Vol 80 (3) ◽  
pp. 50-55
Author(s):  
A. A. Khvostov ◽  
S. G. Tikhomirov ◽  
I. A. Khaustov ◽  
A. A. Zhuravlev ◽  
A. V. Karmanov
Keyword(s):  
Mathematical Model ◽  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Graph Model ◽  
Polymer Materials ◽  
Simulation Environment ◽  
Destruction Process ◽  
Molecular Weights ◽  
The Mathematical Model

The paper deals with the problem of mathematical modeling of the process of thermochemical destruction using the theory of graphs. To synthesize a mathematical model, the Markov chain is used. For the formalization of the model a matrix-graph method of coding is used. It is proposed to consider the process of destruction as a random process, under which the state of the system changes, characterized by the proportion of macromolecules in each fraction of the molecular mass distribution. The intensities of transitions from state to state characterize the corresponding rates of destruction processes for each fraction of the molecular weight distribution (MWD). The processes of crosslinking and polymerization in this work have been neglected, and it is accepted that there is a probability of transition from any state with a lower order index (corresponding to fractions with higher molecular weights) to any state with a higher index (corresponding fractions with lower molecular weights). A computational formula is presented for estimating the number of arcs and model parameters from a given number of fractions of the molecular weight distribution of the polymer. An example of coding in a matrix form of a graph model of the process of degradation of polybutadiene in solution for the case of six fractions of the molecular weight distribution is shown. As the simulation environment, the interactive graphical simulation environment of MathWorks Simulink is used. To evaluate the parameters of the mathematical model, experimental studies of the degradation of polybutadiene in solution were carried out. The chromatography of the polybutadiene solution was used as the initial data for the estimation of the MWD polymer. The considered matrix-graph representation of the structure of the mathematical model of the polymer destruction process makes it possible to simplify the compilation of the model and its software implementation in the case of a large number of vertices of the graph describing the process of destruction

scholarly journals Water vapor induced self-assembly of islands/honeycomb structure by secondary phase separation in polystyrene solution with bimodal molecular weight distribution

2021 ◽  
Author(s):  
Maciej Łojkowski ◽  
Adrian Chlanda ◽  
Emilia Choińska ◽  
Wojciech Swieszkowski
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Self Assembly ◽  
Secondary Phase ◽  
Honeycomb Structure ◽  
Polymer Chains ◽  
Molecular Weights ◽  
Secondary Phase Separation

<p>The formation of complex structures in thin films is of interest in many fields. Segregation of polymer chains of different molecular weights is a well-known process. However, here, polystyrene with bimodal molecular weight distribution, but no additional chemical modification was used. It was proven that at certain conditions, the phase separation occurred between two fractions of bimodal polystyrene/methyl ethyl ketone solution. The films were prepared by spin-coating, and the segregation between polystyrene phases was investigated by force spectroscopy. Next, water vapour induced secondary phase separation was investigated. The introduction of moist airflow induced the self-assembly of the lower molecular weight into islands and the heavier fraction into a honeycomb. As a result, an easy, fast, and effective method of obtaining island/honeycomb morphologies was demonstrated. The possible mechanisms of the formation of such structures were discussed.</p>

Sign in / Sign up

Export Citation Format

Share Document