Effect of Molecular-Weight Distribution on Physical Properties of Natural and Synthetic Polymers

1948 ◽  
Vol 21 (3) ◽  
pp. 654-666 ◽  
Author(s):  
B. L. Johnson
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Synthetic Polymers ◽  
Natural Polymers ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Styrene Copolymers ◽  
Weight Distributions

Abstract The molecular weights of rubberlike polymers are average values for mixtures of macromolecules which differ greatly in size. The heterogeneity of natural rubber was recognized as early as 1929 by Whitby. The fact that solutions of higher quality crude rubbers are more viscous than lower quality rubbers was observed by Axelrod in 1905. Other workers have separated rubber solutions into fractions of differing molecular weight and have studied the properties of the fractions. In the case of synthetic polymers, these heterogeneous mixtures of molecules have been characterized by fractional precipitation and construction of molecular-weight distribution curves. The particular type of distribution determined in this investigation is that obtained from weight average properties based on viscosity measurements of fractions of the polymers. Application of these methods to the characterization of natural polymers confirmed observations that a variety of molecular-weight distributions existed in the case of the natural polymers. The physical properties of the natural polymers having these diverse molecular-weight distributions were well known. Therefore a correlation of their physical properties and weight distributions seemed pertinent to an evaluation of the fractionation technique. Such a correlation had not been possible on early butadiene-styrene copolymers because of the similarity of the distributions then obtained, even under different polymerization conditions.

Controlling Molecular Weight Distributions Through the Mixing of Low Dispersity Polymer Samples: A Predictive Framework

2019 ◽  
Author(s):  
Maarten Rubens ◽  
Tanja Junkers
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Radical Polymerizations ◽  
Systematic Framework

<div>The physical properties of polymer samples are dependent on the overall shape and breadth of the molecular weight distribution (MWD). A small number of methods are available to tune the shape and characteristics of MWDs based on influencing controlled radical polymerizations and on mixing of individual distributions. However, no systematic framework exists to date to predict the characteristics and shapes of artificial MWDs prior the experiments. In this work we present such framework based on interpolation of individual distributions.</div>

Molecular Weight Distributions of Elastomers—Comparison of Gel Permeation Chromatography with Other Techniques

1965 ◽  
Vol 38 (4) ◽  
pp. 823-831 ◽  
Author(s):  
Leon W. Gamble ◽  
Lowell Westerman ◽  
Ebnest A. Knipp
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Gel Permeation Chromatography ◽  
Molecular Weights ◽  
The Past ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Gel Permeation ◽  
Polymer Fractionation

Abstract During the past decade interest in polymer fractionation for evaluating molecular weight distribution has increased. New polymers, such as polypropylene, high density polyethylene and many others have been subjected to extensive characterization, but some older polymers, including natural rubber have not. In recent years column fractionation has received a great deal of attention; a review has been made by Schneider. Most of the techniques of polymer fractionation, such as precipitation from solution and column fractionation, are quite lengthy and require days or even weeks to complete. A more rapid method for molecular weight distribution has been the goal of polymer chemists for years. The most promising of the rapid methods are turbidimetric and gel permeation chromatography by which analysis is accomplished in a few hours. This paper discusses application of gel permeation chromatography to fractionation of elastomers. In addition this technique is compared with data from column fractionation, light scattering and osmometry. Some of the assumed factors used in converting gel permeation data into molecular weights are in error. But by calibration of the gel permeation chromatograph with classical methods reliable data can be obtained.

Controlling Molecular Weight Distributions Through the Mixing of Low Dispersity Polymer Samples: A Predictive Framework

2019 ◽  
Author(s):  
Maarten Rubens ◽  
Tanja Junkers
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Radical Polymerizations ◽  
Systematic Framework

<div>The physical properties of polymer samples are dependent on the overall shape and breadth of the molecular weight distribution (MWD). A small number of methods are available to tune the shape and characteristics of MWDs based on influencing controlled radical polymerizations and on mixing of individual distributions. However, no systematic framework exists to date to predict the characteristics and shapes of artificial MWDs prior the experiments. In this work we present such framework based on interpolation of individual distributions.</div>

The Investigation of Molecular-Weight Distribution in Rubberlike Polymers

1957 ◽  
Vol 30 (2) ◽  
pp. 507-527 ◽  
Author(s):  
S. E. Bresler ◽  
I. Y. Poddubnyĭ ◽  
S. Y. Frenkel
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymerization Reaction ◽  
Continuous Series ◽  
Gaussian Shape ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Asymmetric Shape

Abstract In an investigation of three different synthetic rubbers, methods of fractionation were examined and measurements were made of the molecular-weight distribution by analysis of fractions. The following conclusions may be drawn. (1) The method of equivalent Gaussian distributions correctly reproduces the distribution within each fraction and makes it possible to distinguish the broadening of the sedimentation curve attributable to diffusion and that attributable to polydispersion. (2) The method of accounting for the final concentration of the solution under investigation introduced by us result in correct values of molecular weights of fractions and correct values of standard deviations. (3) Comparison of a series (about 10) of fractions of a given polymer makes it possible to transpose the sedimentation constant distributions into the distribution of molecular weights in a simple and natural way. An investigation of the three rubbers demonstrates two facts. (1) Fractionation of rubbers by precipitation from solutions gives true fractions, i.e., mode values of molecular weights and sedimentation constants do not overlap but form continuous series. By this means fractionation of K-1 and K-3 resulted in very homogeneous fractions of Gaussian shape having dispersion coefficients smaller than 0.33. Fractionation of K-2 resulted in less homogeneous fractions of somewhat asymmetric shape; however, in this case, the broadness and asymmetry of fractions, as it is easy to show, does not exceed the limits predicted by the theory of fractionation. (2) The method of determination of molecular-weight distributions by tracing the steplike curve of precipitation, with subsequent smoothing by graphic differentiation, gives a correct picture of the distribution function of polymers for molecular weights; however, the finer details of distribution can be distorted and lost in tracing the steplike curve. The molecular-weight distributions of synthetic rubbers by the ultracentrifuge method must be closely related to the process of genesis of a polymer, i.e., with the mechanism of the polymerization reaction. Thus, with proper experimental technique our method can be applied to the investigation of various mechanisms of polymerization and polycondensation.

Characterization of Elution Chromatography Fractions from CIS-Polybutadiene by GPC

1970 ◽  
Vol 43 (6) ◽  
pp. 1439-1450 ◽  
Author(s):  
W. V. Smith ◽  
S. Thiruvengada
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Low Molecular Weight ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Log Normal ◽  
Analytical Fractionation ◽  
Molecular Weight Fractions ◽  
Elution Chromatography

Abstract A preparative fractionation of about 23 g of a commercial cis-polybutadiene rubber is described. The method employed was a solvent elution chromatographic method with very little temperature gradient. The molecular weight distributions of the fractions obtained were determined by an analytical fractionation of 20 mg of polymer. The method was similar to the preparative fractionation and involved solvent elution chromatography. The fractions obtained were assayed for quantity, molecular weight, and molecular weight distribution by GPC. The low molecular weight fractions of the preparative fractionation had molecular weight distributions which could be closely approximated by two log normal distributions, the low molecular weight component having the narrower width. The ratio of weight to number average molecular weight was found to be about 1.1 for these samples. The higher molecular weight fractions could also be approximated by two log normal distributions; however, in these fractions the low molecular weight component had a very broad distribution but constituted only a small portion of the sample. The widths of the GPC curves of the fractions correlate satisfactorily with the molecular weight distributions found by the analytical refractionations. The GPC width is a sensitive criterion of the width of the molecular weight distribution even when only two columns are used. It is felt that the analytical fractionation procedure presented gives more detailed information on the molecular weight distribution than is easily obtainable from an ordinary GPC curve.

Simple and secure data encryption via molecular weight distribution fingerprints

2020 ◽  
Vol 11 (40) ◽  
pp. 6463-6470
Author(s):  
Jeroen H. Vrijsen ◽  
Maarten Rubens ◽  
Tanja Junkers
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Data Encryption ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Secure Data

A method for encryption and safe transmission of data in the shape of molecular weight distributions (MWD) is presented.

Fractionation of Polymers

1972 ◽  
Vol 45 (3) ◽  
pp. 667-708 ◽  
Author(s):  
W. V. Smith
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Structural Information ◽  
Gel Permeation Chromatography ◽  
Molecular Weight Distributions ◽  
Polymer Solubility ◽  
Homogeneous Composition ◽  
Layer Chromatography

Abstract Fractionation is an important tool for obtaining structural information on polymers. It is also important for isolating relatively homogeneous samples of polymer to use in determining relationships between structure and properties. The most common structural information obtained from fractionation is molecular weight distribution (MWD). This is a very important factor in determining processing behavior. To a lesser extent MWD affects the properties of finished polymer products. It is quite important in helping to elucidate mechanisms of polymer formation. Development of gel permeation chromatography (GPC) over the past few years has provided a fast convenient tool for comparing molecular weight distributions. GPC is fast enough that it may even be considered as a potential means of controlling polymerization processes. The chemical composition of copolymers can be determined using fractionation techniques. For this the fractionations based on polymer solubility are particularly suitable. Thin layer chromatography also shows promise in this area. This information is of importance in respect to some physical properties such as solvent and oil resistance and crystallinity. It is also useful in elucidating mechanisms of polymerization. While the ultracentrifuge has not been used extensively in the investigation of industrial polymers, it does have the advantage of being capable of providing absolute moleclar weight information. When it is desired to establish relationships between the structure of polymers and their physical properties it is always desirable to work with polymers having a narrow molecular weight distribution and a homogeneous composition. This can frequently best be accomplished by using fractionated polymer samples. At the present time fractionations based on solubility are the principal ones used through preparative fractionations based on GPC are now possible and a limited amount of literature in this area is now appearing.

Synthesis and Properties of Uniform Polyisoprene Networks. I. Synthesis and Characterization of α,ω-Dihydroxy-Polyisoprene

1976 ◽  
Vol 49 (2) ◽  
pp. 303-319 ◽  
Author(s):  
M. Morton ◽  
L. J. Fetters ◽  
J. Inomata ◽  
D. C. Rubio ◽  
R. N. Young
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Soluble Fraction ◽  
Synthesis And Characterization ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
The Subject

Abstract The results of this study are the first to show that high-1,4 linear α,ω-dihydroxypolydienes can be synthesized with (a) predictable molecular weights, (b) narrow molecular weight distributions, and (c) high functionalities. Using the functionalized polyisoprenes prepared in this work, a series of networks was prepared with a purified triisocyanate as the chain linking agent. The soluble fraction in these networks ranged from 4.6 to 1.6 per cent. The characteristics and physical properties of these networks will be the subject of a forthcoming publication.

Effect of Molecular Weight Distribution of Mineral Oil on Tribofailure of Spur Gears

1981 ◽  
Vol 103 (1) ◽  
pp. 210-218 ◽  
Author(s):  
F. Hirano ◽  
K. Ichimaru ◽  
K. Kinoshita ◽  
T. Sakai
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Film Formation ◽  
Spur Gears ◽  
Mineral Oils ◽  
Mild Conditions ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Failure Loads

Using a series of straight mineral oils with a variety of molecular weight distributions failure loads of spur gears with gear ratios 27:25 and 1:1 were investigated. The failure loads in the case of the synchronous engagement 1:1 were considerably higher than those in the asynchronous engagement 27:25 as a result of imprinting of asperities of harder teeth on softer engaged teeth. The correlation among the results was found to be quite regular, showing the beneficial effect of wide-ranged oils in the molecular weight distribution. Summarizing the obtained results, it is concluded that the failure loads of narrow-ranged oils were conditioned by their viscosity grades, and that those of wide-ranged oils increased further with the aid of oxide film formation on teeth. Results of four-ball tests and two-disk tests previously carried out under mild conditions using the same narrow-ranged and wide-ranged oils show the similar feature to those of the gear tests.

Molecular Weight Dependence of Relaxation Spectra of Amorphous Polymers in the Rubbery Region. VIII. Comparisons of Experimental Relaxation Spectra of Commercial Synthetic Rubbers with those Estimated from Molecular Weight Distributions

1967 ◽  
Vol 40 (2) ◽  
pp. 484-492 ◽  
Author(s):  
Genichi Yasuda
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Mechanical Relaxation ◽  
General Validity ◽  
Relaxation Spectra ◽  
Molecular Weight Distributions ◽  
Synthetic Rubber ◽  
Weight Distributions

Abstract Synthetic rubber of different species, types, and degrees of mastication were used to examine the general validity of the proposed relationship between mechanical relaxation spectra in the rubbery region and molecular weight distribution. Results show that the proposed relationship can be well used to discuss quantitatively the role of molecular weight distribution in the theoretical behavior of a raw rubber while being processed.

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