The effect of molecular weight distribution on the physical properties of polystyrene

1959 ◽  
Vol 39 (135) ◽  
pp. 87-100 ◽  
Author(s):  
Herbert W. McCormick ◽  
Frank M. Brower ◽  
Leo Kin
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution

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.

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>

Synthesis and Dilute-Solution Behavior of Model Star-Branched Polymers

1978 ◽  
Vol 51 (3) ◽  
pp. 406-436 ◽  
Author(s):  
B. J. Bauer ◽  
L. J. Fetters
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Melt Processing ◽  
Branched Polymers ◽  
Linear Polymers ◽  
Dilute Solution ◽  
Long Chain

Abstract The occurrence of polymers branched in a random fashion is common. Chain transfer reactions can cause short- and long-chain branching in polymerizations such as the high-pressure polymerization of ethylene. Branching can also be introduced intentionally by the use of a polyfunctional monomer in end-linking polymerizations. Similar branching can be produced in addition polymerizations by the use of a small amount of difunctional monomer, e.g., divinylbenzene. There also has been much interest in graft polymerization by which long chain branches can be introduced onto a backbone, which is often a different polymer from the branches. The properties of branched polymers can be quite different from those of linear polymers of the same molecular weight. For example, bulk viscosities as well as concentrated and dilute solution viscosities can be lower for branched polymers than for a linear material of equivalent molecular weight. As an example, the melt processing behavior of polymers can be manipulated by alterations in the average molecular weight, molecular weight distribution, and the frequency and length of long branches in the molecules. Thus, there is an obvious need to correlate and characterize the type and degree of branching in a polymer with its effect on the physical properties in solution or melt. In all of the above examples of branching, there is a mixture of branched and unbranched material. The unbranched and branched polymers can have a wide molecular weight distribution, as can the branches themselves. Also, the frequency of branches and the segment lengths between branch points can vary. Hence, the physical properties of such materials represent an average of the properties of all the different species present.

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>

Technological Characteristics of Polyisoprenes with Different 1,4-cis Contents

1966 ◽  
Vol 39 (5) ◽  
pp. 1593-1607 ◽  
Author(s):  
M. Bruzzone ◽  
G. Corradini ◽  
F. Amato
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Crosslink Density ◽  
Physical Property ◽  
Density Range ◽  
Catalytic Systems ◽  
Crosslink Densities ◽  
Natural And Synthetic

Abstract This work deals with the physical properties of polyisoprenes with different cis content. Small changes in the structural purity of these polymers affect strongly their crystallizability and, consequently, influence cured elastomer properties. In order to evaluate quantitatively the influence of cis content on elastomer properties it is clearly not sufficient to compare properties of the natural and synthetic polymers, obtained with different catalytic systems, relying on the same curing recipe. The difference in vulcanization kinetics, molecular weight distributions, dispersion of the ingredients in the elastomer, and other minor variables can in fact overshadow the influence of cis content on properties of the final product. In order to achieve a clear distinction between the effect of cis content and the influence of other variables, we decided to compare physical properties of vulcanized products over a large range of crosslink densities, obtained with suitable changes of the curing system, allowing for three variables: sulfur, accelerator, and curing time. The accelerator is a sulfenamide, suitable both for natural and synthetic polyisoprenes. When all the results obtained with different curing systems and times are plotted on a single diagram, in terms of physical property against crosslink density (or modulus) substantial differences between different polyisoprenes are noticed. In the low crosslink density range properties are probably influenced by network flaws related to the elastomer molecular weight distribution. Beyond a certain limit of crosslink densities the effect of molecular weight distribution decreases as the network flaws, mainly due to the ends of the primary chains, become less and less important. In this crosslink density range, properties are related mainly to structural purity, which influences the crystallizability of the network chains and perhaps also the nature of the inter or intramolecular bonds formed by curing.

The molecular weight distribution problem and reptation mixing rules

2000 ◽  
Vol 42 (1) ◽  
pp. 26-40 ◽  
Author(s):  
R. S. Anderssen ◽  
M. Westcott
Keyword(s):  
Molecular Weight ◽  
Physical Properties ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Practical Importance ◽  
Relaxation Modulus ◽  
Polymer Dynamics ◽  
Mixing Rules ◽  
Molecular Weights ◽  
Double Reptation

AbstractMixing rules model how the physical properties of a polymer, such as its relaxation modulus G(t), depend on the distribution w(m) of its molecular weights m. They are of practical importance because, among other things, they allow estimates of the molecular weight distribution (MWD) w(m) of a polymer to be determined from measurements of its physical properties including the relaxation modulus. The two most common mixing rules are “single” and “double” reptation. Various derivations for these rules have been published. In this paper, a conditional probability formulation is given which identifies that the fundamental essence of “double” reptation is the discrete binary nature of the “entanglements”, which are assumed to occur in the corresponding topological model of the underlying polymer dynamics. In addition, various methods for determining the MWD are reviewed, and the computation of linear functionals of the MWD motivated and briefly examined.

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