Branching in Polymer Chains

1972 ◽  
Vol 45 (3) ◽  
pp. 519-545 ◽  
Author(s):  
V. A. Grechanovskii
Keyword(s):  
Molecular Weight ◽  
Breaking Strength ◽  
Strength Properties ◽  
Polymer Chains ◽  
Branched Polymers ◽  
Shear Stresses ◽  
Linear Polymers ◽  
Concentrated Solutions ◽  
Active Centers ◽  
Lower Viscosity

Abstract The branching that occurs in molecular chains leads to extensive changes of the physico-mechanical and technological properties of various polymers, as compared with the corresponding linear polymers. For example, branched divinylstyrene rubbers, polybutadienes, and other branched elastomers possess a low elasticity, breaking strength, etc. The decrease of strength properties and the change of the dynamic and mechanical properties with the increase of the degree of branching is characteristic for such thermoplastic polymers as polystyrene, polyethylene, polyvinyl chloride, etc. There also exist considerable differences in the rheological properties of linear and branched polymers. For example, at low loads (shear stresses) linear polymers and their melts flow like newtonian fluids and possess a lower viscosity as compared with branched polymers, whereas at high loads the character of flow deviates from that of a newtonian flow, so that the viscosity of a branched polymer is lower than that of a linear polymer or almost equal. Similar regularities have also been observed for concentrated solutions. Hence, the branching, together with the regularity of the structure of polymer chains, the molecular weight, and the molecular weight distribution, represents one of the most important molecular parameters of polymers. The branching occurs during polymerization and is caused essentially by a transfer of active centers to the polymer chain.

Rheological Properties of Multichain Polybutadienes

1965 ◽  
Vol 38 (4) ◽  
pp. 893-906 ◽  
Author(s):  
Gerard Kraus ◽  
J. T. Gruver
Keyword(s):  
Molecular Weight ◽  
Branched Polymers ◽  
Linear Polymers ◽  
Newtonian Viscosity ◽  
Zero Shear Viscosity ◽  
Shear Rates ◽  
Molecular Weights ◽  
High Shear Rates ◽  
Long Chain ◽  
Newtonian Behavior

Abstract The introduction of one or two long chain branches into a polybutadiene molecule to form trichain or tetrachain molecules, respectively, leads to profound changes in Theological behavior. At low molecular weights the Newtonian (zero shear) viscosity is decreased relative to a linear polymer of the same molecular weight. At molecular weights exceeding 60,000 (trichain) or 100,000 (tetrachain), the Newtonian viscosity rises rapidly above the corresponding value for a linear polybutadiene. However, non-Newtonian behavior of the branched polymers becomes more pronounced the higher the molecular weights, so that at moderate to high shear rates the viscosity of the branched polymers is uniformly lower than that of linear polymers of identical molecular weight.

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.

Viscoelastic Properties of Linear Polymers in the High-Elastic State

1972 ◽  
Vol 45 (4) ◽  
pp. 1015-1032
Author(s):  
G. V. Vinogradov ◽  
E. A. Dzyura ◽  
A. Ya Malkin ◽  
V. A. Grechanovskii
Keyword(s):  
Molecular Weight ◽  
Storage Modulus ◽  
Viscoelastic Properties ◽  
Polymer Chains ◽  
Quantitative Relation ◽  
Linear Polymers ◽  
Elastic State ◽  
Thermomechanical Characteristics ◽  
Time Regime ◽  
Temperature Dependences

Abstract The relation between molecular weight, chain rigidity, and the length of the high-elasticity plateau is determined from frequency and temperature dependences of the storage modulus for polybutadienes and polystyrenes with Mw/Mn≤1.1. Use is made of the concept of equivalence of high-elastic states characterized by equal lengths of high-elastic plateaus for linear polymers. The high-elastic states of the linear polymers studied are equivalent if the polymer chains have equal numbers of dynamic segments and if the reference temperature is T0=1.22Tg, where Tg is the glass transition temperature. The viscoelastic properties of the polymers in the high-elastic state are determined unambiguously by Tg and the molecular weight of the dynamic segment. The quantitative relation between thermomechanical characteristics obtained by measuring deformation versus temperature under a constant time regime and dependence of storage modulus versus frequency under isothermal conditions is discussed.

scholarly journals Analytical Rheology of Polymer Melts: State of the Art

2012 ◽  
Vol 2012 ◽  
pp. 1-24 ◽  
Author(s):  
Sachin Shanbhag
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Melts ◽  
State Of The Art ◽  
Branched Polymers ◽  
Linear Polymers ◽  
Rheological Measurements ◽  
Unknown Sample ◽  
Extreme Sensitivity

The extreme sensitivity of rheology to the microstructure of polymer melts has prompted the development of “analytical rheology,” which seeks inferring the structure and composition of an unknown sample based on rheological measurements. Typically, this involves the inversion of a model, which may be mathematical, computational, or completely empirical. Despite the imperfect state of existing models, analytical rheology remains a practically useful enterprise. I review its successes and failures in inferring the molecular weight distribution of linear polymers and the branching content in branched polymers.

scholarly journals A theory relating the action of salts on bacterial respiration to their influence on the solubility of proteins

1947 ◽  
Vol 134 (875) ◽  
pp. 181-201 ◽  
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Dehydrogenase Activity ◽  
Halophilic Bacteria ◽  
Convincing Evidence ◽  
Effect Of Temperature ◽  
Bacterial Respiration ◽  
Concentrated Solutions ◽  
Salting Out ◽  
Intact Cells

Evidence has been presented indicating that the action of concentrated solutions of salts on bacterial respiration may be partly explained in terms of salting-out. It has been suggested that the material upon which this action is exerted is probably one of the proteins concerned in respiration, perhaps a dehydrogenating enzyme. This theory provides satisfactory explanations for: ( a ) the relation between salt con­centration and rate of respiration or dehydrogenase activity; ( b ) the effect of temperature on this relation; and ( c ) the effect of pH on this relation, if it is further supposed that only the zwitterionic fraction of the protein is involved. The relative actions of various salts are in fair agreement with this suggestion, but provide no very convincing evidence either for or against it. The chief point of difficulty lies in the range of concentration over which the action is manifest. With halophilic bacteria, the evidence is consonant with the above view if the protein involved is one of high molecular weight. With normal organisms the salt concentra­tions are much lower than those causing salting-out. There is a little evidence that in normal organisms the dehydrogenating enzymes are less sensitive to salts than the intact cells, which may be the source of the discrepancy. No reason for this can yet be suggested, but the property must be absent from the enzymes of halophilic organisms, and whatever it is, its absence must be the foundation of the halophilic character.

Processability predictions for mechanically recycled blends of linear polymers

2020 ◽  
Vol 40 (9) ◽  
pp. 771-781
Author(s):  
Janne van Gisbergen ◽  
Jaap den Doelder
Keyword(s):  
Molecular Weight ◽  
Circular Economy ◽  
Melt Flow Index ◽  
Building Blocks ◽  
Experimental Designs ◽  
New Method ◽  
Flow Index ◽  
Linear Polymers ◽  
Combined Method

AbstractRecycling of thermoplastic polymers is an important element of sustainable circular economy practices. The quality of mechanically recycled polymers is a concern. A method is presented to predict the structure and processability of recycled blends of polymers based on processability knowledge of their virgin precursor components. Blending rules at molecular weight distribution level are well established and form the foundation of the new method. Two essential fundamental building blocks are combined with this foundation. First, component and blend structure are related to viscosity via tube theories. Second, viscosity is related to melt flow index via a continuum mechanics approach. Emulator equations are built based on virtual experimental designs for fast forward and reverse calculations directly relating structure to viscosity and processability. The new combined method is compared with empirical blend rules, and shows important similarities and also clear quantitative differences. Finally, the new method is applied to practical recycling quality challenges.

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>

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