The Rubber Hydrocarbon in Freshly Tapped Hevea Latex

1951 ◽  
Vol 24 (4) ◽  
pp. 737-749 ◽  
Author(s):  
George F. Bloomfield
Keyword(s):  
Molecular Weight ◽  
Intrinsic Viscosity ◽  
Weight Distribution ◽  
Hevea Brasiliensis ◽  
Major Part ◽  
Structural Changes ◽  
Solution Viscosity ◽  
Cross Linking ◽  
High Polymer ◽  
Broad Distribution

Abstract The rubber hydrocarbon in latex as it leaves the tree is already a high polymer, with a broad distribution of molecular weight ranging from several millions to below 100,000, with the major part of the hydrocarbon in the higher molecular weight ranges. Changes in the hydrocarbon subsequent to its leaving the tree tend to be degradative, but may also involve cross-linking reactions leading to changes in plasticity. Structural changes in rubber attributed to restricted cross-linking have a greater influence on plasticity than on solution viscosity. A gel component (probably microgel) present in the freshly tapped hydrocarbon is of considerable importance in determining the hardness of raw rubber, but greatly complicates the interpretation of viscometric data, of which evaluation by the equation: [η]=5.02×10−4 M0.67 only appears to be valid for gel-free rubber fractions. Plasticity and intrinsic viscosity cannot, therefore, be generally correlated, although the plasticity is influenced by the spread of the molecular-weight distribution into lower molecular weight regions. The presence of a high proportion of microgel in latex of untapped trees and of branches remote from the tapping panel of trees in regular tapping, and the presence of combined oxygen in the low-molecular fractions of rubber hydrocarbon obtained from both normal and microgel latexes may be of interest in connection with questions of biosynthesis and metabolism of the rubber hydrocarbon of Hevea brasiliensis.

The kinetics of the polymerization of sarcosine carbonic anhydride

1949 ◽  
Vol 199 (1059) ◽  
pp. 499-517 ◽  
Keyword(s):  
Molecular Weight ◽  
Equilibrium Constant ◽  
Intrinsic Viscosity ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Intermediate Compound ◽  
Preparative Method ◽  
Kinetics Of

The polymerization of carbonic anhydrides, a reaction important but>u as a preparative method for the synthesis of polypeptides and as an example of a less familiar type of polymerization, has been studied in detail using sarcosine carbonic anhydride (I). The propagation reaction has been shown to involve a reversibly formed compound between the carbonic anhydride and the polymer; this compound decomposes by both a unimolecular and a bimolecular route. The equilibrium constant for the formation of the intermediate compound, and both velocity constants for its decomposition have been determined in two solvents, and the energies of activation and frequency factors calculated. The molecular weight distribution has been calculated; it is extremely sharp. The viscosities of the polymers prepared by this reaction have been measured, and the relation between the intrinsic viscosity and the molecular weight established.

Revisit to the intrinsic viscosity-molecular weight relationship of ionic polymers. 5. Further studies on solution viscosity of sodium poly(styrenesulfonates)

1991 ◽  
Vol 24 (23) ◽  
pp. 6156-6159 ◽  
Author(s):  
Junpei Yamanaka ◽  
Hidemasa Araie ◽  
Hideki Matsuoka ◽  
Hiromi Kitano ◽  
Norio Ise ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Intrinsic Viscosity ◽  
Solution Viscosity ◽  
Ionic Polymers ◽  
Weight Relationship ◽  
Relationship Of

Gel Permeation Chromatography of Natural Rubber

1972 ◽  
Vol 45 (1) ◽  
pp. 346-358 ◽  
Author(s):  
A. Subramaniam
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Weight Distribution ◽  
Hevea Brasiliensis ◽  
Distribution Curve ◽  
Gel Permeation Chromatography ◽  
Bimodal Distribution ◽  
Fractional Precipitation ◽  
Molecular Weights ◽  
Gel Permeation

Abstract The Waters Model 200 Gel Permeation Chromatograph has been used to study the molecular weight distribution of natural rubber. The cumulative weight distribution curve of synthetic cis-polyisoprene from the GPC method showed fair agreement with the distribution obtained by fractional precipitation. For natural rubber the agreement was not so good. Natural rubber samples from six clones of Hevea Brasiliensis were examined with the GPC. Differences were observed in their distributions. Five clones showed a distinct bimodal distribution. The weight and number average molecular weights from the GPC were found to be too low. Some possible reasons for this have been suggested.

Gel formation and molecular weight distribution in long-chain polymers

1954 ◽  
Vol 222 (1151) ◽  
pp. 542-557 ◽  
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Average Molecular Weight ◽  
Cross Linking ◽  
Average Weight ◽  
Gel Formation ◽  
Theoretical Derivation ◽  
Experimental Values ◽  
Long Chain

In long-chain polymers an insoluble network or gel may be produced when a number of the separate molecules are linked together. A theoretical derivation is given of the relationship between the amount of gel formed and the degree of cross-linking, in terms of the initial molecular weight distribution. It is shown that whatever the initial molecular weight distribution, incipient gelling occurs when there is on the average one cross-linked monomer per weight average molecule. The shape of the gel-cross-linking curve depends on the ratio of z average, z +1, . . . average molecular weight to the weight average. From experimental values of the curve it becomes possible to determine many of the constants of the molecular weight distribution in the original polymer. Expressions are derived for the number average, weight average and z average of the polymer as a function of cross-linking prior to gel formation, as well as the number and weight averages of the sol fraction after gelation. The average molecular weight between cross-links in the gel is calculated. A number of other functions of the sol and gel fractions are also given.

scholarly journals Molecular Weight Distribution and Intrinsic Viscosity of Sonicated and Successively Fractionated Double-Stranded Deoxyribonucleic Acid and Polyribonucleotides

1994 ◽  
Vol 26 (3) ◽  
pp. 291-302 ◽  
Author(s):  
Masato Tanigawa ◽  
Nobuaki Mukaiyama ◽  
Satoshi Shimokubo ◽  
Kengo Wakabayashi ◽  
Yoshimasa Fujita ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Intrinsic Viscosity ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Deoxyribonucleic Acid

Molecular weight – viscosity relationships for a broad molecular weight distribution polymer

1985 ◽  
Vol 63 (1) ◽  
pp. 221-222 ◽  
Author(s):  
H. Kh. Mahabadi ◽  
L. Alexandru
Keyword(s):  
Molecular Weight ◽  
Bisphenol A ◽  
Intrinsic Viscosity ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Simple Method ◽  
Broad Molecular Weight Distribution

A novel and simple method is described for evaluation of molecular weight – viscosity relationships for a polymer where only broad molecular weight distribution samples are available. The method demands measurement of the intrinsic viscosity and GPC chromatograms of several samples. Results of applying the procedure to bisphenol A – Diethyleneglycol (50:50) copolycarbonate are presented.

Model Elastomers

1997 ◽  
Author(s):  
Burak Erman ◽  
James E. Mark
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Networks ◽  
Length Distribution ◽  
Quantitative Information ◽  
Cross Linking ◽  
Cross Links ◽  
End Linking ◽  
The Cross

Until quite recently, there was relatively little reliable quantitative information on the relationship of stress to structure, primarily because of the uncontrolled manner in which elastomeric networks were generally prepared. Segments close together in space were linked irrespective of their locations along the chain trajectories, thus resulting in a highly random network structure in which the number and locations of the cross-links were essentially unknown. Such a structure is shown in figure 10.1. New synthetic techniques are now available, however, for the preparation of “model” polymer networks of known structure. More specifically, if networks are formed by end linking functionally terminated chains instead of haphazardly joining chain segments at random, then the nature of this very specific chemical reaction provides the desired structural information. Thus, the functionality of the cross links is the same as that of the end-linking agent, and the molecular weight Mc between cross-links and the molecular weight distribution are the same as those of the starting chains prior to their being end-linked. An example is the reaction shown in figure 10.2, in which hydroxyl-terminated chains of poly(dimethylsiloxane) (PDMS) are end-linked using tetraethyl orthosilicate. Characterizing the un-cross-linked chains with respect to molecular weight Mn and molecular weight distribution, and then carrying out the specified reaction to completion, gives elastomers in which the network chains have these characteristics; in particular, a molecular weight Mc between cross-links equal to Mn, a network chain-length distribution equal to that of the starting chains, and cross-links having the functionality of the end-linking agent. It is also possible to use chains having a known number of potential cross-linking sites placed as side chains along the polymer backbone, so long as their distribution is known as well. Because of their known structures, such model elastomers are now the preferred materials for the quantitative characterization of rubberlike elasticity. Such very specific cross-linking reactions have also been shown to be useful in the preparation of liquid-crystalline elastomers. Trifunctional and tetrafunctional PDMS networks prepared in this way have been used to test the molecular theories of rubber elasticity with regard to the increase in non-affineness of the network deformation with increasing elongation.

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