The Crystallization of Vulcanized Natural Rubber at Low Temperatures

1952 ◽  
Vol 25 (3) ◽  
pp. 397-411 ◽  
Author(s):  
E. W. Russell
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Low Temperatures ◽  
Maximum Rate ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Cross Links ◽  
Temperature Rate ◽  
Two Stages ◽  
Natural Rubber Vulcanizates

Abstract A series of natural rubber vulcanizates have been crystallized at −36° − 26° −17.5° and −2° C and the changes followed dilatometrically. As for raw rubber there is a maximum rate of crystallization at about −26° C; vulcanization decreases the rate and alters the shape of the temperature-rate curve. The amount of combined sulfur is the chief factor in determining the rate and extent of crystallization of pure-gum vulcanizates. Cross-linking, where it is efficient so that the chains between the cross-links are chemically unaffected, also depresses the rate and extent of crystallization. The use of vulcanizates which crystallize slowly permits melting to be accomplished at much lower rates of heating than was previously possible with raw rubber. Two stages of melting are distinguished the first occurring under the influence of forces between the crystalline and amorphous regions and the second analogous to the melting of low molecular weight crystalline substances.

Cross-Linking in Natural-Rubber Vulcanizates

1953 ◽  
Vol 26 (4) ◽  
pp. 741-758 ◽  
Author(s):  
H. E. Adams ◽  
B. L. Johnson
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Cross Linking ◽  
Cross Link ◽  
General Validity ◽  
Tetramethylthiuram Disulfide ◽  
Cross Links ◽  
The Cross ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.

Calcium-Dependent Cross-Linking Processes in Platelets

1979 ◽  
Author(s):  
I. Cohen ◽  
T. Glaser
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Tracer Concentration ◽  
Calcium Dependent ◽  
A 23187 ◽  
Polymer Formation ◽  
Total Disappearance ◽  
Low Molecular Weight Proteins

When platelet cytoplasmic Ca2+ is increased by the ionophore A 23187, there is the coincident appearance of a cross-linked polymer and the partial disappearance of five high molecular weight polypeptide bands (> 145,000). The glycoproteins show a partial disappearance of bands lb, IIb and IV and the total disappearance of hands la and Ilia. The disappearance of the protein bands, possibly contributing to the polymer formation, is prevented by histamine, aminoacetonltrile and cystamlne, which, as pseudodonor amines are known Inhibitors of factor XHIa-catalyzed cross-linking. 14C-histamine, at a tracer concentration, was incorporated into the polymer as well as into myosin, glycoproteins IIb and IIIa (α-actinln), actin and two unidentified low-molecular weight proteins. The polymer formed is also apparent in isolated membranes following the iono-phore-stimulated increase in intracellular Ca2+. These findings are unrelated to a proteolytic activity since the platelet Ca2+-dependent proteases are inhibited by leupep-tin. Ca2+-activation of a platelet cytosol transamidase would explain the data obtained. This platelet transamidase(s) may couple membrane proteins to cytoplasmic contra-tlle proteins. Thus, a new concept is proposed for the stabilization of platelet membranes and platelets as they form the hemostatic plug.

Glass Transition and Ultrasonic Relaxation in Polystyrene

1996 ◽  
Vol 455 ◽  
Author(s):  
A. Sahnoune ◽  
L. Piché
Keyword(s):  
Molecular Weight ◽  
Relaxation Time ◽  
Glass Transition ◽  
Low Temperatures ◽  
Relaxation Modulus ◽  
Low Molecular Weight ◽  
Relaxation Model ◽  
Fragility Index ◽  
Molecular Weights ◽  
Ultrasonic Relaxation

ABSTRACTWe present measurements of the glass transition and the ultrasonic relaxation modulus in a series of monodisperse polystyrenes. The temperature dependence of the modulus was analyzed using Havriliak-Negami relaxation model (HN) and Vogel-Tammann-Fulcher equation (VTF) for the relaxation time. The results allowed us to determine the fragility index, m, which decreases with increasing molecular weight, Mn. Furthermore, the relaxation time was found to saturate at high molecular weights and varies as Mnp, in the low molecular weight region. The exponent is p≈2 at high temperatures and p ≈ 7 at low temperatures close to Tg.

scholarly journals Binding Affinity, Cellular Uptake, and Subsequent Intracellular Trafficking of the Nano-Gene Vector P123-PEI-R13

2016 ◽  
Vol 2016 ◽  
pp. 1-8
Author(s):  
Yaguang Zhang ◽  
Hongmei Shu ◽  
Jing Hu ◽  
Min Zhang ◽  
Junweng Wu ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Cellular Uptake ◽  
Intracellular Trafficking ◽  
Transfection Efficiency ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Gene Vector ◽  
Dna Complexes ◽  
Dynamic Source

A nano-gene vector PEI-P123-R13 was synthesized by cross-linking low molecular weight PEI with P123 and further coupling bifunctional peptide R13 to the polymer for targeting tumor and increasing cellular uptake. The binding assessment of R13 toαvβ3 positive cells was performed by HRP labeling. The internalization pathways of P123-PEI-R13/DNA complexes were investigated based on the effect of specific endocytic inhibitors on transfection efficiency. The mechanism of intracellular trafficking was investigated based on the effect of endosome-lysosome acidification inhibitors, cytoskeleton, and dynein inhibitors on transfection efficiency. The results indicated that the bifunctional peptide R13 had the ability of binding toαvβ3 positive cellsin vitro. The modification of P123-PEI-R13 with R13 made it display new property of internalization. P123-PEI-R13/DNA complexes were conducted simultaneously via clathrin-mediated endocytosis, caveolin-mediated endocytosis, macropinocytosis, and possible energy-independent route. After internalization, P123-PEI-R13/DNA complexes could escape from the endosome-lysosome system because of its acidification and further took microtubule as the track and dynein as the dynamic source to be transported toward the microtubule (+) end, to wit nucleus, under the action of microfilament, and with the aid of intermediate filament.

Ozonolytic Degradation of Interpolymers of Natural Rubber with Methyl Methacrylate and Styrene

1958 ◽  
Vol 31 (1) ◽  
pp. 82-85
Author(s):  
D. Barnard
Keyword(s):  
Molecular Weight ◽  
Carbon Black ◽  
Natural Rubber ◽  
Accurate Determination ◽  
Synthetic Polymers ◽  
Polymer Chains ◽  
Low Molecular Weight ◽  
Rubber Content ◽  
Tert Butyl Hydroperoxide

Abstract The preparation of graft and block interpolymers of natural rubber and synthetic polymers has made it desirable that the number and size of polymer chains attached to rubber be readily determinate. The degradation of unsaturated polymers with tert-butyl hydroperoxide in the presence of osmium tet oxide has been used for the determination of free polystyrene in SBR and carbon black in several elastomers, and has recently been applied to the present problem. The accurate determination of the rubber content of interpolymers by quantitative ozonolysis essentially according to the method of Boer and Kooyman suggested that this might be made the basis of isolation of the attached polymer, the rubber being degraded into fragments of low molecular weight, from which the polymer could be separated by conventional techniques. The method should be applicable to any interpolymer, or mixture, of a polyunsaturated and a saturated polymer and is illustrated with reference to interpolymers of natural rubber (NR)-polymethyl methacrylate (PMM) and NR-polystyrene (PS).

Thermodynamics of Crystallization in High Polymers. Natural Rubber

1955 ◽  
Vol 28 (3) ◽  
pp. 718-727 ◽  
Author(s):  
Donald E. Roberts ◽  
Leo Mandelkern
Keyword(s):  
Natural Rubber ◽  
Melting Temperature ◽  
Low Temperatures ◽  
Rapid Heating ◽  
Heat Of Fusion ◽  
Low Molecular Weight ◽  
Heating Rates ◽  
Equilibrium Melting Temperature ◽  
Clapeyron Equation ◽  
Melting Temperatures

Abstract The existence of an equilibrium melting temperature, T0m, at 28 ± 1°, for unstretched natural rubber has been established, using dilatometric methods. The lower melting temperatures previously observed are a consequence of the low temperatures of crystallization and the rapid heating rates employed. From melting point studies of mixtures of the polymer with low molecular-weight diluents, the heat of fusion per repeating unit, ΔHu has been evaluated as 15.3 ± 0.5 cal./g. The values of ΔHu and T0m have then been combined with data of other workers to obtain the following information concerning natural rubber: (1) The variation of melting temperature with applied hydrostatic pressure has been calculated from the Clapeyron equation to be 0.0465° C/atm. (2) The degree of erystallinity resulting from maintaining a sample at 0° until the rate of crystallization is negligible has been calculated, by three independent methods, to be in the range 26 to 31 per cent. (3) Analysis of the stress-strain-temperature relationship has indicated that crystallization is the cause of the large internal energy changes that are observed at relatively high elongations.

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