Cis-Trans Isomerization in Polybutadiene

1957 ◽  
Vol 30 (4) ◽  
pp. 1142-1145
Author(s):  
M. A. Golub
Keyword(s):  
Natural Rubber ◽  
Structural Changes ◽  
Titanium Tetrachloride ◽  
Present Knowledge ◽  
Low Molecular Weight ◽  
High Polymer ◽  
Gutta Percha ◽  
Naturally Occurring ◽  
Trans Isomerization ◽  
Cis And Trans

Abstract About twenty years ago, in an effort to transform natural rubber into gutta-percha, Meyer and Ferri irradiated a solution of Hevea in cyclohexane with ultraviolet light, but were unable to detect any cis-trans isomerization in polyisoprene. Later, Ferri showed that treatment of both Hevea and Gutta with certain chemicals, such as chlorostannic acid and titanium tetrachloride, gave rise to closely resembling products which were considered at the time to have structures intermediate between the two geometric forms of naturally-occurring polyisoprene. These resulting polymers were, however, crosslinked in the course of chemical treatment and probably also cyclized, so that in the light of present knowledge about the cyclizing tendencies of the materials employed, this change cannot be regarded as a genuine interconversion of cis and trans double bonds. No true instance of cis-trans isomerization unaccompanied by other structural changes has been reported heretofore for a high polymer, except for the polyenes which are conjugated structures of relatively very low molecular weight. This communication reports the successful transformation of the cis-1,4 units in polybutadiene into corresponding trans units by means of ultraviolet irradiation in the presence of a suitable sensitizer, which may be any one of a wide variety of organic bromine or sulfur compounds. Surprisingly, this isomerization could not be induced in natural rubber.

Cis-Trans Isomerization in Natural Polyisoprenes

1960 ◽  
Vol 33 (2) ◽  
pp. 445-456 ◽  
Author(s):  
J. I. Cunneen
Keyword(s):  
Sulfur Dioxide ◽  
Natural Rubber ◽  
Ultraviolet Light ◽  
Low Temperatures ◽  
Structural Changes ◽  
Trans Isomers ◽  
Gutta Percha ◽  
Trans Isomerization ◽  
Cis And Trans Isomers ◽  
Cis And Trans

Abstract The cis and trans isomers of many simple olefins and conjugated polyolefins can be interconverted by the action of heat, light, and various catalysts, and in many such systems the changes in geometric configuration can be readily followed and the isomers separated and identified. Previous attempts to isomerize natural rubber and gutta-percha by treatment with ultraviolet light and various chemicals gave no detectable cis-trans isomerization, and in general configurational changes in unconjugated polyolefins have been unknown until recently when Golub converted the cis-1,4 units in polybutadiene into the corresponding trans units. This isomerization was achieved by irradiation of the cis-polymer with ultraviolet light in the presence of various organic bromides and sulfur compounds, but apparently this method did not isomerize natural rubber. In attempts to retard the rate of crystallization of natural rubber at moderately low temperatures—i.e., −10° to −40° C—by the attachment of side groups which would interfere with the molecular packing, it was observed that very small amounts of thiol acids were remarkably effective. This suggested that structural changes other than simply the attachment of side groups were occurring in the polyisoprene molecule. Recently it was found that thiol acids could interconvert the cis and trans forms of a simple trialkyl ethylene—e.g., 3-methylpent-2-ene—and subsequently, the isomerization of natural rubber and gutta-percha by these reagents was also observed. Following this, natural rubber, gutta-percha, squalene and cis and trans forms of 3-methylpent-2-ene have also been isomerized by treatment with sulfur dioxide and allied compounds; this work, including an investigation of the physical properties of the vulcanizates obtained from some of the isomerized polyisoprenes, is described in the present paper.

Statistical Lengths of Rubberlike Hydrocarbon Molecules

1943 ◽  
Vol 16 (3) ◽  
pp. 479-485
Author(s):  
Frederick T. Wall
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Properties ◽  
Hydrocarbon Chain ◽  
Point Of View ◽  
Double Bonds ◽  
Gutta Percha ◽  
Cis And Trans ◽  
Trans Structure ◽  
And Chemical Properties

Abstract It has been known for some time that the pure hydrocarbons of balata (or gutta-percha) and natural rubber have the same chemical composition and chemical properties. Both balata and rubber appear to be polymers of isoprene, (C5H8)n, with the same degree of unsaturation. Their physical properties are sufficiently different, however, to make it clear that their structures must differ in some important respect. Since the molecules contain numerous double bonds, it has been suggested that rubber and balata are geometric isomers. Every fourth bond in a rubber or balata molecule is a double bond, so it follows that the possibilities for geometric isomerism are considerable. It was proposed by Meyer and Mark that natural rubber hydrocarbon has a structure for which the molecular chain is cis with respect to all of the double bonds. Balata (or gutta-percha) is then supposed to have a trans-structure throughout, this view having been verified by Fuller and Bunn. It is the purpose of the present paper to consider, from the point of view of recent theories of rubber elasticity, to what extent these structures explain the differences in physical properties. The method to be employed involves calculation of the root mean square lengths of the cis- and trans-structures, which, when compared to their maximum lengths, should give an indication of their extensibilities. In 1932 Eyring treated the problem of the average square length of a hydrocarbon chain. In the present paper a different derivation of Eyring's equation is given (for illustrative purposes), after which this derivation will be extended to the rubberlike molecules with double bonds.

scholarly journals Characterization of a Natural, Stable, Reversible and Colourful Anthocyanidin Network from Sphagnum Moss Based Mainly on the Yellow Trans-Chalcone and Red Flavylium Cation Forms

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 709
Author(s):  
Helge Berland ◽  
Øyvind M. Andersen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Cell Wall ◽  
Peat Moss ◽  
Sphagnum Moss ◽  
Naturally Occurring ◽  
Two Component ◽  
Colour System ◽  
The Common ◽  
Cis And Trans

Anthocyanins with various functions in nature are one of the most important sources of colours in plants. They are based on anthocyanidins or 3-deoxyanthocyanidins having in common a C15-skeleton and are unique in terms of how each anthocyanidin is involved in a network of equilibria between different forms exhibiting their own properties including colour. Sphagnorubin C (1) isolated from the cell wall of peat moss (Sphagnum sp.) was in fairly acidic and neutral dimethyl sulfoxide characterized by nuclear magnetic resonance (NMR) and ultraviolet–visible (UV–vis) absorption techniques. At equilibrium, the network of 1 behaved as a two–component colour system involving the reddish flavylium cationic and the yellow trans–chalcone forms. The additional D- and E-rings connected to the common C15-skeleton extend the π-conjugation within the molecule and provide both bathochromic shifts in the absorption spectra of the various forms as well as a low isomerization barrier between the cis- and trans-chalcone forms. The hemiketal and cis-chalcone forms were thus not observed experimentally by NMR due to their short lives. The stable, reversible network of 1 with good colour contrast between its two components has previously not been reported for other natural anthocyanins and might thus have potential in future photochromic systems. This is the first full structural characterization of any naturally occurring anthocyanin chalcone form.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

scholarly journals Increased cytotoxicity of normal rabbit serum for lectin-resistant mutants of animal cells.

1984 ◽  
Vol 160 (4) ◽  
pp. 1241-1246
Author(s):  
C Jones
Keyword(s):  
Structural Changes ◽  
Chinese Hamster ◽  
Rabbit Serum ◽  
Cytotoxic Action ◽  
Normal Rabbit Serum ◽  
Animal Cells ◽  
Naturally Occurring ◽  
Alternate Complement Pathway ◽  
Surface Carbohydrates ◽  
Naturally Occurring Antibodies

Plant lectins are cytotoxic and can be used to select for mutants of animal cells that exhibit structural changes in cell surface carbohydrates reflecting glycosylation defects. We isolated eight lectin mutants of Chinese hamster ovary (CHO) cells that appear to represent three different phenotype classes. These lectin mutants were much more sensitive to the cytotoxic action of normal rabbit serum (NRS) than were the parental cells. This increased cytotoxicity was heat sensitive, specifically absorbed, and inhibited by simple and complex carbohydrates. No killing was observed under conditions in which only the alternate complement pathway was active. An NRS-resistant subclone that was isolated from one lectin mutant was shown to have also regained wild type behavior when tested with the lectins. The possibility that naturally occurring antibodies in rabbit serum are reacting with incomplete carbohydrate chains on the surface of the lectin mutants is discussed.

Characterizing the naturally occurring sacrificial bond within natural rubber

Polymer ◽  
2019 ◽  
Vol 161 ◽  
pp. 41-48 ◽  
Author(s):  
Xuan Fu ◽  
Cheng Huang ◽  
Yong Zhu ◽  
Guangsu Huang ◽  
Jinrong Wu
Keyword(s):  
Natural Rubber ◽  
Naturally Occurring

scholarly journals A Review on Polyamines and Biotic Stresses in Plants

2018 ◽  
Vol 6 (5) ◽  
Author(s):  
Md Azizul Islam ◽  
Pulak Maitra ◽  
Dipa Mandal
Keyword(s):  
Biotic Stress ◽  
Negative Charge ◽  
Science Research ◽  
Plant Science ◽  
Low Molecular Weight ◽  
Biological Functions ◽  
Membrane Stabilization ◽  
Biotic Stresses ◽  
Naturally Occurring ◽  
Recent Advancement

The biotic stresses are one of the main causes to the loss of crops, and their development, growth and productivity in the environment. Polyamines are positively charge compounds that have active potential power to DNA, RNA and protein (negative charge compounds), are exist in all living life for their low molecular weight and smallness. Naturally occurring polyamines are involved biotic stress response especially different plants disease and contribute the survival of plant in environment. They contribute a lot of different biological functions, such as controlling the cell cycle, protecting the cell, involve in gene expression, cell signaling replication, transcription, translation and membrane stabilization. This article specially highlights the recent advancement of polyamines in modern plant science research their impact of biotic stress specially the diseases caused by different microorganisms (bacteria, fungus) and creature systems.

Characterization of Sol and Gel in Hevea Natural Rubber

1997 ◽  
Vol 70 (5) ◽  
pp. 707-713 ◽  
Author(s):  
Jitladda Tangpakdee ◽  
Yasukuki Tanaka
Keyword(s):  
Molecular Weight ◽  
Weight Fraction ◽  
Toluene Solution ◽  
Low Molecular Weight ◽  
Branch Points ◽  
Gel Content ◽  
High Ammonia ◽  
Linear Molecules ◽  
Cis And Trans

Abstract The gel content of rubber from high-ammonia latex (HA-latex) decreased significantly after deproteinization with proteolytic enzyme. The addition of 1–2% ethanol in toluene solution reduced the gel content of rubbers from HA-latex, deproteinized HA-latex (HA-DP) and pale crepe. Transesterification of the rubber in toluene solution with sodium methoxide dissolved the gel fraction. The gel fractions solubilized after transesterification showed molecular weight distribution rich in low molecular-weight fraction. The Huggins k′ constant of the fractionated rubbers from solubilized-gels was in the range of 0.42–0.45, lower than that of the fractionated HA-DP of 0.5–0.8. This indicates that all the branch-points were decomposed by transesterification to form linear molecules. The Mn values of rubber chains assembling the gel was 5.5−8.3×105 by 13C-NMR measurements of the ratio between cis- and trans-isoprene units, which were comparable to the molecular weight between crosslinks, Mc, of 7−11×105 by swelling measurements. These findings suggest that the branching and crosslinks are composed of two types of branch-points, i. e. one by association or aggregation of proteins or oligopeptides at the initiating end and the other by ester linkages including phosphoric ester at the terminal end.

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