Mechanical Chain-Scission in Rubber Vulcanizate at Low Temperatures

1979 ◽  
Vol 52 (4) ◽  
pp. 773-780 ◽  
Author(s):  
T. Kusano ◽  
K. Kobayashl ◽  
K. Murakami
Keyword(s):  
Free Radicals ◽  
Chain Length ◽  
Low Temperatures ◽  
Crosslink Density ◽  
Glassy State ◽  
Chain Scission ◽  
Molecular Chain ◽  
Yield Strain ◽  
Air Stream ◽  
Intermolecular Reaction

Abstract When vulcanized natural rubbers are forced to extend in the glassy state, free radicals are produced by the scission of the primary chain. The amount of the free radicals increases with the strain. The tensile yield strain decreases with the decrease of the molecular chain length between crosslinks. This behavior is explainable on the basis of the limited chain extensibility. The extended chains are broken with further increases of the strain. The mechanically produced free radicals are quite stable below about −40°C. The crosslink density of the chain-ruptured material increases about 2∼3×10−5 mol/cm3. This fact shows that the free radicals are consumed not only by recombination but by the intermolecular reaction. In both sulfur and DCP vulcanizates, the network chains rather than the crosslinks are broken by stretching. In an air stream, some free radicals react with oxygen and others form crosslinks.

Degradation of Rubber by Chemical Agents in Solution

1961 ◽  
Vol 34 (4) ◽  
pp. 1212-1219
Author(s):  
G. H. Foxley
Keyword(s):  
Free Radicals ◽  
Low Temperatures ◽  
Model Compound ◽  
Polymer Degradation ◽  
Chain Scission ◽  
Redox Systems ◽  
Chemical Agents ◽  
The Subject ◽  
Partial Fulfillment

Abstract It is clear that the subject of polymer degradation by chemical agents is an active branch of polymer chemistry. This is reflected in the large number of patents applying to polymer degradation and no attempt has been made to include every appropriate patent. Much of the comparative work is based on equal weights, rather than equal numbers of molecules, so that the true comparisons of the efficiency of peptizers are often difficult. It has been shown that polymer degradation can proceed via several mechanisms all of which involve free radicals and the main points can be summarized as follows :— In solutions at low temperatures the initiatory free radicals come from the added peptizer such as benzoyl peroxide or bis-azoisobutyronitrile. Although oxygen accelerates the reaction, it is not essential, and there is appreciable degradation in the absence of oxygen. Thiols are active only when oxygen is present even at high temperature. This is somewhat surprising, since the rubber radicals produced by thermal scission should be just as active as those produced by mastication and be capable of reaction with thiols, and serves to emphasize the importance of the role of oxygen in peptization by thiols and disulfides. Oxygen is also necessary for degradation by redox systems and in its absence structurizing takes place. The lack of work on triphenyl methane derivatives is somewhat surprising in view of the ease with which they undergo homolysis to give free radicals. However, it is not sufficient to introduce any type of free radical and expect degradation: stabilized free radicals are the best peptizers, unstable radicals can add to olefinic bonds and cause crosslinking rather than chain scission. Squalene has been used as a model compound for the study of the reactions of natural rubber with free radicals in a similar manner to the use of methylcyclohexene as a model compound for oxidation studies. This review forms part of a dissertation submitted in partial fulfillment of the requirements for the London University M.Sc. (External) Examination.

E.s.r. studies on free radicals generated in poly[p-(2-hydroxyethoxy) benzoic acid] fibres at low temperatures

Polymer ◽  
1981 ◽  
Vol 22 (9) ◽  
pp. 1267-1271 ◽  
Author(s):  
Toshihiko Nagamura ◽  
Kenneth Lawrence DeVries
Keyword(s):  
Free Radicals ◽  
Benzoic Acid ◽  
Low Temperatures

PHOTOLYSIS OF POLYMETHACRYLIC ACID IN AQUEOUS SOLUTIONS

1964 ◽  
Vol 42 (3) ◽  
pp. 522-531 ◽  
Author(s):  
C. H. Chou ◽  
H. H. G. Jellinek
Keyword(s):  
Aqueous Solutions ◽  
Chain Length ◽  
Polymer Chain ◽  
Irradiation Time ◽  
Polymer Concentration ◽  
Chain Scission ◽  
Polymer Chains ◽  
Polymethacrylic Acid ◽  
Degree Of Ionization ◽  
Ph Values

The photolysis of polymethacrylic acid was studied in aqueous solutions as a function of pH, polymer concentration, polymer chain length, and small additions of electrolytes in the absence of oxygen with light of wavelength 2537 Å. The random chain scission constants decrease with increasing pH values. Small variations in polymer chain length and concentration and electrolyte concentration have no effect on the photolysis. Changes in the ultraviolet spectra with irradiation time are more pronounced at low pH values than higher ones. It is shown that the decrease in susceptibility to photolysis with increasing degree of ionization of the acid is not proportional to the decrease or increase of the number of COOH or COO− groups respectively. It is rather due to the same causes—that is changes in ionic atmosphere— which make the polymer chains uncoil with increasing ionization.

The Dielectric Properties of Symmetrical Long-Chain Secondary Alcohols in the Solid State

1951 ◽  
Vol 4 (2) ◽  
pp. 213 ◽  
Author(s):  
RL Meakins ◽  
RA Sack
Keyword(s):  
Hydrogen Bonding ◽  
Solid State ◽  
Dielectric Loss ◽  
Low Temperatures ◽  
Room Temperature ◽  
Molecular Chain ◽  
Hydroxyl Groups ◽  
Crystal Formation ◽  
Secondary Alcohols ◽  
Long Chain

Symmetrical long-chain secondary alcohols in the solid state show very high dielectric loss at audio and radio frequencies. This can be explained by the presence of chains of hydroxyl groups linked by hydrogen bonding and capable of reversing their direction. Further evidence of hydrogen bonding is provided by a study of the melting points of the secondary alcohols and related compounds. The amount of dielectric loss depends markedly on the manner of formation of the solid, being smallest for samples formed by recrystallization from solvents at low temperatures and largest for specimens obtained by slow cooling from the melt. The alcohols of molecular chain-lengths of 13, 15,17, and 19 carbon atoms show a considerable decrease of absorption on storing at room temperature. For alcohols of between 23 and 43 carbon atoms the loss is rather smaller with a peak at higher frequencies, but remains more constant in time. These results are interpreted in terms of competing influences of van der Waals forces and hydrogen bonds during crystal formation ; the former, which lead to a structure unsuitable for the formation of hydrogen-bond chains, are predominant at low temperatures, but become more rapidly neutralized by thermal motion, especially for the shorter molecules. The high temperature modification of the lower homologues is unstable at room temperature, and a molecular diffusion process causes the bond chains to break. Dilute systems of secondary alcohols with hydrocarbons or paraffin wax of similar molecular chain-length show very small dielectric loss suggesting a solid solution in which bond chains cannot be formed ; if the paraffin molecules are appreciably longer, the absorption is large and decreases on storing, presumably owing to the presence of a pure alcohol phase. I.

Properties of Cotton Fabrics Crosslinked with Different Molecular Chain Lengths of Aldehyde Agents

1992 ◽  
Vol 62 (9) ◽  
pp. 547-551 ◽  
Author(s):  
Tsang-Yuh Liang ◽  
Jenn-Yann Hwang ◽  
Der-Shiann Ju ◽  
Cheng-Chi Chen
Keyword(s):  
Activation Energy ◽  
Chain Length ◽  
Cotton Fabric ◽  
Crosslinking Agent ◽  
Cotton Fabrics ◽  
Molecular Chain ◽  
Diffusion Resistance ◽  
Adsorption Time ◽  
Untreated Cotton ◽  
Chain Lengths

Adsorption time curves from finite baths have been studied for untreated cotton fabric and cottons treated with differing molecular chain lengths of aldehydes (formaldehyde and glutaraldehyde). Crosslinking reduced the rate constant, structural diffusion resistance constant, and equilibrium adsorption of dyeing. Additionally, these data decreased with increasing agent concentration and with increasing molecular chain length of the crosslinking agent. The dyeing activation energy of the glutaraldehyde treated fabric was lower than that of the formaldehyde treated fabric.

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