All SBR vulcanizates, when tested in a relaxed state, reacted with ozone of low concentrations to form a film of oxidized products which provided an effective barrier against further attack by gaseous ozone. SBR vulcanizates that were under stress, but which contained no effective antiozonant in their formulation, were readily attacked by ozone. The absorption of ozone appeared to begin with an initial rate of zero which was followed by rapidly increasing rates until a maximum had been reached, when ozone cracks were visible on the surface of the rubber. SBR vulcanizates that were under stress, but which contained an antiozonant, were protected from an attack by ozone to a degree that ranged from poor to excellent. The degree of protection depended (a) on the differential in the rates of reaction of the antiozonant and the rubber hydrocarbon with ozone, (b) on the initial concentration of the antiozonant on the surface of the vulcanizate which reacted with ozone to form a barrier of oxidized residues, and (c) on the rate of effusion of fresh antiozonant from within the rubber to the outer surface of the barrier. SBR vulcanizates containing a naphthenic processing oil as an extender were not so resistant to ozone as standard SBR vulcanizates. It is probable that the effectiveness of the antiozonants tested in these vulcanizates was reduced by their high solubility in the oil phase. SBR vulcanizates containing trioctyl phosphate as a plasticizer were vigorously attacked by ozone. It is possible that the gaseous ozone dissolved to some extent into the plasticizer phase, increasing the concentration of ozone in the area causing a more severe oxidation of the rubber. SBR vulcanizates that had been coated with an antiozonant by dipping the specimen several times into a solution of the antiozonant in a solvent were found to contain a higher concentration of the antioxonant directly on the surface of the vulcanizate than in the case where three parts of the antiozonant were added during vulcanization. A mechanism for the ozonization of SBR vulcanizates has been proposed which includes a possible mechanism for the protective action of antiozonants. A rate equation has been derived from this mechanism which was consistent with the experimental rate data.
Years ago Sawitsch reported that ethyl orthoformate had reacted with acetic anhydride1 to give, not methylidene acetate (CH(OOCCHs)j) as had been expected, but instead formic acid and ethyl acetate. Undoubtedly ethyl formate was formed at the same time.Later Claisen made use of acetic anhydride in the reaction between ethyl orthoformate and ethyl acetoacetate.2•3 In this reaction the product was ethyl -ethoxymethyleneacetoacetate and it has been tacitly assumed that the function of the acetic anhydride was to remove ethyl alcohol, thus permitting the reaction to proceed. This type of reaction works equally well with acetylacetone2 or with diethyl malonate,2 although in the latter case Claisen used zinc bromide as a catalyst.More recently Sah extended this type of condensation to prepare the corresponding products using, instead of the orthoformate the orthoacetate and the orthobenzoate.4 These reactions were also carried out in the presence of acetic anhydride.• Abstracted from the thesis presented by the second author to the faculty of the University of Buffalo in partial fulfillment of the requirements for the degree of
Early work on aliphatic ortho esters, while outlining their preparation and properties, has mentioned as well their instability. Triethyl orthoformate for example is not as stable as are the orthoformates of the higher aliphatic alcohols, but no further suggestions have been advanced on this point to date. Compounds of this type have been prepared from the '1) Presented at the Spring Meeting,
All styrene-butadiene rubber (SBR) vulcanizates, when tested in a relaxed state, reacted with ozone (25 to 500 pphm (parts per hundred million) ozone in air) to form an oxidized film which provided an effective barrier against attack. SBR vulcanizates that were under stress, but which contained no effective antiozonant in their formulation, were readily attacked. The absorption of ozone began with an initial rate of zero but rapidly increased until a maximum rate had been reached when ozone cracks became visible. SBR vulcanizates that were under stress, but which contained an antiozonant, absorbed ozone with a high initial rate which depended on the concentration of the ozone-sensitive materials on the surface of the vulcanizate and on the partial pressure of the gaseous ozone. The rate of absorption declined during the exposure time until a steady low equilibrium rate was reached. The vulcanizates were protected from an attack by ozone (cracking) to a degree which ranged from poor to excellent, and depended (a) on the differential in the rates of reaction of ozone with the antiozonant and the rubber hydrocarbon, (b) on the initial concentration of the antiozonant at the surface of the vulcanizate, and (c) on the rate of effusion of fresh antiozonant from within the rubber to the outer surface of the oxidized barrier. A mechanism is proposed for the protective action of antiozonants in vulcanizates, and a rate equation has been derived from this mechanism which is consistent with the experimental data.
The purple-colored filtrate decomposed and deposited .L dark solid which was insoubIe in the carbon tetrachloride The residue could be extracted with chloroform to yield inore purple 5olutioi1, vhirh tlso drcotnposed in a it.!\ lllllmtes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.