Oxidative Degradation Process Research Articles

13C NMR study of the microstructure of poly(styrene oxide)s prepared with anionic initiators

AbstractThe tacticity and the nature of irregularities and end‐groups in poly(styrene oxide) samples prepared using potassium alcoholates and anionic coordinated systems as initiators were studied by 13C NMR at 62,89 MHz. It was found that the polymerization initiated with potassium alcoholates fits a first‐order Markov propagation model. Head‐to‐head (HH) and tail‐to‐tail (T‐T) irregularities are detected in all the samples studied, but more than 95% of the opening of the oxirane ring occurs in the β‐position with potassium alcoholates as initiators while about 10% of α‐scission may be observed with coordinated systems. Secondary hydroxyl terminal groups and initiator moieties are identified in polymers prepared with potassium alcoholates. Poly(styrene oxide) was found to undergo chain‐scission by aging at 25°C. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified.

Gas phase oxidation of tetrahydrofuran

AbstractThe slow gas‐phase oxidation of tetrahydrofuran was studied under static conditions at 220°C. The relative amounts of each product, if extrapolated to zero reaction time, show which are the primary reaction products, and the reaction stoichiometry was thus established. Rate constants for hydroperoxides production and consumption were calculated; these hydroperoxides are responsible for chain branching. Carbon monoxide and carbon dioxide have been shown to be formed in the early stages of the reaction and not simply as end products of oxidative degradation processes. It has been found that at reaction times close to zero one tetrahydrofuran molecule may be attacked in one or several carbon atoms. 65.9% of tetrahydrofuran consumed in the first stages of the reaction forms succinic acid through a mechanism in which one molecule of fuel is attacked by two molecules of oxygen. More than 20% of the tetrahydrofuran molecules are attacked at least by three molecules of oxygen.

Polymerization products of p-benzoquinone as bound antioxidants for SBR. Part II—The antioxidizing efficiency

The antioxidizing efficiency of the polymeric products of p-benzoquinone as bound antioxidants for SBR has been investigated by measuring the percentage deterioration of tensile strength and ultimate elongation for the thermally aged rubber samples after up to 14 days in an air oven at 100°C. The results indicate the remarkable antioxidizing efficiency of these products for SBR compared with the common industrial antioxidants. The higher efficiency is attributed to the ability of the polymeric antioxidants to react with the radical intermediates of the oxidative degradation process, thus bonding them chemically to the rubber chains. The effect of the polymeric antioxidants on the rate of sulfur vulcanization has also been studied. The results reveal that, depending on the quinone/hydroquinone ratio of the product, the polymeric antioxidants may accelerate or slightly retard the rate of vulcanization. The results also indicate that blending the polymeric quinones in equal proportions with an amine antioxidant 6PPD leads to a pronounced improvement in the antioxidizing efficiency of the resulting stabilizer without affecting the rheological or other properties of the rubber. A mechanism for the antioxidant action is proposed.

High-Temperature Corrosion Resistance

The approaches which are currently used to develop high-temperature corrosion resistance in alloys are briefly described by considering oxidation, mixed gas, and hot corrosion degradation processes. These approaches are compared to those used to develop high temperature corrosion resistance in ceramics, and future trends that may be expected to be followed to obtain high temperature corrosion resistance are also reviewed.

Oxidative degradation processes in synthetic and biological polymers as studied by pulse radiolysis experiments

On the basis of pulse radiolysis experiments carried out with various polymers in dilute solution three modes of action of molecular oxygen, O2 can be discriminated with respect to main-chain scission: (a) O2 acts as a promoter, (b) O2 acts as an inhibitor, and (c) O2 acts as a fixing agent for main-chain breaks. The promoting mode of action (a) is due to the inhibition of simultaneously occurring intermolecular acrosslinking [DNA, poly(methyl vinyl ketone)] and/or to the combination of peroxyl radicals with the subsequent formation of readily decomposing oxyl radicals (polyethylene oxide, polyacrylamide, polyvinylpyrrolidone, polyribouridylic acid, polyriboadenylic acid, polyribocytidylic acid). The inhibiting mode of action (b) pertains to the reaction of O2 with macroradicals that otherwise undergo main-chain rupture [amylose, poly(methyl methacrylate)]. Fixing of main-chain ruptures (mode c) becomes important, if macroradicals generated by a very fast rupture of bonds in the main chain, are prone to recombine quickly. This mode of action was evidence in the case of polybutenesulfone, where main-chain scission involves the extrusion of small segments of the chain.

Pulse radiolysis studies concerning oxidative degradation processes in linear polymers

On the basis of pulse radiolysis experiments carried out with various polymers in dilute solution three modes of action of molecular oxygen, O 2, can be discriminated with respect to main-chain scission: (a) O 2 acts as a promotor, (b) O 2 acts as an inhibitor, and (c) O 2 acts as a fixing agent for main-chain breaks. The promoting mode of action (a) is due to the inhibition of simultaneously occuring intermolecular crosslinking (DNA, polymethylvinylketone) and/or to the combination of peroxyl radicals with the subsequent formation of readily decomposing oxyl radicals (polyethylene oxide, polyacrylamide, polyvinylpyrrolidone, polyribouridylic acid, polyriboadenylic acid, polyribocytidylic acid). The inhibiting mode of action (b) pertains to the reaction of O 2 with macroradicals that otherwise undergo main-chain rupture (amylose, polymethylmethacrylate). Fixing of main-chain ruptures (mode c) becomes important, if macroradicals generated by a very fast rupture of bonds in the main-chain, are prone to recombine quickly. This mode of action was evidenced in the case of polybutenesulfone where main-chain scission involves the extrusion of small segments of the chain.

Kinetic analysis of the oxidative degradation of polyaryl-orthophosphate

Thermogravimetric study of poly-aryl-orthophosphate indicates that in presence of air the decomposition is a two step process. The first step is the chain scission to form quinone and the subsequent step the oxidation of quinone to maleic anhydride. The kinetic parameters were determined for the oxidative thermal degradation process.

The interconnection between the structural-mechanical and chemical phenomena accompanying oxidative degradation processes in oriented polypropylene

Mechanical stresses accumulate in the surface layers of the specimen during diffusive oxidation of oriented polypropylene and these stresses, in their turn, affect the chemical mechanism. Degradation of chains in the surface layers of thick specimens occurs to a considerably greater extent than in oriented thin film oxidized under analogous conditions. The yield of hydroperoxide per mole of absorved oxygen is less by a factor of 1·6–1·8 in the thick specimens, and the yield of the number of acts of chain scission is greater by a factor of 1·8–2·6 than in the thin film oxidized under analogous conditions. The observed effects are probably connected with the occurrence of oxidation in the field of the mechanical stresses in the case of the thick specimen, a fact which leads to a more important part being played by the decomposition of the radicals R· and RO 2 · reactions which compete with the usual reaction of chain prolongation that leads to the formation of hydroperoxide.

Degradation of Bunker C oil under different coastal environments of Chedabucto Bay, Nova Scotia

The results given in this paper tend to indicate that the extent of degradation of spilled oil in marine areas depends, in a large measure, upon the environmental conditions of coastal areas. The degradation is rapid in the high energy environment but is relatively slow in protected areas. Bacterial as well as oxidative processes appear to alter the composition of oil. Oils exposed to high energy shoreline environments lose n-alkanes more rapidly. This loss is probably due to bacterial degradation because no other known physical or chemical process can account for this. With weathering the saturated and aromatic hydrocarbons decrease with a corresponding increase in the non-hydrocarbons, particularly in resins and NSO compounds. These changes which are possibly due to microbial and oxidative degradation processes are prominent in the oils of high energy environment. The rates of degradation of saturated and aromatic fractions appear to be the same. The specific gravity increases with an increase in degradation of oil. The viscosity values show a marked increase with weathering. The increased viscosity of the oil residues in the high energy environment has reduced its mobility. The data suggest that the residual oils present in varying amounts on nearly all contaminated beaches of the protected areas of low and moderate energy environments will persist for several years. In high energy environments the residual oils are substantially altered due to the loss of n-alkanes and a parallel increase in resins and NSO compounds. The resulting residues are highly viscous and remain adhering to sand and pebble substrate.

Citrate Synthase as a Key Enzyme in the Regulation of Heterotrophic and Autotrophic Metabolism of Rhodopseudomonas

Citrate synthase has been purified from Rhodopseudomonas spheroides. It was found to be an important regulatory enzyme. NADH, a product of the photosynthetic electron transport in this organism, is a strong inhibitor of the enzyme. The kinetic parameter point to an allosteric mechanism. The NADH saturation curve is sigmoid, the Hill coefficient is about 2,0. AMP was found to relieve the NADH inhibition. Without NADH the saturation curve for acetyl-CoA is hyperbolic, the corresponding Hill coefficient is 1,0. In the presence of NADH the acetyl-CoA saturation curve is sigmoid and the Hill coefficient is shifted to 2,0. AMP restores the saturation curve and the Hill coefficient for acetyl-CoA to those obtained in the absence of NADH. In connection with a reciprocal effector relationship of ribulose-5-P kinase with respect to its modulation by NADH and AMP citrate synthase might be regarded as a key enzyme in the regulation and interaction of oxidative degradation processes and carbon assimilation via reductive pentosephosphate cycle.

Studies in the field of polyethylene—IV.: Influence of γ-radiation on the structure and molecular weight of the AS polyethylene

A study was made of effects of 60Co γ-radiation on the average mol. wt. and the structure of AS polyethelene obtained with amyl-sodium catalyst according to the process of C. D. Nenizescu and co-workers. Examination was made of the viscosimetric characteristics, and the i.r. and electron spin resonance (ESR) absorption spectra for samples irradiated at room temperature and in the presence of air. The spectra were recorded immediately after irradiation and after various lengths of storage at different temperatures. The ionizing radiation causes an oxidative degradation of AS polyethylene, shown by the decrease of the average mol. wt., and the appearance of characteristic i.r. absorption bands for oxygen-containing groups. The ESR spectra indicate the existence of allyl, alkyl and polyenyl radicals. During storage of the irradiated AS polyethylene especially at high temperature (80°), a slight increase of the oxidative degradation process can be observed.

Translocation and Degradation of 14C-Labelled Sevin in Cotton Plant

The distribution and metabolic fate of Sevin in cotton plant has been investigated using 14C-insecticide labelled at two different sites. Sevin is readily absorbed by the root system. Hydrolytic and nonhydrolytic mechanisms contribute almost equally to the metabolism of the insecticide. A specific esterase hydrolyzes the ester bond to produce 1-naphthol, methylamine and CO2 (24% of the absorbed dose). The liberated methylamine undergoes partly a process of oxidative degradation to CO2. A major metabolite possessing the skeleton CO-C (O) -N-C is probably produced by hydroxylation of the naphthalene ring

Toxic fluorine compounds. The use of the omega-fluorine atom in the study of the metabolism of fatty acids containing ethyl, n-propyl and isopropyl branches.

1. Some omega-fluoroalkanoic acids containing a branched ethyl, n-propyl or isopropyl group in the alpha- or beta-position have been prepared. 2. A study of the toxicity of these acids revealed that the ethyl group partially inhibited, and the n-propyl and isopropyl groups completely inhibited, the normal processes of oxidative degradation.

Ionisation and irradiation effects in high-voltage dielectric materials

A study of the chemical changes produced by exposure of dielectric materials to high-energy ionising radiation has shown that the effects are similar to those involved in electrical deterioration during stress aging and when ionisation has taken place in the dielectric. The principal effects observed in hydrocarbons and polymeric materials after exposure to radiation are: the crosslinking of the molecules to form an infusible gel structure; the evolution of hydrogen and low-molecular-weight fragments; molecular degradation by main-chain scission; the formation and annihilation of unsaturated groups; and, in the presence of air, processes of oxidative degradation. The corresponding electric stress and ionisation phenomena are: wax or ‘cheese’ formation in solid-type cables; the gas evolving characteristics of paraffinic oils; the embrittlement of insulating paper; the formation of double bonds in aged cable oils, as evidenced by increased absorption in the ultraviolet region; and the oxidation effects with air resulting in an increase in power factor.While the mechanisms of radiation-induced change are not yet completely understood, they should throw light on the corresponding electrical stress and ionisation phenomena. Some of the methods used to protect organic systems against the effects of high-energy radiation are also satisfactory in reducing electrical effects, and a study of these protective mechanisms should be beneficial in the field of high-voltage dielectrics.

Oxidation-Reduction Systems for Initiation of Radical Processes. VI. Systems Involving Oxygen for Initiation of Oxidative Degradation of Polymers

Abstract 1. The mechanism of action of various oxidation-reduction systems containing organic reducing agents, iron salts, and oxygen, is investigated, and it is shown that in hydrocarbon media these systems are an effective source of free radicals at low temperatures. 2. The possibility of utilization of these systems for initiation of a chain process of oxidative degradation of unsaturated and some saturated polymers, at low temperatures, is shown.

X-Ray Investigation of the Crystallization of Vulcanized Rubber on Stretching

Abstract 1. x-Ray methods have been used to investigate the amount of crystalline phase in stretched samples as a function of the vulcanization time. 2. Curves relating the percentage of crystalline phase to the vulcanization time have sharply defined maxima. 3. A comparison of the curves relating tensile strength to vulcanization time with the curves of crystal formation shows their analogous character, the position of the maxima approximately corresponding to one and the same vulcanization time. 4. The position of the maxima on the curves of crystal formation is not related to the degree of stretching. 5. The effect of accelerators is to shift the maximum on the curve of crystal formation to the region of short vulcanization times and to increase the percentage of crystalline phase. 6. The curves of crystal formation and of tensile strength, and thus the behavior of the stress-strain curves for various vulcanization times, is interpreted from the point of view of the existence of two processes—the process of forming a network of cross-links by the interaction of rubber with sulfur, and the process of oxidative degradation of the rubber.