Degradation of polymeric

Degradation of Polymeric Propellant Binders , Final Rept, under Contract N00017-74-C-4335 (1975) 39) W. Brenner B. Rugg, Feasi-... 

In contrast to the extensive work of the pure thermal degradation of polymers, less fundamental chemical information is available on the mechanism of oxidative degradation of polymeric materials. As another point of... 

A mathematical model has been developed which allows the calculation of the degradation of polymeric drug delivery systems. The model has been shown to accurately simulate both the drug release and molecular weight changes in such systems. The concentration of anhydride levels affect the erosion characteristics of... 

Rau J, Maris B, Kinget R et al (2002) Enhanced anaerobic degradation of polymeric azo compounds by Escherichia coli in the presence of low-molecular-weight redox mediators. J Pharm Pharmacol 54 1471-1479... 

In view of the results obtained by Bell and Friedman (136) it is possible that sunlight could bring about a photochemical solubilisation of Pu(IV) polymers. These workers obtained 13 % degradation of polymeric plutonium in the presence of organic materials in one hour when the polymer (0.0093m Pu in 0.47m HC104) was irradiated at 260—280 nm. This degradation rate was four times faster than that observed over a similar period of time in the absence of the UV source. 

Zee, M.E. van der, Stoutjesdijk, J.H., Fell, H. and Feijen, J. (1998b). Relevance of aquatic biodegradation tests for predicting degradation of polymeric materials during biological waste treatment. Chemosphere, 36(3), 461 73. 

In comparison, no structural modification of model B was seen before 120 h of aging (80 °C). However, after 120 h two small doublets appeared in the NMR spectrum and several additional peaks became noticeable in the NMR spectrum. It was determined by NMR and IR spectroscopy that the hydrolysis products were an imide/carboxylic acid and an imide/anhydride. Model B was then aged for 1200 h at 80 °C to quantitatively determine the amount of hydrolysis products as a function of time. The relative intensity of the peaks due to carboxylic acid is constant after some time. The authors suggest that an equilibrium occurs between model B and the products formed during hydrolysis, and therefore, the conversion to hydrolysis products is limited to about 12%. This critical fraction is probably enough to cause some degradation of polymeric materials, but research on six-membered polyimides has remained active. 

Polyvinylimidazoles are effective anti-oxidants for copper at elevated temperatures. Below 250° C, there is no major degradation of the coated polyvinylimidazole films on copper. Furthermore, degraded polyvinylimidazole films can suppress oxidation even at 400 C. Finally, polyvinylimidazoles are more effective anti-oxidants than benzotriazole and imidazoles at elevated temperatures. It is also demonstrated that FT-IRRAS is a useful technique to study degradation of polymeric coatings and corrosion of metal simultaneously. 

Thus, for the degradation of polymeric lignin by the enzyme, two major questions were left (i) Can lignin peroxidase, by itself, depolymerize polymeric lignin without repolymerization or not (ii) Can lignin peroxidase cleave aromatic rings and /J-0-4 bonds of polymeric lignin, or not ... 

Huang-Lee, L. L. H., Cheung, D. T., and Nimni, M. E. (1990). Biochemical changes and cytotoxicity associated with the degradation of polymeric glutaraldehyde derived crosslinks. J. Biomed. Mater. Res. 24,1185-1201. 

Drag reduction decreases with flow time — which is in most application undesirable — and is obviously caused by a degradation of the polymer chain. Degradation of polymeric additives in turbulent flow cannot be easily understood on the basis of present knowledge, i.e., predictions towards the onset of chain scission cannot yet be made. These difficulties can be attributed, on the one hand, to the complex fluid structure and, on the other hand, to the fact that both shear and tensile stresses act simultaneously in turbulent flows. 

Block Copolymers from Prepolymers Synthesized by Partial Degradation of Polymeric Azo Compounds... 

Calculation of the Endocellulase Activity from the Intrinsic Viscosity Values. The enzymic degradation of polymeric substrates can occur at different bonds in the same substrate molecule, and the enzymic activity has to be defined here as the initial number of moles of glyco-sidic bonds split per second (53). This definition corresponds to the definition of the katal, symbolyzed kat. This unit is defined as the catalytic amount of any catalyst (including any enzyme) that catalyzes a reaction rate of one mole per second in an assay system (54), and it is recommended by the International Union of Pure and Applied Chemistry (55) for the quantitative evaluation of catalytic activities. 

Degradation of Polymeric Coatings Studied by Positron Annihilation Spectroscopy. ... 

In the absence of tin less asphaltene is produced which manifests itself as Increased yields of THF insolubles and preasphaltenes. At this time the activity of iron is not completely certain as no effects have been observed on the reactions of the coal derived products. However the proven ability of iron to both catalyze the reactions of some ethers while suppressing propagation reactions of phenoxy radicals suggests that its major activity is probably restricted to the first minutes of reaction (reactions 1,2) and to the slow catalytic degradation of polymerized material. The iron-tin synergism (1) can be interpreted as a co-operative action... 

Hillman, D.E., Lindley, H.M., Paul, J.I. and Pickles, D. (1975) Application of gel permeation chromatography to the study of shear degradation of polymeric viscosity index improvers used in automotive engine oils. Er. Polym. J. 1 397-407. 

Three methods that were used to measure the chemical changes associated with oxidative degradation of polymeric materials are presented. The first method is based on the nuclear activation of lsO in an elastomer that was thermally aged in an, 802 atmosphere. Second, the alcohol groups in a thermally aged elastomer were derivatized with trifluoroacetic anhydride and their concentration measured via 19F NMR spectroscopy. Finally, a respirometer was used to directly measure the oxidative rates of a polyurethane foam as a function of aging temperature. The measurement of the oxidation rates enabled acceleration factors for oxidative degradation of these materials to be calculated. 

Although the QCM has been used to quantitate the mechanisms of enzymatic reactions in some instances, more often it has been used to determine the overall rates and characteristics of products formed in these reactions. For example, multistep processes have been studied that are involved in the enzymatic degradation of polymeric films formed from poly(L-lactide) [61] and poly(3-hydroxybutyrate) [60]. In QCM studies at a high resonance frequency, 27 MHz, DNA polymerase was studied using immobilized DNA to obtain rate constants for three individual steps in the mechanism of this enzymatic reaction ( [65] Chap. 10 in this volume). 

In addition to gasification, other oxidative treatments of plastic and rubber wastes, excluding total combustion, are described in this chapter. These methods, although relatively unknown, may be of great interest in the future for the chemical degradation of polymeric wastes. 

Other interesting solids for the catalytic degradation of polymeric wastes are the various silica-based mesophases which have recently been discovered.4,5 These materials are characterized by the presence of ordered and regular pore systems and high surface areas, typically over 1000 m2 g l. The most common member of this family is MCM-41, which has a hexagonal array of uniform pores with diameters that can be tailored in the range 1.5-10 nm by varying the synthesis conditions. These mesoporous materials can be prepared with a wide... 

K. Pielichowski and J. Njuguna. Thermal Degradation of Polymeric Materials. Rapra Technology, Rapra Technology Ltd., UK, 2005, p. 20. 

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