Polymer degradation material

Functional dyes (1) of many types are important photochemical sensitizers for oxidation, polymerization, (polymer) degradation, isomerization, and photodynamic therapy. Often, dye stmctures from several classes of materials can fulfiH a similar technological need, and reviewing several dye stmctures... 

Because the polymer degrades before melting, polyacrylonitrile is commonly formed into fibers via a wet spinning process. The precursor is actually a copolymer of acrylonitrile and other monomer(s) which are added to control the oxidation rate and lower the glass transition temperature of the material. Common copolymers include vinyl acetate, methyl acrylate, methyl methacrylate, acrylic acid, itaconic acid, and methacrylic acid [1,2]. 

An alternative tactic to deal with the problem of polymer wastes is to make polymers degradable. The difficulty with this approach is that in making synthetic polymers degradable one of the greatest assets of these materials, namely their durability, may be eliminated. There is also the possibility that... 

Based on these studies, it is obvious that poly(N-acylhydroxy-proline esters) are very slowly degrading polymers. These materials may therefore be useful for long-term applications, such as implantable, multiyear contraceptive formulations. For such applications the degradation rates of poly (lactic acid)/poly (glycolic acid) devices would probably be too rapid. 

Conventional XRF analysis uses calibration by regression, which is quite feasible for known matrices. Both single and multi-element standards are in use, prepared for example by vacuum evaporation of elements or compounds on a thin Mylar film. Comparing the X-ray intensities of the sample with those of a standard, allows quantitative analysis. Depending on the degree of similarity between sample and standard, a small or large correction for matrix effects is required. Calibration standards and samples must be carefully prepared standards must be checked frequently because of polymer degradation from continued exposure to X-rays. For trace-element determination, a standard very close in composition to the sample is required. This may be a certified reference material or a sample analysed by a primary technique (e.g. NAA). Standard reference material for rubber samples is not commercially available. Use can also be made of an internal standard,... 

Act physically by stabilising polymers degrading by photolysis. Photons absorbed by chromophores (Ch) present in the plastics material raise the energy level of... 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

The polymer degradation scheme discussed above and shown in Figure 1 is valid in polymers without any additives. However, most commercially available materials are doped with UV absorbers and with light and thermal stabilizers in order to extend their lifetime. The HAS rank among the most important additives used for light and heat stabilization of polymers [9,15,16]. Most commercially available HAS stabilizers are 4-substituted 2,2,6,6-tetramethylpiperidines, as shown below [17],... 

Polymer degradation, which reflects changes in the properties of polymers due to chemical processes that occur as a function of a complex set of environmental conditions, is a challenging topic of great fundamental and technological importance. Historically, materials were used long before their properties were fully understood. In recent years, analytical tools such as microscopy, imaging, and computational techniques have made possible the determination of structural and functional details of materials, some of which are hard to obtain by other methods. 

In order to improve the mechanical properties of PHB or poly(3HB-co-3HV), many have reported on blending these biopolymers with other, both degradable as well as non-degradable, materials. However, due to the lack in compatibility between most polymers no substantial improvements in mechanical properties were reported upon, up to now [90]. 

S. Tsuge and H. Othani, Structural characterization of polymeric materials by pyrolysis GC/MS, Polym. Degrad. Stab., 58, 109 130 (1997). 

Care must be taken when choosing an oil for rubber processing to ensure that its content of polar fractions is low. These polar fractions contain some of the most chemically active compounds in the oil. Polar materials are thought to interfere with cure characteristics and play a part in polymer degradation. These effects will also be accompanied by a drastic reduction in weather resistance, although usually heat resistance is not affected. 

The products of perfluorination are both white, very different from the original black hydrocarbon polymers. Both materials are moisture-sensitive powders and slowly degraded by atmospheric moisture, 6 more quickly than 5. The materials oxidize iodide ion to iodine owing to the presence of the N—F moiety. A series of iodometric titrations showed that 6 required twice the number of equivalents of titrant as did 5. This result supports the proposed structures 6 having twice as many N—F moieties as 5. 

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