Poly oxidative stability

As with the polysulphones, the deactivated aromatic nature of the polymer leads to a high degree of oxidative stability, with an indicated UL Temperature Index in excess of 250°C for PEEKK. The only other melt-processable polymers in the same league are poly(phenylene sulphides) and certain liquid crystal polyesters (see Chapter 25). 

Resistance to weathering. Zinc oxide and magnesium oxide stabilize poly-chloroprene against dehydrochlorination. Further, zinc oxide helps vulcanize the rubber, and magnesium oxide reacts with /-butyl phenolic resin to produce a resinate which improves heat resistance of solvent-borne polychloroprene adhesives. 

J.-I. Lee, G. Klaemer, and R.D. Miller, Oxidative stability and its effect on the photoluminescence of poly(fluorene) derivatives end group effects, Chem. Mater., 11 1083-1088, 1999. 

Poly(organosiloxane)s have a number of outstanding properties such as thermal and oxidative stability, water and chemical resistance, electric insulating capacity, selective permeability to gases, and biocompatibility. 

Of all the hydrocarbon-based PEMs, this group most likely has the largest variety of different systems. This is probably due to the wealth of prior knowledge of the nonsulfonated analogues that have been developed over the last several decades as well as the general expectation of higher thermal stability, better mechanical properties, and increased oxidative stability over polystyrene-based systems. Within the context of this section, polyarylenes are systems in which an aryl or heteroaryl ring is part of the main chain of the polymer. This section will, therefore, include polymers such as sulfonated poly (ether ether ketone) and sulfonated poly(imides) but will not include systems such as sulfonated polystyrene, which will be covered in Section 3.3.I.3. 

Although Parylene-N possesses an outstanding combination of physical, electrical, and chemical properties, the benzylic C—H bonds present are potential sites for thermal and oxidative degradation. It is well known that replacing a C— bond with a C—F bond not only enhances the thermal stability of the resulting polymer, but also reduces the dielectric constant. Because incorporation of fluorine is known to impart thermal and oxidative stability, it became of interest to prepare poly(a,a,a, a -tetrafluoro- p -xylylene), Parylene-F Joesten reported that the decomposition temperature of poly(tetrafluoro-j9-xylylene) is ca. 530°C. Thus, it seemed that the fluorinated analog would satisfy many of the exacting requirements for utility as an on-chip dielectric medium. 

Other high performance polymer backbones have been explored as PEM materials in addition to poly-(arylene ether)s and polyimides. Ductile copolymers with high modulus and glass transition values are desirable PEM candidates. The hydrolytic and oxidative stability of many of these materials remains to be determined. Nevertheless, interesting synthetic methodologies have been employed to investigate these materials, which have been instructive in the search for new PEM candidates. 

Poly(arylene ether)s generally exhibit high glass transition temperatures, resistance to hydrolysis, as well as an excellent thermo-oxidative stability. 

Throughout this chapter the chemical concepts employed to synthesize and cure addition poly(imides) have been discussed and their use as matrix resins for fiber composites has frequently been mentioned. The most important property of the imide backbone structure is the inherent thermal stability. The target of achieving the temperature performance of linear poly(imide) has not been reached, because of the aliphatic nature of the reactive endgroups, and because of the low molecular weight of the imide backbone required for processing. Future developments of addition polyimides will, as in the past, focus on the requirement of high thermal and thermal oxidative stability of the crosslinked... 

Poly[2,2 -(m-phenylene-5,5 -benzimidazole)] (PBI) is a very high glass transition temperature (Tg 430°C), commercially available material. It possesses excellent mechanical properties, but is difficult to process into large parts and has high moisture regain and poor thermo-oxidative stability at temperatures above approximately 260 °C. Polyimides, especially the thermoplastic polyimides, offer attractive thermo-oxidative stability and processibility, but often lack the thermal and mechanical characteristics necessary to perform in applications such as the matrix for high use-temperature (over 300 °C) structural composites (for example, carbon fiber reinforced) for aerospace use. The attempt to mitigate... 

Siloxane elastomers present an attractive alternative to the butadiene acrylonitrile elastomers most often used for epoxy modification. Poly(dimethyl siloxanes) exhibit glass transition temperatures well below those of butadiene acrylonitrile modifiers (minimum —123 °C vs. about —40 °C) and also display very good thermal stability13, 14). Other favorable and potentially useful attributes include good weatherability, oxidative stability, and moisture resistance. Finally, the non-polar nature and low surface energy of poly(dimethyl siloxanes) constitute a thermodynamic driving force... 

T50I(NPG)/PMDA was of particular interest because of its adhesive characteristics, oxidative stability, and polymer cost. Table III shows the improvement in adhesion obtained when various substrates were coated with blends containing this polyester (acid number 39). As indicated in the table, the ease of obtaining adhesion on the different substrates decreased approximately in the following order brass > steel > copper > chrome-coated steel > aluminum > nylon 66 > poly (ethylene terephthalate). In spite of the wide differences in structure and polarity of the various polymers, the carboxylated polyester significantly improved the adhesion of the coatings. 

Oxidation Stability (OSI or Rancimat) has been introduced in many ways. In EN14214 it exists as OSI and as a maximum acceptable Iodine Value, or maximum level of linolenic acid or of poly-unsaturated fatty acids. Oxidation stability is of importance when it comes to polymerization and oxidation during storage as well as during use in the engine. Oxidation is directly related to the presence of unsaturated bonds in the FAME, and probably because of this the EN 14214 includes a cap on Iodine Value. 

Poly-unsaturated (PUFA) methyl esters have a much lower oxidation stability than mono-unsaturated (MUFA) or saturated (SAFA) methyl esters,... 

TABLE 1. Physical and oxidative stability of poly(silarylene-siloxane-acetylene) elastomers after isothermal curing. 

Poly p-phenylene (104) was expected to have good thermal and oxidative stability as well as electrical conductivity in the oxidized or reduced states. Rehahn et al. reported the first cross-coupling reaction of dihaloarenes 100 and aryldiboronic acids (101) to provide poly (p-phenylenes) (104) [160]. Homologation was achieved via repeating the following sequence of reactions lithiation, boration, and Suzuki coupling [160]. 

In addition to the elastomers already described, others, have been produced on an experimental scale. These include the perfluoroalkylenetriazines with their unsurpassed thermal oxidative stability for an elastomer but with many offsetting disadvantages, and poly(thiocarbonyl fluoride). It is probably true to say that material does not have any outstanding desirable property that cannot now be matched by an alternative and commercially available material. 

Metal oxide semiconductor chemical sensors in combination with MDA have been shown to be useful to estimate the oxidative stability of polypropylene during processing instead of traditional melt flow index analysis (50). An array of sensors was used to receive a detailed analysis of volatiles. At quality measurements of different poly(butylene adipate)s the use of indicator products has been proven better than analyses of the decrease in molecular weight or mass loss for early degradation detection. Adipic acid, quantified using gas chromatography, was then used as the indicator product [51]. 

Hydrolytic Stability. The polymers exhibited not only thermal oxidative stability, but also good hydrolytic stability. The hydrolytic stabilities of these polymers in the form of films and varnished wire were evaluated in water and aqueous base. The electrical resistance of th<=ge films ( 0 1.5 mm, 0.035-0.040 mm thick) in boiling water was 10 ohms. After treating in water at 200 C for 30 hours, the electrical resistances and weights of PPT (I)-PPT (V) remained essentially unchanged whereas the film of poly-imide suffered a 9.43% weight loss and failed to be an insulating material under the same condition. In order to make further observation on hydrolytic stability, a varnished wire was made by... 

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