Oxidative stability Linear poly

Aliphatic polybenzimidazoles were first synthesized by scientists in the 1950s. However, it was not until the 1960s that H. Vogel and C.S. Marvel first synthesized aromatic polybenzimidazoles and discovered that these unique, highly stable linear heterocyclic rigid-rod polymers exhibited exceptional thermal and oxidative stability [65]. Poly[2,2 -(m-phenylene)-5,5 -bibenzimidazole], PBI, was prepared by the condensation polymerization of... 

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... 

This chapter describes our recent advances on the utilization of polymer-modified laccase complexes in aqueous systems towards the oxidation/polymerization of naturally hydro-phobic steroidal compounds, Equilin (EQ) and 17-P-estradiol (P-EST). We elucidate the kinetic and synthetic aspects of the process with the model compoimd 5,6,7,8-tetrahydro-2-naphthol (THN). The nano-reactor system is composed of linear poly(ethylene oxide)-dendritic poly(benzyl ether) diblock copolymer (G3-PE013k) and laccase isolated from Trametes versicolor. Other advantages of the complex in comparison to the native enzyme are its recyclability, enhanced stability, activity, and overall simplicity in product harvesting and isolation. A principle of action of the complex is suggested based on these findings and is further supported by the biphasic solid-liquid nature of the reaction medium, which exhibits continuous influx of starting material and steady solid product expulsion. Comparative experiments with linear-linear poly(styrene)-Woc -poly(ethylene oxide) copolymer under identical conditions do not evince formation of a... 

Schauer J, Brozova L. Heterogeneous ion-exchange membranes based on sulfonated poly(l,4-phenylene sulfide) and linear polyethylene preparation, oxidation stability, methanol permeability and electrochemical properties. J Membr Sci 2005 250(l-2) 151-7. 

The reason they are called "ladder" polymers is because they may be considered derivatives of poly(acene), whose structure (Fig. 14-23) is characterized by two linear sideframes with interconnecting "rung" bonds, very much like that of a ladder. For our purposes, they do qualify as CPs, since they are possess a 7r-conjugated polymeric structure, and can indeed also be doped for greatly increased conductivity. The interest in these polymers has been due to their greater thermal and oxidative stability as compared to more conventional CPs, their facile processibility in their... 

High temperature thermosets and ceramics have been synthesized by heat treatment of various blends of poly (siloxane-acetylene) and poly (carborane-siloxane-acetylene). The polymeric blends give high char yields on pyrolysis, and the resultant chars show excellent oxidative stability to at least 1500 °C. The thermosets and ceramic chars show similar oxidative stability to previously studied copolymers containing varying amounts of siloxane, carborane, and acetylene units within the backbone. It has been determined that only a small percentage of carborane is necessary to provide this oxidation protection. Thus, these precursor linear hybrid polymers are more cost-effective than previous polymers which contained carborane in each repeating unit. 

The major advantage of our approach is that the desirable features of inorganics and organics such as high thermal and oxidative stability and processability are incorporated into the same polymeric chain. The siloxane units provide thermal and chain flexibility to polymeric materials. Siloxane-acetylenic polymers have also been made but lack the thermal and oxidative stability that the carborane units possess. The chemistry involved in synthesizing poly(siloxane) and poly(carborane-siloxane) has been modified to accommodate the inclusion of an acetylenic unit in the backbone. The novel linear... 

Surfactants for urethane and related polymer foams are usually silicone-surfactants. These surfactants generally are copolymers of poly(dimethylsiloxane) [-Si(CH3)2-0-] , oxyalkylene chains, e.g., polyethylene oxide chain (EO) , and polypropyene oxide chains, (PO) . The copolymers can be linear, branched or pendant types. The surfactants have different functions, i.e., emulsifying, foam stabilizing, and cell-size control. 

This peak potential also fits the linear correlation established between pola-rographic oxidation half-wave potentials for substituted aromatic compounds and their ionization potentials [161]. It should be noted that the radical cation of 66 may be either a 7r-delocalized or S,S 2c, 3e o species. Compound 67 shows a reversible first oxidation potential in acetonitrile with E1/2=0.87 V vs SCE [162]. Perylene derivative 68 exhibits a first oxidation peak in nitrobenzene at 0.65 V vs Ag/AgCl [163]. Because of the good thermal stability and high electrical conductivity of the radical cation of 68 [164], functionalized analogues have also been prepared and studied [165]. Poly(alkylthio)pyracyclene has been studied [166]. 

Data have been published dealing with successful applications of HAS in stabilization of other polymers than PO elastomers, styrenic polymers, polyamides, polycarbonates, polyacetals, polyurethanes, linear polyesters, thermoplastic polyester elastomers, polyacrylates, epoxy resins, poly(phenylene oxide) or polysulfide [12]. In spite of their basicity, HAS may also be used for stabilization of PVC. This application includes less basic derivatives of piperidine and 1,4-dihydropyridine [12,13,145,146]. 

The initial steps in oxidative reaction of aromatic, poly-aromatic and other cyclic and linear unsaturated hydrocarbons in the atmosphere or in combustion involve radical formation. These radicals react with molecular oxygen. The subsequent reactions of these peroxy radicals, as shown e.g. in Figure 4.1, result in unsaturated linear or cyclic, oxygenated or multi-oxygenated hydrocarbon intermediates. The thermochemistry for these unsaturated - oxygenated species is needed to evaluate their stability and likely reaction paths in the environment, in combustion and in other thermal and oxidative processes. 

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