Paramagnetism, poly

Bi-Sr-Ca-Fe-CuOx, having a paramagnetic phase, exhibited catalytic activity in the dehydration of tert-BuOH to isobutylene, another ceramic superconductor Bi-Sr-Co-Fe-CuO having a diamagnetic phase, inhibited the reaction. The paramagnetic poly(aniline disulfide), when used as a modifier for LaHY Zeolite (20%)-Al2O3 ( %) catalysts for the cyclohexane isomerization at 350 °C, increased the selectivity for methylcyclopentane and methylcyclopen-tenes [194],... 

Recently, Lipton et al. [25] have used zinc-67 NMR to investigate [Zn(HB(3,5-(CH3)2pz)3)2] complexes which have been doped with traces of paramagnetic [Fe(HB(3,4,5-(CH3)3pz)3)2]. The low-temperature Boltzmann enhanced cross polarization between XH and 67Zn has shown that the paramagnetic iron(II) dopant reduces the proton spin-lattice relaxation time, Tj, of the zinc complexes without changing the proton spin-lattice relaxation time in the Tip rotating time frame. This approach and the resulting structural information has proven very useful in the study of various four-coordinate and six-coordinate zinc(II) poly(pyrazolyl)borate complexes that are useful as enzymatic models. 

Two different kinetic approaches have been used to obtain mechanistic information [15,16]. Kinetic studies carried out by EPR spectroscopy using fusinite as a paramagnetic probe of the oxygen concentration allowed the oxidizability of poly(hydrosilane)s to be obtained [15]. Oxidizability values of 1.8 x 10 and... 

Effects of temperature and paramagnetic additives on the spectrum of poly(dichlorophenyleneoxide). The spectra of the polymers referred to in Figure 1 were all measured up to 120° in tetrachloroethylene. In no case did any significant change occur in the spectrum on heating. 

Sulfur nitride polymers [-(-S = N-)-], which have optical and electrical properties similar to those of metals, were first synthesized in 1910. These crystalline polymers, which are super-conducive at 0.25 K, may be produced at room temperature using the solid state polymerization of the dimer (S2N2). A dark blue-black amorphous paramagnetic form of poly(sulfur nitride) (structure 11.30) is produced by quenching the gaseous tetramer in liquid nitrogen. The polymer is produced on heating the tetramer to about 300°C. 

Poly(acrylic acid) (PAA) with an average molecular weight of 250,000 was used to coat a dry tablet of ZnS Mn, which was obtained by compressing the powder at 173 MPa. The amount and state of doped manganous ion, Mn(II), was examined by electron paramagnetic resonance spectroscopy (EPR). EPR enables us to gather various extra information with respect to the state of Mn(II). 

Poly (methyl methacrylate) was also subjected to mechanical reaction in a vibrating mill in common solvent for several monomers (ethylene, acrylic acid and its esters, acrylonitrile and styrene) at temperatures from —196 to 20° C (22). The formation of macroradicals and their reactions were followed by EPR (electron paramagnetic resonance). The macroradicals reacted with vinyl monomers at temperatures less than —100° C, while quinones underwent reaction as low as —196° C. The same experiments were performed also with polystyrene and polybutylenedimethacrylate. The radicals from polystyrene were more reactive than those from poly(methyl methacrylate). 

The amount of radicals in carbon black filled rubbers decreases significantly upon extraction of free rubber with the aid of a solvent containing a free radical scavenger. The extraction nevertheless causes a substantial increase in the fraction of the T2 relaxation component with the decay time of about 0.02-0.03 ms [62], This increase is apparently caused by an increase in the total rubber-carbon black interfacial area per volume unit of the rubber due to the removal of free rubber. The T2 relaxation component with a short decay time is also observed in poly(dimethyl siloxane) (PDMS) filled with fumed silicas [88], whose particles contain a minor amount of paramagnetic impurities. Apparently, free radicals hardly influence the interpretation of NMR data obtained for carbon-black rubbers in any drastic way [62, 79]. 

After photolysis at room temperature of the degassed aqueous solutions of colloidal Ti02 (anatase, 2R = 10-15 run) in the presence of poly(vinyl alcohol) (PVA), EPR spectra recorded at 77 K showed existence of several types of paramagnetic centers in the system... 

However, disorder appears to be crucial in the occurrence of photoexcited paramagnetic centers since irradiation of single crystal samples, e.g. poly TS, has no effect. The energy levels in the low energy absorption tail of the disordered samples play an important part. It is not clear if these derive from excitonic or interband transitions but it should be noted that in principle any distortion of the polymer chain can lead to defect states in the optical gap ( ) and that the weak absorption tail in crystals is a major factor determining photoconduction (9 ). Thus, it appears that a basis exists for the correlation of structure and the intrinsic absorption spectra but that further efforts are required to obtain a better understanding of defect states and their spectroscopic properties. 

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