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11.
Reactivity ratios for the copolymerization of styrene (r 1) meta-divinylben-zene (r 2–m) and with para-divinylbenzene (r 2–p) have been redetermined under different reaction conditions and with different radioactivity assay techniques. The copolymers were prepared at two conversion levels [0.55 to 3.7% and 2.7 to 7.5% and at 80° (rather than 100°)] with benzoyl peroxide (in place of τ-butylhydroperoxide) initiator. The ionization chamber-vibrating reed electrometer radioactivity assay technique developed for other copolymerization studies was used in place of the direct counting technique previously used for the styrene/divinylbenzene systems. The new values are r 1 = 0.605/r 2-m = 0.88: r 1 = 0.77/r 2-p = 2.08 at 0.55 to 3.7% conversion and r 1 = 1.27; r 2–m = 1.08 at 2.7 to 7.5% conversion. These are not in close agreement with previous values partly because of the difference in conditions of copolymerization (temperature, per cent conversion, initiator) and in the improved analytical precision. Also the high-DVB-content (80%) para copolymer data are not assumed to be invalid and are not omitted (as they were before) from selection of the r 2–p values. 相似文献
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Abstract The rate of sulfonation of bead copolymers of styrene cross-linked with 8 mole % divinylbenzene (mixed isomers) is remarkably sensitive to the isomeric (para/meta) composition of the mixture of divinylbenzenes. The rate is enhanced by a factor of 4 for compositions containing 20–40% para isomer. 相似文献
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Solvent-modified (toluene) copolymers have been prepared from styrene cross-linked with commercial divinylbenzene, m-divinylbenzene, and p-divinylbenzene at divinyl monomer contents of 16 mole % and 32 mole % at FM = 0.50. The resultant copolymers have been characterized by swelling-ratio determinations and rates of sulfonation at 60 and 80°C. The solvent-modified 16 mole % cross-linked copolymers sulfonated at rates slightly greater than those characterizing the 8 mole % cross-linked copolymers prepared in the absence of diluent. The order of decreasing sulfonation rates for both the conventional 8 mole % cross-linked systems and for the solvent-modified 16 mole % cross-linked copolymers is commercial divinylbenzene/styrene, p-divinylbenzene/styrene, m-divinylbenzene styrene. The 32 mole % cross-linked systems exhibit a different order of decreasing sulfonation rates: commercial divinylbenzene/styrene, m-divinylbenzene/styrene, p-divinylbenzene/styrene. The swelling ratios of the 32 mole % solvent-modified copolymers were comparable to those of the conventional 8 mole % cross-linked systems. 相似文献
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Viciu L Caruntu G Royant N Koenig J Zhou WL Kodenkandath TA Wiley JB 《Inorganic chemistry》2002,41(13):3385-3388
A new series of transition-metal oxyhalides (MCl)LaNb(2)O(7) (M = Cr, Mn, Fe, Co) have been prepared by a simple topochemical route. Layered perovskite hosts (ALaNb(2)O(7), A = Li, Na, K or Rb) were reacted with the corresponding anhydrous metal halides under mild reaction conditions (<400 degrees C). The compounds were examined by X-ray powder diffraction; the series appears to be isostructural with (CuCl)LaNb(2)O(7), and the layer spacings, with the exception of M = Co, follow the trend expected from transition-metal cationic radii. Thermal analysis with differential scanning calorimetry (DSC) shows the materials to be metastable where all four compounds decompose exothermically above 690 degrees C. 相似文献
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H. W. Wiley 《Fresenius' Journal of Analytical Chemistry》1894,33(1):586-587
Ohne Zusammenfassung 相似文献
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Paul R. Challen David B. McConville Wiley J. Youngs 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):310-311
The title compound, Na(C24H20P)[V(C7H6OS)2O], contains oxovanadium(IV) in a square‐pyramidal coordination geometry with a basal plane consisting of a cis‐S2O2 donor group. The [VO(mmp)2]2? (mmpH2 = 2‐mercapto‐4‐methylphenol) units are linked into infinite chains by the sodium ions. 相似文献