Oligomers characterized

Mutter, M., Renard, C. M., Beldman, G., Schols, H. A., and Voragen, A. G., Mode of action of RG-hydrolase and RG-lyase toward rhamnogalacturonan oligomers. Characterization of degradation products using RG-rhamnohydrolase and RG-galacturonohydrolase. Carbohydr Res 1998, 311 (3), 155-64. 

Acetylenic molecules undergo oligomerization in the cavities of acidic zeolites, giving rise to carbocationic oligomers characterized by intense colors. It has been argued that the mechanism of the reaction can be represented by the scheme shown in Fig. 2b, which, in the case of acetylene, becomes that shown in Scheme 4 (152). 

Synthesis of these oligomers and the requisite endcapping agent is given below. Oligomer characterization and preliminary cure studies are also described. 

Jannie P. J. Marais studied at the University of the Free State, Bloemfontein, South Africa where he obtained his Ph.D. in organic chemistry in 2002. His research focused on characterization of the free phenolic profile of South African red wine, and the stereoselective synthesis of flavonoids, for example, flavan-3,4-diols and flavanones. He joined the National Center for Natural Products Research at the University of Mississippi as a postdoctoral associate in July of 2002, where he worked with Dr. Ferreira on the stereoselective synthesis of flavonoid precursors, the semi-synthesis of proanthocyanidin oligomers, characterization of proanthocyanidin profiles of selected transgenic plants, and the synthesis of radioactive antimalarial 8-aminoquinolines. He was promoted to associate research scientist in 2005, where his main area of research still remains the synthesis of A- and B-type proanthocyanidins, starting at the monomeric level and continuing through the tri- and tetra-meric, to the deca-mer level. 

The value for the heat of fusion of PPS, extrapolated to a hypothetical 100% crystalline state, is not agreed upon in the literature. Reported values range from approximately 80 J/g (19 cal/g) (36,96,101) to 146 J/g (35 cal/g) (102), with one intermediate value of 105 J/g (25 cal/g) (20). The lower value, 80 J/g, was originally measured by thermal analysis and then correlated with a measure of crystallinity deterrnined by x-ray diffraction (36). The value of 146 J/g was deterrnined independendy on uniaxiaHy oriented PPS film samples by thermal analysis, density measurement via density-gradient column, and the use of a calculated density for 100% crystalline PPS to arrive at a heat of fusion for 100% crystalline PPS (102). The value of 105 J/g was obtained by measuring the heats of fusion of weU-characterized linear oligomers of PPS and extrapolation to infinite molecular weight. 

Prior to the development of analytical techniques to quantify specific methylene urea oligomers, methylene urea polymer distributions were characterized by physical (solubihty) methods. Products were separated into three fractions (3). 

The structure of the products were characterized by two detector gel-chromatography (recractometer and UV). The direction of the alkylation reaction of toluene with EC was changed depending on the reaction condition as follows if the ratio of toluene-EC is 1 5 mol, the alkylation reaction is toward obtaining the PEC at 273 K and if the ratio is reverse at 333 K, the reaction undergone to obtain epoxy toluene oligomer is shown in Fig. 1. 

The polaron is characterized by the reversal of bond alternation, which, in the case of polythiophene, extends over five monomer units [30-32], and the appearance of two localized stales in the band gap ). These states have been indeed observed by UV-V1S absorption of both oligomers and polymers, in solution [33— 40] and in the solid state [41-45]. 

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