Color oligomers

Equilibrium in the highly acidic media during chlorination of sulfuretin also involved 23 (Fig. 9.3.5). Treatment of 23 with chlorine dioxide affords ortho-quinone (24) (Fig. 9.3.6), which is further subjected to successive acid-catalyzed condensation via the dimer (25) to the colored oligomer (26), the final speck substance (Fig. 9.3.6) (119). 

The mechanism of formation of chromophores in the oligomeric fraction of the polymer is uncertain. It is possible that oligomers decompose to form chromophores or that the polymer unzips or slits off colored oligomers from the high polymer. 

It has been found [648] that such route of N-vinylpyrroles hydrolysis can be realized only in the dilute solutions if the released acetaldehyde is coupled (e.g., by the reaction with hydroxylamine). Under normal conditions, however, complex acid-catalyzed and oxidative condensation reactions of the initial and formed pyrroles with acetaldehyde as well as between pyrroles themselves take place. Consequently, mixtures of deeply colored oligomers, the composition of which depends on the hydrolysis and isolation conditions, are formed. On the basis of the literature data [1,2,627], spectral (IR, NMR, and ESR) characteristics, and the results of elementary analysis, it has been assumed [648] that these mixtures contain fragments A-D (Scheme 2.189). 

We have demonstrated a new class of effective, recoverable thermormorphic CCT catalysts capable of producing colorless methacrylate oligomers with narrow polydispersity and low molecular weight. For controlled radical polymerization of simple alkyl methacrylates, the use of multiple polyethylene tails of moderate molecular weight (700 Da) gave the best balance of color control and catalyst activity. Porphyrin-derived thermomorphic catalysts met the criteria of easy separation from product resin and low catalyst loss per batch, but were too expensive for commercial implementation. However, the polyethylene-supported cobalt phthalocyanine complex is more economically viable due to its greater ease of synthesis. 

FIGURE 3.11 (See color insert following page 336.) Optically active F -oligomer unit, built from eight optically inactive (W)-3.15 monomers. The calculated spectra of this octamer is in accordance with both the experimental VIS and CD spectra. (Reprinted from Foss, B.J. et al., Chem. Eur. J., 11, 4103, 2005b. With... 

FIGURE 17.19 2D contour plot of a modified polyamide 6, first dimension LCCC, second dimension SEC. Area 1 unmodified chains, area 2 modified chains, area 3 cyclic oligomers. (See color plate.)... 

Y Yoshida, N Tanigaki, K Yase, and S Hotta, Color-tunable highly polarized emissions from uniaxially aligned thin films of thiophene/phenylene co-oligomers, Adv. Mater., 12 1587-1591, 2000. 

Siloxane compounds, in vitreous silica manufacture, 22 414 Siloxane materials, 20 240 Siloxane oligomers, in silicone polymerization, 22 555-556 Siloxanols, silylation and, 22 703 Silsesquioxane hybrids, 13 549 Silsesquioxanes, 15 188, 22 589-590 SilvaGas process, 3 696, 697 Silver (Ag), 22 636-667. See also Silver compounds. See Ag entries Argentothiosulfate complexes Batch desilverizing Lead-silver alloys Palladium-silver alloy membranes analytical methods for, 22 650-651 applications of, 22 636-637, 657-662 as bactericide, 22 656, 657, 660 barium alloys with, 3 344 in bimetallic monetary system, 22 647-648 in cast dental gold alloys, 8 307t coke formation on, 5 266 colloidal precipitation color, 7 343t colloidal suspensions, 7 275 color, 7 334, 335... 

Fig. 37 a Schematic diagram that illustrates the equilibrium shifting driven by folding and ligand binding. The sequences are color coded, b Chemical structure of oligomers used in the metathesis reaction... 

Cured BCB/BMI specimens are a transparent golden brown in color, similar to what was seen for the BCB oligomer. Once the specimens have been removed from the mold they are postcured for 1 hour at 300 C in nitrogen resulting in an extent-of-cure of greater than 95X. 

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