Yellowing, polymers

Fifteen grams of this prepolymer powder in a wide-bore reaction tube (Fig. 3.18b) which is flushed with nitrogen is placed in a heating block. The heating block is warmed over a period of 1 h to 270°C and maintained at this temperature for 4 h, after which the reaction vessel is removed. The yellow polymer obtained has an r]i h of 1.9. The polymer has a melting temperature of 391°C, a heat of fusion of 148 J/g, a Tg dry at 120°C, and a Tg wet at —15°C. 

A reactor containing 10 ml of toluene and 10 ml of aqueous Na2C03 was treated with the step 2 product (1.0 mmol), 2,7-dipinacol boron-9,9-di-octyl-fluoiene (1.0 mmol), tetrakis triphenylphosphine palladium (0.01 mmol), and 0.16 ml of tricaprylmethyl-ammonium chloride. The mixture was then treated with a few drops of bromobenzene and then refluxed for 1 hour and treated with a few drop of phenyl boronic acid and then further refluxed 15 hours and cooled. The mixture was diluted with toluene and isolated toluene layer washed with water. The mixture was filtered after adding 40 mg of the palladium scavenger 3-mercaptopropyl modified silica gel. The solution was then poured into methanol and a yellow polymer isolated. The polymer was redissolved in toluene and then purified using a short column of silica gel. The solution was rewashed with water, reprecipitated in ethanol, and 0.80 g of polymer isolated having an Mn of 32,800 Da. 

Primary alkyl isocyanides are known not to comply simply to homopolymerization. It was recently reported that polyisocyanides prepared with nickel(II) compounds varied in color from yellow to black (22,23). The latter occurred at preparative temperatures in excess of 25° C, or when polymer non-solvents or acids were used. Further, the addition of acids to solutions or suspensions of the yellow polymers also led to black compounds. The NMR spectrum of a soluble polymer sample (i.e. MVPO = 1100) of black poly(ethyl isocyanide) shows methylene resonance shifts to values as occur in nitriles, which were interpreted as giving evidence of rearrangement to a polycyanide... 

Victrex (PES) and Radel (PAS) serve the same end uses and are, like Udel, transparent, slightly yellow polymers exhibiting heat deflection temperatures about 28°C higher than Udel PSO. Their main advantage in electrical and electronic end use is high heat resistance. They also have excellent water and chemical resistance like all polysulfones they are steam sterilizable. Electrical and electronic end uses represent the largest market segment. Applications include connectors, switches, bobbins, and sleeves. 

Unfortunately there seems to be no supplementary evidence on copolymerization initiated by phosphines. In a typical experiment, a solution of acrylonitrile in petroleum ether is treated with a little triethyl phosphine. A greenish-brown product settles on the walls of the flask. It is soluble in acetone, furfural, methyl ethyl ketone and DMF. Polymer precipitated from acetone by toluene is of low molecular weight and contains perhaps 0.5% combined phosphorus. In similar experiments it is possible to obtain pale yellow polymers with number average molecular weights of around 30,000 and with about one atom of P per polymer chain. On the basis of these results Horner and coworkers proposed the scheme (72) ... 

From an experimental viewpoint the polymerization of 6.19, where R and R are both methyl groups, takes place in the bulk (molten) phase in sealed glass tubes at 130 °C and the reactions are complete in less than one hour. The yellow polymer is formed in almost quantitative yield and is soluble in solvents such as THF. The molecular weight is in the range of 3 x 105 to 5 x 105 (1,300-2,000 repeating units). 

Later Schwarz and coworkers580, 582, 584) reported the formation of higher chlorosilanes and of a yellow polymer chloride (SiCl) 579 in the pyrolysis of SiCl4. The polymer is an amorphous yellow powder, stable up to 400 °C, but sensitive to water. On average, three valencies of every silicon atom are bonded to silicon while the fourth valence is occupied by a chlorine atom. The exact 1 1 ratio of Si Cl is surprising, since a variety of compositions would be expected. 

The alkyls and aryls may be obtained by interaction of copper(I) halides with lithium or Grignard reagents. The alkyls usually decompose readily but methyl copper, a bright yellow polymer insoluble in organic solvents, is reasonably stable it can be used in certain organic syntheses, but the use of lithium alkyl cuprates... 

Tl(rV), V(IV), In(III) led to the polychelates (125M), (126M). If the degree of polycondensation is not too high, the yellow polymer ligands are soluble in polar solvents. The intensively coloured polychelates are insoluble. 

Analogous ochre-yellow polymers 145 that contain thiophene in the main chain 11,300-35,300, PDI = 1.5-2.7)... 

An analogous synthetic approach that uses Ni(0)-catalyzed dehalogenative polycondensation. yielded, for example, yellow polymers 151 with = 8,000-13,600 and PDI = 1.3-2.1 by GPC (Equation (54)). " Comparison of the UV-VIS spectrum for the polymer with that for the model dimer was consistent with the presence of a... 

Typical catalysts for the polymerization of phenylacetylene contain W, Rh and Fe. W catalysts produce an auburn polymer WCl6-P Sn is highly active, while W(CO)6-CCl4-hv is useful to achieve high molecular weight (Mn 1 x 10 ). The polymerization by Rh catalysts proceeds in alcohols and amines to form a yellow polymer When... 

It is known that Mo catalysts give cis-rich yellow polymers, while W catalysts provide trans-rich, auburn polymers. ... 

CH2CHCOOEt WCl6/EtAlCl2/80°C 72% yield, M = 8500, yellow polymer Gal 1995c... 

The presence of hydrocarbons invariably leads to a brownish-yellow polymer deposit on the plasma walls. Laser action (X. = 337 pm) is observed in tubes containing this type of deposit if the discharge is maintained in pure H2, H2O or NH3. Schoetzau and Vepfek have explained the experimentally observed gain of HCN lasers in terms of the combined effects of volume processes and wall reactions — the latter include the formation of excited HCN by the reaction of H atoms with the deposit formed by discharge-activated polymerization of hydrocarbons in the laser tube. 

Peroxyseleninic acids. Treatment of a mercurated 2%-crosslinked polystyrene with selenium dioxide affords a yellow polymer (Equation 6) which has been assigned the structure of polymer-bound phenylseleninic acid (32). 

Analogous ochre-yellow polymers 4.26 that contain thiophene in the main chain (Mw= 11,300-35,300 PDI = 1.5-2.7) have also been prepared [61]. Upon slow concentration of their solutions in chlorinated solvents, such as chloroform, lyotropic nematic liquid-crystalline phases form. In one case, a lyotropic smectic state was identified. 

Acrylonitrile is readily soluble in water, whereas poly(acrylonitrile) is not. The polymerization, therefore, is a precipitation polymerization in aqueous solution with K2S2O8 as free radical source. In alkaline media, yellow polymers, which presumably contain some imine structures, are obtained these structures are formed by the polymerization via the nitrile groups, or the N-oxide groups formed by subsequent oxidation ... 

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