Polymer formation reduction

Temperature control at -15° to -25°C was also required for maximum yield. The best results were obtained by maintaining a temperature of -20 to -25°C during the addition of citral anil to the acid and at -15°C for the duration of the reaction. At this temperature range, the formation of a-cyclocitral (III) is favored. Higher temperatures caused excessive polymer formation and favored formation of e-cyclocitral whereas lower temperatures caused a reduction 1n the yield of the citral mixture. At least part of the problem with the lower temperature reaction was the fact that the sulfuric acid tended to freeze around the inside of the reaction vessel causing the effective molar ratio of acid to anil to be reduced. These lower temperature reaction mixtures were also lighter in color which indicated less polymer formation but this was accompanied by a lower yield of cyclocitrals. 

A general strategy developed for the synthesis of supramolecular block copolymers involves the preparation of macromolecular chains end-capped with a 2,2 6/,2//-terpyridine ligand which can be selectively complexed with RUCI3. Under these conditions only the mono-complex between the ter-pyridine group and Ru(III) is formed. Subsequent reaction with another 2,2 6/,2"-terpyridine terminated polymer under reductive conditions for the transformation of Ru(III) to Ru(II) leads to the formation of supramolecular block copolymers. Using this methodology the copolymer with PEO and PS blocks was prepared (Scheme 42) [ 107]. 

The aqueous chemistry of molybdenum and tungsten is complicated by polymer formation in acid solution and reduction potential data are not known with certainty. The acid-solution chemistry of molybdenum is summarized in Table 7.17. 

Other carboxylate-dye interactions have been reported. Ethylenediamine tetracarboxylic acid (EDTA) and its salts are well known reductants for a variety of dyes (54,55). The amino-acid N-phenylglycine can be photooxidized and induce polymer formation (26,56,57). Studies of the efficiency of photopolymerization of acrylate monomers by MB/N-phenylglycine combinations as a function of the pH of the medium suggest that either the amino group or the free carboxylate can act as an electron donor for the dye excited state, but that the amine functional-lity is the more efficient coinitiator (10). Davidson and coworkers (58) have shown that ketocarboxylic acids are photode-carboxylated by electron transfer quenching of dye triplet states under anaerobic conditions. Superoxide formation can occur when oxygen is present. 

Electrochemical synthesis of various cyclic alkylsilanes has been performed similarly113. It should be noted that 5-silaspiro[4,4]nonane is formed despite the high probability of polymer formation due to the high functionality of the silicon. Such high selectivity in the electrochemical ring closure seems to be due to the orientating effect of an electrode in the course of an irreversible reduction of a carbon-halogen bond in the monosilylated intermediate (equations 87 and 88). 

Aldehyde-tannin and aldehyde-anthocyanin condensation reactions result in polymer formation (Figure 1). These polymers may be responsible for haze formation in wine and the polymers may eventually precipitate out of solution (26). The polymerized tannins have different flavor properties than the monomeric starting units (21-29) and formation of anthocyanin polymers affects wine color. In addition, these reactions may result in a reduction of aldehyde flavors in the wine. These condensation reactions are discussed more fully in other chapters of this volume. The formation of strong covalent bonds between the aldehyde and the tannin or anthocyanin makes recovery of the bound aldehydes difficult. 

Increasing the concentration of catalyst brings about a reduction in the time to the exothermic peak. The exothermic peak temperature increases as the percentage of catalyst is increased. This increase in temperature is due to the autoacceleration effect that occurs when the viscosity of the monomer-polymer solution increases very rapidly with polymer formation. The percentage of conversion is approximately constant, except for a drop at the 1.2% and 1.5% vazo... 

As in the case of emulsion polymerization, an increase in the functional monomer concentration leads to a reduction in the hnal hydrodynamic particle size and enhanced water-solnble polymer formation, as illustrated in Fignres 12.14 and 12.15 for batch polymerization of (NIP-MAM/MBA/IDA/KPS). The rednction in particle size vs. functional monomer has been attribnted to the enhancement of precnrsor formation and the number of stable particles which rapidly become the polymerization loci. 

Plutonium reduction. Reduction of plutonium to Pu(III) is completed by adding concentrated hydroxylamine (with hydrazine as holding reductant) to the aqueous raffinate leaving the HC column. The mixture must be held long enough, half an hour or more [B2], to complete the rather slow reduction to Pu(III). To hasten the reaction, the hydroxylamine concentration should be high and the nitric acid concentration as close to 0.3 M as possible without risking plutonium polymer formation. 

Polymer formation within different points of a reaction zone (therefore, at different temperatures) results in a reduction of the MW and broadening of the MWD, comparing the most probable value ... 

There is by far less information available on the cathode interface than the anode interface. However, the reports appeared recently, which insisted that there is a film on the cathode, which may be called a SFI as well as the anode." Since the oxidative reactions on the cathode cannot immobilize reaction products like the reductive reactions on the anode, the amount of SFI on the cathode is much smaller than that on the anode, as demonstrated in Fig. 4.11. Due to the analytical difficulties, a very few data in the literature report the effects of electrolyte additives on the cathode. It was reported that the addition of VC reduced the interfacial impedance and improved a bit the rate capability. It was speculated that this effect is caused by the polymer formation by VC on the cathode, which suppresses the deposition of lithium fluoride, since this effect disappeared when VC contained polymerization inhibitors such as BHT. This is reasonable because the oxidation potential of VC is lower than those of other carbonate solvents. ... 

Garnish and Haskins found that exposure of polypropylene to trichloroethylene vapour for 10 s resulted in a sixfold increase in joint strength using an Epoxide adhesives. The authors concluded that the improved adhesion was due to the removal of a weak boundary layer. However, the treatment causes the formation of a very porous surface, and an alternative explanation for the improved adhesion is the mechanical keying of the adhesive into the porous surface (see Mechanical theory of adhesion). Garnish and Haskins found that the optimum treatment time was about 10 s and that after 25 s the adhesion level was similar to that of the untreated polymer. This reduction is probably due to weakening of the surface region of the polypropylene. 

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