Effect of Additives and Impurities

When the emulsion polymerization of St was carried out in the presence of Fremy s salt and ammonium peroxodisulfate in the aqueous phase, a distinct 

Okaya et al. [240] investigated the effect of additives such as alcohol (isopropyl alcohol) on the initial stage of the emulsion polymerization of MMA 0 wt%) initiated by APS in the presence of PVA (1%). They found that 90% of MMA and 60% PVA were grafted and that stable polymer particles with an 

---

Amongst the factors that will influence service performance are the effect of additives and impurities, temperature, detailed geometric size and shape, orientation and morphology, surface condition, energy and speed of any impacting blow, the shape of the impacting instrument, the environment, and strains in the article due to external loads. For this reason it is desirable, but not always feasible, to test prototype articles under conditions as close to service conditions as possible. 

Results obtained by the GPC and DSC studies are in excellent agreement. Correlations between GPC and DSC data provide a better understanding of epoxy resin cure behavior and are useful In assessing the effects of stoichiometry and impurities. Simple amine-to-epoxy addition is the predominant reaction between TGMDA and DDS during the early stages of cure. This reaction is adeguately described by a third-order rate expression (Eg. 10). 

The earlier discussion on the effects of additives or impurities on crystal growth (Section 11.3.2) suggests that impurity incorporation is often surface specific. Black and Davey (1988) have reviewed much of the available information on the crystallization of amino acids. Amino acids are interesting model systems because of their common zwitterion group coupled with a variety of side chains, which may be present on a particular crystal face. L-asparagine can accommodate some 15% of L-aspartie acid as a mixed crystal (solid solution). From the effects of aspartic acid on the habit of asparagine crystals it is believed that aspartic acid primarily is incorporated at the 010 face whose growth rate is considerably reduced. 

The work discussed in the previous paragraphs provides the framework for the prediction of crystal habit from internal structure. The challenge is to add realistic methods for the calculation of solvent and impurities effects on the attachment energies (hence the crystal habits) to allow this method to provide prediction of crystal habit. Initial attempts of including solvent effects have been recently described (71. 721. The combination of prediction of crystal habit from attachment energies (including solvent and impurity effects) and the development of tailor made additives (based on structural properties) hold promise that practical routine control and prediction of crystal habit in realistic industrial situations could eventually become a reality. 

The organic additives have been employed to counteract the harmful effects of different metallic impurities. Such additives act by increasing the induction period, by complexing the harmful impurities, or by suppressing the hydrogen evolution reaction. The additives also increase the current efficiency, reduce the power consumption, and improve the surface morphology. 

The influence of impurities on electrochemiluminescence emission behavior has been difficult to ascertain. The best quantum yield of emission under annihilative conditions thus far achieved is about 1 %.63 The preannihilative emission is one to two orders of magnitude less intense.11 As the concentration of fluorescer in emitting systems is ca. 10 3M, as low a concentration of impurity as 10 7M may be responsible for the entire emission. Investigations thus far conducted have tacitly accepted such impurity levels in these solutions and have concentrated on inferring their action by observing the effects of additives... 

In one study of the effects of additives,9 it was found that on electrochemical oxidation of rubrene, emission was seen in dimethylforma-mide, but not in acetonitrile. When water, n-butylamine, triethylamine, or dimethylformamide was added to the rubrene solution in acetonitrile, emission could be detected on simply generating the rubrene cation.9 This seems to imply that this emission involves some donor or donor function present in all but the uncontaminated acetonitrile system. The solvent is not the only source of impurity. Rubrene, which has been most extensively employed for these emission studies, is usually found in an impure condition. Because of its relative insolubility and its tendency to undergo reaction when subjected to certain purification procedures, and because the impurities are electroinactive and have relatively weak ultraviolet absorptions, their presence has apparently been overlooked, They became evident, however, when quantitative spectroscopic work was attempted.70 It was found, for example, that the molar extinction coefficient of rubrene in benzene at 528 mjj. rose from 11,344 in an apparently pure commercial sample to 11,980 (> 5% increase) after repeated further recrystallizations. In addition, weak absorption bands at 287 and 367 m, previously present in rubrene spectra, disappeared. 

Effect of Water and Divalent Metal Ions on the Electronic Structure of DNA. As a first step in investigating the effect of impurities on the electronic structure of DNA, the band structure of poly(G-C) was computed in the PPP CO approximation assuming that one or two water molecules are bound by hydrogen bonds to the NH2 group of each C molecule or/and to the 0=0 group of each G molecule.94 According to the results obtained for these systems the additional 7r-orbital in the H20 molecules produced an extra 71-band between the lowest filled bands, while the other bands remained practically unchanged. 

Transfer processes can be caused by monomer, counterion, and other components of the reaction mixture (additives, solvents, impurities). The latter reactions are sometimes called spontaneous because they are zero order in monomer. However, the spontaneous elimination of /3-protons is very unlikely, and proton elimination must be assisted by some basic reagent. The ratio of the rate constants of /8-proton elimination to that of electrophilic addition depends on several factors. The relative rate of transfer decreases with temperature, and therefore polymers with higher molecular weights are formed at sufficiently low temperatures. The effect of solvent and counterion is not yet sufficiently understood. 

Effects of additives, impurities, and pH on the crystai habit, crystai size distribution, crystai purity, and crystal hardness. 

Fillers. Fillers are added in epoxy formulations to obtain the desired properties in a system. Additionally, they reduce the cost of formulations. The amount of filler by weight that can be incorporated into an epoxy resin will depend on the filler s particle size, density and oil absorption properties. Within each family of filler there are products that impart different properties because of varying coarseness, impurity level and method of preparation. The effect of addition of fillers to epoxy formulations is to ... 

Winyl polymerization as a rule is sensitive to a number of reaction variables, notably temperature, initiator concentration, monomer concentration, and concentration of additives or impurities of high activity in chain transfer or inhibition. In detailed studies of a vinyl polymerization reaction, especially in the case of development of a practical process suitable for production, it is often desirable to isolate the several variables involved and ascertain the effect of each. This is difficult with the conventional batch polymerization technique, because the temperature variations due to the highly exothermic nature of vinyl polymerization frequently overshadow the effect of other variables. In a continuous polymerization process, on the other hand, the reaction can be carried out under very closely controlled conditions. The effect of an individual variable can be established accurately. In addition, compared to a batch process, a continuous process normally gives a much greater throughput per unit volume of reactor capacity and usually requires less labor. 

For a given polymeric structure, the morphology (crystallinity and orientation), formulation (additives, fillers and impurities), humidity (especially for polar polymers), temperature, and pressure, are the most important factors which affect the thennal conductivity. References [1-8] review many of these factors. In addition, see Bigg [14] and Ross et al [15] for detailed treatments of the effects of fillers and of pressure, respectively, on thermal conductivity. 

The effect of addition of ferric stearate to polyethylene was studied (76), and a large ESR spectrum was observed after irradiation at —196° C, although the spectral shape was different from that of polyethylene itself. These results could be expected according to the mechanism of radical formation from metal impurities, as mentioned before. 

---