Stabilizing action

Emulsion Polymerization. When the U.S. supply of natural mbber from the Far East was cut off in World War II, the emulsion polymerization process was developed to produce synthetic mbber. In this complex process, the organic monomer is emulsified with soap in an aqueous continuous phase. Because of the much smaller (<0.1 jira) dispersed particles than in suspension polymerization and the stabilizing action of the soap, a proper emulsion is stable, so agitation is not as critical. In classical emulsion polymerization, a water-soluble initiator is used. This, together with the small particle size, gives rise to very different kinetics (6,21—23). 

Finally, some general rules for the amount of surfactant appear to be vaHd (13). For anionic surfactants the average size of droplets is reduced for an increase of surfactant concentration up to the critical micellization concentration, whereas for nonionic surfactants a reduction occurs also for concentrations in excess of this value. The latter case may reflect the solubiHty of the nonionic surfactant in both phases, causing a reduction of interfacial tension at higher concentrations, or may reflect the stabilizing action of the micelles per se. 

The introduction of Hquid crystals as stabilizing elements for emulsions occurred in 1969 when it was found that the sudden stabilization at emulsifier concentrations in excess of 2.5% of a water—% xylene emulsion by a commercial octa(ethylene glycol) nonylphenyl ether was due to the formation of a Hquid crystalline phase in the emulsion (26). Later investigations confirmed the strong stabilizing action of these stmctures (27). 

The UV stabilizing action of nickel and iron complexes (e.g., NiDRC and FeDRC) is strongly concentra-... 

Irg 1076, AO-3 (CB), are used in combination with metal dithiolates, e.g., NiDEC, AO-30 (PD), due to the sensitized photoxidation of dithiolates by the oxidation products of phenols, particularly stilbenequinones (SQ, see reaction 9C) (Table 3). Hindered piperidines exhibit a complex behavior when present in combination with other antioxidants and stabilizers they have to be oxidized initially to the corresponding nitroxyl radical before becoming effective. Consequently, both CB-D and PD antioxidants, which remove alkyl peroxyl radicals and hydroperoxides, respectively, antagonise the UV stabilizing action of this class of compounds (e.g.. Table 3, NiDEC 4- Tin 770). However, since the hindered piperidines themselves are neither melt- nor heat-stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. 

Flecainide (Tambocor) and propafenone (Rythmol) are examples of class I-C drags. These drugs have a direct stabilizing action on the myocardium, decreasing the height and rate of rise of cardiac action potentials, thus slowing conduction in all parts of the heart. 

The formation of a weakly basic tertiary amine in reaction 4.102 does not alter the titrant normality, but in the titration of an acid it may suppress the height of the titration curve on the basic side. In an extensive study of twelve quaternary ammonium titrants in non-aqueous media (mainly isopropyl alcohol), Harlow73 observed large differences in stability the presence of water had a profound stabilizing action but at the sacrifice of basic strength inert and basic solvents increased the rate of decomposition (see Fig. 4.18). 

If simple proportional control works fine (in the sense of acceptable offset), we may try PD control. Similarly, we may try PID on top of PI control. The additional stabilizing action allows us to use a larger proportional gain and obtain a faster system response. 

The importance of thermally stable char was shown to be critical in a further study of siloxane block polymers by General Electric researchers. (18). The char enhancing action of magnesium soaps and a special silicate silane (19) and likewise the char stabilizing action of lead salts (20) were demonstrated in polyolefins by General Electric investigators. 

The short bulky aromatic compound does not pack well in a lamellar liquid crystalline structure, the mutual stabilizing action of the straight hydrocarbon chains is lost, and instability results. 

Pharmacology Propafenone is a Class 1C antiarrhythmic with local anesthetic effects and direct stabilizing action on myocardial membranes. 

Because the p-receptors of the heart are primarily of the pi type and those in the pulmonary and vascular smooth muscle are p2 receptors, Pi-selective antagonists are frequently referred to as cardioselective blockers. The intrinsic activity, cardioselectivity, and membrane-stabilizing actions of a number of p-blockers are summarized in Table 11.2... 

D. At high pre-pressures, dilution becomes more important. It more or less neutralizes the effect of penetration by the hot gases, exerts a stabilizing action, and at 1000 atm, assumes the dominant role... 

It was shown by the above authors that nitrogen content of nitric esters such as NG or NC cannot be determined by the nitrometer method, if stabilizers such as centralite are present, because centralite absorbs some nitrogen oxides thus giving a low result for N. The difference between the nitrometer N content of NG in absence of a stabilizer and N content of NG in presence of a stabilizer may be taken as an index of stabilizing action of the stabilizer the bigger the difference, the better the stabilizer. This difference is called indice nitrometrique... 

Local anesthetic action, also known as "membrane-stabilizing" action, is a prominent effect of several 3 blockers (Table 10-2). This action is the result of typical local anesthetic blockade of sodium channels (see Chapter 26) and can be demonstrated experimentally in isolated neurons, heart muscle, and skeletal muscle membrane. However, it is unlikely that this effect is important after systemic administration of these drugs, since the concentration in plasma usually achieved by these routes is too low for the anesthetic effects to be evident. These membrane-stabilizing 3 blockers are not used topically on the eye, where local anesthesia of the cornea would be highly undesirable. Sotalol is a nonselective 3-receptor antagonist that lacks local anesthetic action but has marked class III antiarrhythmic effects, reflecting potassium channel blockade (see Chapter 14). 

The experiments summarized in Table 175 show the stabilizing action of nitro-naphthalene. Dinitro- and trinitronaphthalene also act in a stabilizing manner. On the other hand mixed nitramines such as tetryl are detrimental to stability. 

Ballistites initially consisted of equal amounts by weight of nitroglycerine and soluble nitrocellulose CP2 with the addition of aniline or diphenylamine as stabilizers. It was found, however, that the presence of aniline and diphenylamine is detrimental to the stability of the powder, and they were therefore omitted. The valuable properties of centralite as a solvent of low basicity were then recognized and it was used both for its ability to dissolve the nitrocellulose and for its stabilizing action. 

Dalbert (Ref 18) examined the stabilizing action of DPhA in Poudre B (see Vol 2 of Encycl, p B 1-L) and also made comparison (after storage for 16 months at 50°) of a doublebase proplnt stabilized with 8.75% Centralite with two other proplnts in which 2% of Centr was replaced with either DPhA or Carbazole. Results of tests showed that Centralite alone was a better stabilizer than its mixts with DPhA Crbz... 

However, the complete elimination of the radicals is problematic, because their stability and hence their lifespan is enhanced by various kinetic or thermodynamic effects. For instance, alkyl groups have a stabilizing action and there is also a steric intervention by substituents with a blocking action or reduced mobility owing to strong crosslinking. Thus, some radicals hardly have any opportunity for recombination and remain isolated in the matrix. 

HUMECANIS AND MOISTURE-RETAINING AGENTS. Substances lhal have affinity for water, with stabilizing action on the water content of a material, are culled htimertants or moisture-retaining agents. Ideally, a... 

Nathan et al(Ref 1) examined a number of carbamic acid esters and concluded that the best stabilizing action on NC is obtd with compds in which at least one H atom is replaced by an aryl radical. Davis(Refs 2 5) examined several comps for their gelatinizing effect on NC Refs 1)F.L.Nathan et ai, BritP 12743(1912) CA 7, 3842(1913) 2)T.L.Davis, IEC 14, 1140 (1922) 3)Franklin(1935), lllff 4)Sidgewick, OrgChem of N(1937), 272 5)Davis(1943), 322... 

W.R.Ashford et al, CanJRes 24B, 238- 45 (1946)(Stabilizing action of ethanol on starch... 

Central ite 1 Analytical Procedures. Centr 1 can be detected by various colorimetric tests, such as described in Refs 1,6,12,24, 28 Sc 33. Some other qualitative tests are given in Ref 13. Quantitative detns of Centr 1 by bromination methods are described in Refs 4,5,7,9,10,14,16,17,20,27,34 Sc 35. Chromatographic and spectrophotometric methods are found in Refs-11,15,18,21,22,23,24, 29,30,32 Sc 33. Other quantitative methods, including polarographic, are in Refs 2,7a,20a,25, 26,27 Sc 30. X-ray diffraction spectra data are given in Ref 19. Detns of stabilizing action of Centr 1 by methods of Taliani and Thomas are discussed in Refs 3 8... 

Aging of proplnts contg Centr 1, its stabilizing action on NC NG,and transformation products formed during aging are discussed in Refs 1-7 9-10. Nitro compds of Centr 1, some of them formed during aging of proplnts, are described here under Centralite 1, Nitro Derivatives of... 

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