Insoluble additives

In order to obtain a homogenous and stable latex compound, it is necessary that insoluble additives be reduced in particle size to an optimum of ca 5 )Tm and dispersed or emulsified in water. Larger-size chemical particles form a nucleus for agglomeration of smaller particles and cause localized dispersion instabiHty particles <3 fim tend to cluster with similar effect, and over-milled zinc oxide dispersions are particularly prone to this. Water-soluble ingredients, including some accelerators, can be added directly to the latex but should be made at dilute strength and at similar pH value to that of the latex concentrate. 

Blending of ABS with an acrylic material such as poly(methyl methacrylate) can in some cases allow a matching of the refractive indices of the rubbery and glassy phases and providing that there is a low level of contaminating material such as soap and an absence of insoluble additives a reasonable transparent ABS-type polymer may be obtained. More sophisticated are the complex terpolymers and blends of the MBS type considered below. Seldom used on their own, they are primarily of use as impact modifiers for unplasticised PVC. 

In the case of nanoencapsulations of solids, or the incorporation of high molecular weight, highly water-insoluble additives (such as polymers, oligomers, alkyds) into polymer particles, macroemulsion polymerization will not work, since the high molecular weight material will remain in the monomer droplet as the monomer is transported out. At the end of the reaction, the additive will remain in the depleted monomer droplets, rather than in the polymer particles. Clearly, these products can only be made via miniemulsion polymerization. 

The catalysts comprise a chelating ligand such as diphenylphosphinobenzoic or-acetic acid combined with nickel sources like (j) -l,5-cyclooctadiene)2Ni (equation 18) or NiCl2/NaBH4. A nickel hydride species is presumed to be the active catalytic species. On an industrial scale, the reaction is run in a polar solvent such as 1,4-butanediol, in which the catalyst is soluble but the olefin products are insoluble. Addition of B(C6F5)3 to these systems converts them from neutral to zwitterionic see Zwitterion) with a large increase in activity (equation 19). ... 

Bianchini, R. Resciniti, M. Vecchio, C. Technological evaluation of aqueous enteric coating systems with and without insoluble additives. Drug Dev. Ind. Pharm. 1991, 77(13), 1779-1794. 

Use Determination of cholesterol (an insoluble addition compound is formed), analytical reagent. 

Parenthetically, many pharmaceuticals—in fact, most of them—contain "insoluble" additives. If you are a chronic user of any medication, prescription or over-the-counter, you are a candidate for Crohn s disease. The doctors at the University of London who did the polystyrene experiments concluded "Perhaps we should be more concerned about the fate of insoluble materials in toothpaste and pharmaceuticals which might be taken chronically." Another British group at St. Bartholomew s Hospital has added corroborating evidence by discovering aluminum, silicon, and titanium in the lesions of Crohn s disease. 

Silicone-based oil-insoluble additives are incorporated at extremely low dosage to control any tendency to form stable foam. It is important that they are dispersed throughout the oil and within an appropriate particle size range, achieved using a high-shear stirrer. 

Recrystallization of a small sample from EtOH dropped this to 179-181 deg C. This salt was treated with 30 mL 5% NaOH, and the red solution decanted from some insolubles. Additional H20 and NaOH effectively dissolved everything, and the resulting basic aqueous phase was extracted with 3x50 mL CH2CI2. The pooled extracts were stripped of solvent under vacuum, and the residue dissolved in 200 mL anhydrous Et20 and saturated with anhydrous HCI gas. There was a heavy precipitation of white crystals, which were removed by filtration,... 

The motivation for stating point (4) arises from the fact that many so-called homogeneous catalytic reactions are acmally present in multiphase slurries and these slurries arise, for example, and, in some cases, due to the addition of various insoluble additives or auxiliaries or the formation of precipitates. For the present chapter, point (4) explicitly excludes surface-mediated reaction steps in the homogeneous catalytic reaction mechanism. 

Finally, it is worth mentioning that PVA cryogels are able to incorporate different soluble and insoluble additives inside the pores to obtain composite materials of both scientific and applied interest [4—6]. In particular, PVA-based cryogels have been obtained that include inside the porous structure nanoparticles of solid crystalline compounds, co-elastic gels, microorganisms, gas bubbles, or microdroplets of liquids immiscible with PVA solutions [4—6, 92-98]. 

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