Solvent type

Polyoxymethylene is obtained as a finely divided soHd. The bulk density of the product, which is very important for ease of handling in subsequent manufacturing steps, is influenced by many reaction variables, including solvent type, polymerisation temperature, and agitation. 

The molecular weight of a polymer can be controlled through the use of a chain-transfer agent, as well as by initiator concentration and type, monomer concentration, and solvent type and temperature. Chlorinated aUphatic compounds and thiols are particularly effective chain-transfer agents used for regulating the molecular weight of acryUc polymers (94). Chain-transfer constants (C at 60°C) for some typical agents for poly(methyl acrylate) are as follows (87) ... 

Solution Polymers. Methacryhc solution polymers are usually characterized by thek composition, soHds content, viscosity, molecular weight, glass-transition temperature, and solvent type. The compositions of methacryhc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—Hquid chromatography, and refractive index measurements. The soHds content is determined by dilution followed by solvent evaporation to constant weight. Solution viscosities are most conveniendy determined with a Brookfield viscometer. Methods for estimating molecular weights by intrinsic viscosity are available (103). 

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

Physical solvent type Fluor solvents (propylene carbonate example), Selexol Physical/chemical type Sulfinol Carbonate type Potassium carbonate Solution batch type Lo-Cat, Chemsweet Bed batch type Iron Sponge, Mol Sieve... 

Observable Characteristics - Physical State (as normally shipped) Liquid Color. Colorless Odor Mild, pleasant aromatic, solvent-type. 

The lrialkyl(trifluorovmyl)slannanes were used in the Pd(0)-catalyzed coupling reaction of aryl halides [77] (equation 12). The product yield increased with the solvent type in the order hexamethylphosphorus triamide (HMPT) DMF > dimethyl sulfoxide (DMSO) > tetrahydrofuran (THF) > CgHg > C2H4CI2. 

The perfluoroarylcopper reagents react with perfluoroalkylated acid fluorides to give ketones in excellent yields. Solvent, type of organometallic reagent,... 

OBJECTIVE To pump a specified solvent type to the required blender... 

In the maintenance of exterior timber, the surface application of creosote or a decorative solvent-type preservative at suitable intervals adds greatly to service life. 

For the remedial treatment of fungal decay and insect attack on timber in buildings, clear solvent-type preservatives applied by spraying all available surfaces are generally used, supplemented with wood preservative pastes to obtain deep penetration. Water-based emulsions are also used for woodworm control. There has been a general move towards the use of those... 

The values of k" and E are highly dependent on the initiator types and their effects on the solvent types are less overwhelming. The types of solvent used as chain transfer agent are usually fixed... 

Gelatins are classified according to whether an acid or an alkali is used in the final preextraction step. If an acid solution is used as the final solvent, type-A gelatin (acid process) is obtained. In case of alkali as the final solvent, type-B gelatin (alkali process) is obtained. Type-A gelatin s isoelectric point is higher compared to that of type-B gelatin, as a... 

Galvanic cells of the Nerst type are also termed cells with dissolution membranes or solvent type membranes [3]. Such systems are defined by the distribution equilibria in which all ions, present in aqueous and in organic solvents, participate (Section III.A). The general examples of the liquid concentration and chemical galvanic cells of this type are presented in the form of Schemes 8 and 9. 

Organic solvent can affect the enzyme specificity [76]. Authors have indicated that transesterification of l,4-butyloxy-2-octylbenzene and butanol in presence of lipases from Pseudomonas can produce two different products when using hydrophilic (acetonitrile) or hydrophobic (toluene) solvents. Zaks and Klibanov [16], demonstrated that subtilisine and a-chymotrypsine specificites can be changed as a function of solvent types. This is true for a limited number of biocatalysts. 

From our previous treatment of the Arrhenius, Bransted and Lewis acid-base theories, the importance of the choice between the divergent solvent types clearly appeared if we now confine ourselves to solvents to which the proton theory in general is applicable, this leads to a classification of eight classes as already proposed by Bronsted35,36 (Table 4.3). 

---