Polymerization precipitation

Oxidation first produces soluble oxygenated compounds of molecular weights between 500 and 3000 that increase the viscosity of oil then they polymerize, precipitate, and form deposits. Oxidation also causes formation of low molecular weight organic acids which are very corrosive to metals. 

The addition of a cyclic vinyl sulfoxide anion to aldehydes has been reported only once14. Interestingly, 2,3,4,5-tetrahydro-l//-thiepane S-oxide cannot be metalated by lithium diiso-propylamide in tetrahydrofuran at — 78 °C. At higher temperatures ( — 20° to 0°) a white polymeric precipitate is formed. This polymeric product is also formed when the sulfoxide is treated with butyllithium or. wr-butyllithium in tetrahydrofuran even at — 78 C. However, metalation can be accomplished with. sec-butyllithium using an excess of N,N,N, N -tetramcthylethylenediamine in tetrahydrofuran at —78 C. In this case, a pale yellow solution is formed immediately and upon addition of benzaldehydc instantaneous dccolorization occurs yielding a mixture of diastereomeric alcohols in 90% yield. 

The radical intermediates "P can couple with each other, leading to the formation of polymeric precipitates that can be readily removed from water (see Figure 17.2). The polymerization of the free radicals is known to be extremely fast, and it is therefore not included in the above reaction scheme. 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

Polymeric beads obtained via emulsion polymerization, precipitation, etc. can be stained with dyes providing that both have functional groups available [7]. Covalent coupling is mostly preferred but the attachment based on strong electrostatic interactions is also feasible. This method is mostly used to design pH- and ion-sensitive micro- and nanobeads. The dynamic response of such systems can be... 

Heterogeneous polymerization is used extensively to control the thermal and viscosity problems. There are three types of heterogeneous polymerization precipitation, suspension, and emulsion. Emulsion polymerization is discussed in Chap. 4. Precipitation polymerizations begin... 

The initial rate of polymerization versus base molar concentration ratio of template to monomer shows a sharp maximum in the range of [T]/[M] = 1.5. Polymerization was initiated by AIBN and UV light at 365 nm. Poly(dimethylaminoethyl methacrylate) with polyCacrylic acid) give a complex. During polymerization, precipitation takes place. From the product obtained, the daughter polymer and the template were isolated by dissolving the complex in 10% NaCl solution, addition of proper amount of NaOH, followed by dialysis. 

Emulsion polymerization a sufficient amount of dispersing agent and mild agitation is employed. This produces small colloidal particles dispersed in the aqueous reaction medium. In this procedure, called aqueous dispersion polymerization, precipitation of the resin particles is avoided. The coagulated dispersion produced by emulsion polymerization is often called a fine-powder or PTFE dispersion. 

With regard to a solubility equilibrium, the fact that vitreous silica behaves like a precipitate of polymeric silicic acid must be caused by the similarity between polymeric silicic acid and the hydrated surface of vitreous silica. Both forms can release silicic acid by hydrolysis and desorption, and likewise both forms are able to adsorb and condense silicic acid by means of silanol groups randomly distributed on their surfaces. Thus, in order to explain equal final states, the only assumption necessary is that the condensates will not attain the degree of dehydration of the bulk of the vitreous silica. The resulting equilibrium then relates to the two-phase system silicic acid—polymeric precipitate, and strictly speaking, this system is in a supersaturated state with respect to vitreous silica, which can be considered as an aged form of silica gel. 

The copolymer produced during the polymerization precipitated as a white powder, soluble in DMF, chloroform, and liquid S02. Elementary analysis proved the exact alternating composition irrespective of monomer feed ratio. On heating, they decomposed at 220°-230°C without melting. 

Any colloidal material provides an intrinsically favorable accessibility to its surface when compared to bulk material. Therefore, the availability of receptor binding sites should be facilitated by using colloidal MIPs. Submicron scale MIPs were prepared by precipitation polymerization, emulsion polymerization, and miniemulsion polymerization. Precipitation polymerization uses the insolubility of the formed polymer microgel in a certain solvent, whereas emulsion and miniemulsion polymerization employ two solvent phases for the preparation of the colloidal polymer. The latter methods offer the opportunity for tailoring the surface of the colloids exclusively, thereby enhancing the accessibility of the binding sites. Each of the three approaches has their own characteristics and will be described in the following sections. 

Plant material is well known for its contents of tannins and various phenolic compounds that may polymerize-precipitate on the surface. It is... 

In solvents of high dielectric constant, (e.g. dimethylformamide), formaldehyde polymerized sluggishly and polymers were formed in low yield. In similar solvents, aliphatic aldehydes could not be polymerized. Precipitated aldehyde polymers have the tendency to absorb monomers. The monomer concentration near the propagating site may be much hi er than that in the surrounding solution. This occurs with n-butyraldehyde polymerizations in pentane [5] the polymer precipitated during the polymerization is highly swollen by the monomer. 

These values of physico-chemical parameters confirm a high surface activity of precipitated active aluminium hydroxide. Both a number of active sites and a well-developed specific surface area are considerably greater for polymeric precipitants than for aluminium oxides. 

FIGURE 2.7 With the free interface diffusion method illustrated schematically here, the protein sample, in buffer, is simply layered, with care, atop the precipitant solution, which may be either salt or polyethylene glycol. Salt ions diffuse rapidly into the protein solution aided by convective transport, and local concentration gradients are created in the region of the interface. With polymeric precipitants, both the polymer and the protein diffuse into one another, but at a greatly reduced rate. 

Gel Formation, Entrapment of enzymes in solid matrices composed of synthetic or natural polymers or inorganic gels is a relatively simple process. The basic technique involves occlusion of the enzyme within the lattice of a solid matrix as the matrix is formed by polymerization, precipitation, or coacervation. Gels... 

The modeling of heterogeneous polymerization systems is generally more complicated than that of the homogenous systems because mass and heat transfer effects between two or more immiscible phases must be considered. Industrially important heterogeneous polymerization reactions include emulsion polymerization, suspension polymerization, precipitation polymerization, and solid-catalyzed olefin polymerization. The general polymerization rate equation is represented simply as... 

Transition metal catalyzed, ring opening polymerization Dispersion, cationic polymerization Homogeneous/precipitation, cationic polymerization Homogeneous, free radical/cationic polymerization Precipitation, free radical polymerization Dispersion, free radical polymerization Norbornene polymer, polycarbonate Isobutylene polymer Vinyl ether polymer Amorphous fluoropolymers Vinyl polymer, semicrystalline fluoropolymers Polyvinyl acetate and ethylene vinyl acetate copol5Tner... 

MTO hydrolyzes rapidly in basic aqueous solutions and much more slowly in acidic media. At low concentrations (crMT0 < 0.008 M) the formation of methane gas and perrhenate is detected. The decomposition of MTO seems to be irreversible. At higher concentrations a second reaction, a faster reversible polymerization -precipitation, takes place to yield a golden-colored solid of the empirical composition H05[(CH3)092Re03] (poly-MTO) in about 70% yield (Eq. 1) [10-15]. 

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