Spherical polymeric particles

The above work was extended by Ranade and Mashelkar [47] by considering the dissolution of a spherical polymeric particle in a convective field. The transport equations written were very similar to the ones used by Devotta et al. [46]. In addition, the solvent velocity, Ui, was given as... 

Values calculated for the force of adhesion of spherical polymeric particles to a steel surface, with allowance for deformation of the surfaces in accordance with Eq. (11.75), have been compared with experimental data [66] ... 

Suspension and emulsion polymerization are two classical polymerization techniques to produce spherical polymeric particles. Larger particles (usually larger than 50 tim) with an appreciable size distribution are produced by suspension polymerization. Submicron polymeric particles (usually smaller than 0.1 im) with extremely uniform in size are obtained by conventional emulsion polymerization processes. Recent techniques, such as swollen emulsion polymerization, dispersion polymerization, etc. give micron-size (usually between 1-50 im) monosize polymeric particles (23). 

Emulsion—Suspension Polymerized Pigment Ink. Polymerization of a polar prepolymer as the internal phase in an oil-based external phase (24) gives a fluorescent ink base in which spherical fluorescent particles are dispersed. This base is suitable for Htho and letterpress inks (qv). An... 

The polymerization applied produces spherical polymer particles (1-10 pm diameter) connected by polymer bridges [3]. Thus, a one-piece polymer phase is obtained. The interstices between the particles have a characteristic length of a few micrometers. Overall, the polymer structure can be ascribed as lose. 

An aqueous colloidal polymeric dispersion by definition is a two-phase system comprised of a disperse phase and a dispersion medium. The disperse phase consists of spherical polymer particles, usually with an average diameter of 200-300 nm. According to their method of preparation, aqueous colloidal polymer dispersions can be divided into two categories (true) latices and pseudolatices. True latices are prepared by controlled polymerization of emulsified monomer droplets in aqueous solutions, whereas pseudolatices are prepared starting from already polymerized macromolecules using different emulsification techniques. 

In 1994, we reported the dispersion polymerization of MM A in supercritical C02 [103]. This work represents the first successful dispersion polymerization of a lipophilic monomer in a supercritical fluid continuous phase. In these experiments, we took advantage of the amphiphilic nature of the homopolymer PFOA to effect the polymerization of MMA to high conversions (>90%) and high degrees of polymerization (> 3000) in supercritical C02. These polymerizations were conducted in C02 at 65 °C and 207 bar, and AIBN or a fluorinated derivative of AIBN were employed as the initiators. The results from the AIBN initiated polymerizations are shown in Table 3. The spherical polymer particles which resulted from these dispersion polymerizations were isolated by simply venting the C02 from the reaction mixture. Scanning electron microscopy showed that the product consisted of spheres in the pm size range with a narrow particle size distribution (see Fig. 7). In contrast, reactions which were performed in the absence of PFOA resulted in relatively low conversion and molar masses. Moreover, the polymer which resulted from these precipitation... 

The aerosol technique can also be used to produce polymer colloids by addition polymerization. Thus, when droplets of toluene-2,4-diisocyanate (TD1) or 1,6-hexa-methylene diisocyanate (HDI) were brought into contact with ethylenediamine (EDA) vapor (in the apparatus shown in Fig. 1.5.3) spherical polyurea particles with modal diameters of 1-3 p,m were formed. The entire process, i.e., the formation of droplets and the polymerization, was carried out at moderate temperatures (<80°C)... 

The most common support is highly pure, spherical, microporous particles of silica that are permeable to solvent and have a surface area of several hundred square meters per gram (Figure 25-5). Most silica should not be used above pH 8, because it dissolves in base. Special grades of silica are stable up to pH 9 or 10. For separation of basic compounds at pH 8-12, polymeric supports such as polystyrene (Figure 26-1) can be used. Stationary phase is covalently attached to the polymer. 

Furthermore, Fu et al.140 developed a transport system that responds to thermal stimuli. This system is based on chains of poly-iV-isopropylacrylamide (a known thermosensitive polymer), which exists in a collapsed, hydrophobic state when exposed to heat, but in an expanded, hydrophilic state in the cold. In this way, samples of mesoporous, spherical silica particles (particle diameter 10 p,m) that were lined and coated with the thermosensitive polymer by atom transfer radical polymerization... 

The similar, older slurry process uses a less active catalyst. The monomer is dissolved in isooctane, the titanium catalyst and aluminium cocatalyst are added and this mixture is fed to the reactor which is maintained at 70°C. The inorganic corrosive (Cl) residues are removed in a washing step with alcohols. The atactic material is removed by extraction. A third process employs propene as the liquid in combination with a high activity catalyst. The Himont Spheripol process, which uses spherical catalyst particles, gives spherical polymer beads of millimetre size that need no extrusion for certain purposes. A more recent development is the gas-phase polymerization using an agitated bed. All processes are continuous processes, where the product is continuously removed from the reactor. Over the years we have seen a reduction of the number of process steps. The process costs are very low nowadays, propene feed costs amounting to more than 60% of the total cost. 

Polymerization in microemulsion has developed into a powerful technique for the preparation of strictly spherical micronetworks [1,2]. The final size of the polymerized particles is solely governed by the ratio of surfactant to monomer concentration, i.e., the fleet ratio S. To predict the final particle size at full conversion, two simple models for the polymerization in microemulsion have been proposed which differ only in some minor details. One of the models considers variable headgroup contributions to the particle radius [3]. This calculation finally arrives at Eq. 1. 

Polyacetylene latexes (48) have been prepared by polymerizing acetylene in the presence of poly[(fert-butylstyrene)-fo-(ethylene oxide)]. The use of a tetrahydrofuran/cyclohexane (THF/cyclohexane) solvent combination led to the formation of a stable dispersion of nearly uniform spherical polyacetylene particles 40-200 nm in diameter. The block copolymer was separated from the polyacetylene by several wash cycles with a good solvent for the block copolymer (cyclohexane), and after removing the solvent, a polyacetylene powder was obtained. On the basis of nitrogen adsorption... 

A serious problem in the control of silica polymerization is that, in general, initial particle formation is a result of random bond formation between a range of polysilicate species in solution. Moreover, the aggregation process is uncontrolled under conventional preparation conditions. It is important to understand the basic mechanisms of particle formation and aggregation in aqueous solution, as the physical properties of such silicas are determined primarily by the coordination number and nature and strength of interactions between essentially spherical primary particles. 

Reverse micellar systems were used for the polymerization of phenol derivatives. HRP-catalyzed polymerization of p-ethylphenol in the ternary system composed of a bis(2-ethylhexyl) sodium sulfosuccinate (AOT)—water—isooctane system produced spherical polyphenol particles having 0.1—2 /tm diameters quantitatively.21 Similar particles were obtained by pouring the solution of enzymatically prepared polyphenol into a nonsolvent containing AOT.22... 

For chromatographic applications, monodisperse spherical MIP particles are preferable to the irregularly shaped MIP particles formed by grinding and sieving the polymer monoliths. Consequently, some researchers have developed methods that produce spherical MIP particles through precipitation polymerization and emulsion polymerization. Monodisperse MIP microspheres were prepared by Mosbach et al. under similar conditions to the MIP monolith preparation but under significantly more dilute precipitation polymerization conditions. The MIP microspheres grew to 1-3 pm diameter with a narrow size distribution. 

These imprinted micro spheres can then be packed more efficiently into chromatography columns or into solid-phase extraction (SPE) cartridges than the particles prepared by bulk polymerization techniques. Larger spherical imprinted polymer particles can be prepared by modification of preformed latex particles either by reswelling with a secondary polymerization mixture or by coating a spherical core particle with an imprinted polymer shell. 

The polyethylene latexes obtained in the different emulsion polymerization procedures using the various aforementioned nickel(II) complexes display average particle diameters of 100 to 600 nm. A number of anionic surfactants or neutral stabilizers are suitable, i.e. compatible with the catalysts and capable of stabilizing the latex. Solids contents of up to 30% have been reported to date. A typical TEM image is shown in Fig. 7.2. By comparison to smooth, spherical latex particles of amorphous polystyrene as a well studied hydrocarbon polymer prepared by free-radical emulsion polymerization, the ruggedness of the particles shown can be rationalized by their high degree of crystallinity. 

The particles in the air over an urban area are of a variety of sizes, shapes and chemical composition, ranging from tiny, spherical metal particles from metallurgical fumes to huge, porous conglomerates of sooty carbon, soil particles, fly ash, and fly dust of all types.The size and shape of the particles will almost totally determine the surface corrosion of polymers, plastics, the polymer in paints and lacquers. The important question is how these particles behave in the air, how far and how fast the wind carry them, and what effects they can have on polymeric materials. 

When using a macromer as a NAD, a high macromer content copolymer, called a comb polymer , is formed first. After the consumption of 1-3% of the total quantity of vinylic monomers, the resulting high macromer content copolymer is self-organised in the similar spherical proto-particles, which turn the reaction mass from transparent to opaque, with the carbocatenary polymeric part situated inside the spheres and the polyetheric chain situated outside the sphere, in the continuous liquid polyether phase. The next steps are identical to those of nonreactive NAD. The particles formed remain constant in number but increase in particle diameter size, the final diameter being around 10-20 times higher than the initial proto-particle diameter, of around 0.3-1 pm. 

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