Synthesis of Polymer Dispersions

2-2 Laboratory equipment for emulsion polymerization at high pressures (photograph courtesy BASF Corporation). 

A simple recipe, which could be used to demonstrate the influence of ingredients and process on polymer and colloidal properties, is shown in Tab. 2-1. Subsequent sections of this chapter give greater detail on materials used to produce emulsion polymers. 

This recipe could be utilized for investigating both batch and semi-batch emulsion polymerization at a range of temperatures. With just these two monomers and one functional monomer, a very wide range of polymers with significant differences in polymer and latex properties can be produced (soft/hard, low/high molecular weight, tacky/non-tacky, stable/unstable, etc.) 

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Taylor, M. (2002) Synthesis of polymer dispersions. In D. Urban and K. Takamura (eds). Polymer Dispersions and Their Industrial Applications. WUey-VCH, Weinheim. 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

The control of the synthesis of polymers is crucial to obtain the final bulk properties of the polymers needed for the end application. The use of enzymes in polymer synthesis has been demonstrated to allow control of polymer properties such as average molecular weight and dispersity, avoid the use of toxic intermediates, enable the selective reaction of functional groups and allow the use of unstable intermediates. 

Although the word processing is normally reserved for the method of manufacture of any finished article it is important to recognise that the word can also describe the preparation or synthesis of the material. Thus in the polymer field it can range from improved methods of synthesis of polymers with tailor made properties (see Section 5.5) to improved methods of dispersion or improved methods of extrusion. Typical technological uses are shown in Tab. 5.25. 

An alcohol reduction method has been applied to the synthesis of polymer-stabilized bimetallic nanoparticles. They have been prepared by simultaneous reduction of the two corresponding metal ions with refluxing alcohol. For example, colloidal dispersions of Pd/Pt bimetallic nanoparticles can be prepared by refluxing the alcohol-water (1 1 v/v) mixed solution of palladium(II) chloride and hexachloro-platinic(IV) acid in the presence of poly(/V-vinyl-2-pyrrolidone) (PVP) at about 90-95°C for 1 h (Scheme 9.1.5) (25). The resulting brownish colloidal dispersions are stable and neither precipitate nor flocculate over a period of several years. Pd/ Pt bimetallic nanoparticles thus obtained have a so-called core/shell structure, which is proved by an EXAFS technique (described in Section 9.1.3.3). 

It is reasonable that, in the synthesis of polymer nanocomposites, the y-ray irradiation method is convenient for growing nanofibers and nanowires of metal chalcogenides due to the shape-control of the macromolecules formed in situ. Figure 7.38 shows some of the resulting nanofiber-dispersed polymer composites,... 

The environmentally benign, nontoxic and nonflammable fluids water and carbon dioxide (CO2) are the two most abundant and inexpensive solvents on earth. Vater-in-CO2 (W/C) or C02-in-water (C/W) dispersions in the form of microemulsions and emulsions offer new possibilities in waste minimization for the replacement of organic solvents in fields including chemical processing, pharmaceuticals, and microlectronics for solubilization and separations (e.g., proteins, ions, heavy metals), particle formation, enzymatic catalysis, organometallic catalysis, and synthesis of polymer colloids and inorganic nanoparticles (2,13,11). 

Note that MW of the samples synthesized using closo complexes, are noticeably lower as compared to the polymers obtained in the presence of either the exo-nido complexes or conventional radical initiators (such as AIBN and peroxides) where the molecular weights of polyacrylates range from several hundred thousands to several millions. Since mthenacarboranes with the closo stmcture are more promising for the synthesis of narrow-dispersed polymers, we studied the kinetics of MMA polymerization in the presence of the above mentioned catalysts and analyzed the molecular-weight characteristics of the polymers in more detail, using complex 4 as an example. 

The use of functional monomers permits ready control of the content and sometimes the distribution of units along the polymer chain this procedure gives more latitude concerning the physical properties of the final product. On the other hand, chemical modification of an existing polymer, when possible, enables the choice of molecular weight and the dispersity of the polymer. It also allows the synthesis of polymers inaccessible by direct route. 

Disperse oxides unmodified or modified by organics (OC) or OSC are used as fillers, adsorbents, or additives [1-11]. OSCs are used as promoters of adhesion, inhibitors of corrosion, for the stabilization of monodisperse oxides and the formation of the nanoscaled particles. Oxide modification by alcohols or other OC is of interest for synthesis of polymer fillers, as such modification leads to plasticization and reinforcement of the filled coating, but in this case a question arises about hydrolyz-ability of the =M—O—C bonds between oxide surface and alkoxy groups, as those are less stable than =M—O— M= formed, for example, upon the silica modification by silanes or siloxanes. The high dispersity, high specific surface area, and high adsorption ability of fumed oxides have an influence on their efficiency as fillers of polymer systems. 

Synthesis of polymer microspheres in the presence of magnetic nanoparticles, such as suspension polymerization or its modified versions, dispersion polymerization, surface-initiated radical polymerization, acid-catalyzed condensation polymerization, emulsion polymerization, mini-/microemulsion polymerization, in situ oxidative polymerization, inverse emulsion cross-linking, emulsion/double emulsion-solvent evaporation, and supercritical fluid extraction of o/w miniemulsion... 

Polypyrrole and many of its derivatives can be synthesized via simple chemical or electrochemical methods [120]. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but less developed. Different synthesis routes produce polypyrrole with different forms chemical oxidations generally produce powders, while electrochemical synthesis leads to films deposited on the working electrode and enzymatic polymerization gives aqueous dispersions [Liu. Y. C, 2002, Tadros. T. H, 2005 and Wallace. G. G, 2003]. As mentioned above the electrochemical polymerization method is utilized extensively for production of electro active/conductive films. The film properties can be easily controlled by simply varying the electrolysis conditions such as electrode potential, current density, solvent, and electrolyte. It also enables control of thickness of the polymers. Electrochemical synthesis of polymers is a complex process and various factors such as the nature and concentration of monomer/electrolyte, cell conditions, the solvent, electrode, applied potential and temperature, pH affects the yield and the quality of the film... 

An alcohol reduction method in which alcohol like ethanol can work both as a reductant and a solvent has been applied to the synthesis of polymer-capped bimetallic nanoclusters. They have been prepared by the simultaneous reduction of the two corresponding metal ions with refluxing alcohol. For example, colloidal dispersions of Pd/Pt bimetallic nanoclusters can be prepared by refluxing... 

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