Water-soluble free-radical addition

WATER-SOLUBLE FREE RADICAL ADDITION POLYMERIZATIONS... 

Essentially, TFE in gaseous state is polymerized via a free radical addition mechanism in aqueous medium with water-soluble free radical initiators, such as peroxy-disulfates, organic peroxides, or reduction-activation systems.15 The additives have to be selected very carefully since they may interfere with the polymerization. They may either inhibit the process or cause chain transfer that leads to inferior products. When producing aqueous dispersions, highly halogenated emulsifiers, such as fully fluorinated acids,16 are used. If the process requires normal emulsifiers, these have to be injected only after the polymerization has started.17 TFE polymerizes readily at moderate temperatures (40 to 80°C) (104 to 176°F) and moderate pressures (0.7 to 2.8 MPa) (102 to 406 psi). The reaction is extremely exothermic (the heat of polymerization is 41 kcal/mol). 

The general reactivity of higher a-olefins is similar to that observed for (he lower olefins. However, heavier a-olefins have low solubility in polar solvents such as water consequently, in reaction systems requiring the addition of polar reagents, apparentreactivity and degree of conversion may be adversely affected. Reactions of a-olefins typically involve the carbon-carbon double bond and can be grouped into 1 wo classes (1) electrophilic or free-radical additions and (2) substitution reactions. 

Recently, we have developed a relatively green process for covalently functionalizing nanotubes. Versatile functional groups were covalently anchored onto MWCNTs by one-step free radical addition of water-soluble azo initiators in water, and their coverage densities were easily controlled by adjusting feed ratio of initiators to... 

Yang YK, Qiu SQ, Xie XL et al (2010) A facile, green, and tunable method to functionalize carbon nanotubes with water-soluble azo initiators by one-step free radical addition. Appl Surf Sci 256 3286-3292... 

A monomer, typically 2-bydroxyetbyl methacrylate, HEMA (Fig. 7.1), which is water soluble and capable of undergoing rapid free radical addition polymerization to create part of the matrix of the set cement-polymeric matrix. 

Emulsion pol)m erization is a complex process in which the radical addition polymerization proceeds in a heterogeneous system. This process involves emulsification of the relatively hydrophobic monomer in water by an oil-in-water emulsifier, followed by the initiation reaction with either a water-soluble or an oil-soluble free radical initiator. At the end of the pol)nnerization, a milky fluid called "latex", "synthetic latex" or "pol)rmer dispersion" is obtained. Latex is defined as "colloidal dispersion of polymer particles in an aqueous medium". The pol)nner may be organic or inorganic. In general, latexes contain 40-60 % pol)nner solids and comprise a large population of polymer particles dispersed in the continuous aqueous phase (about lO particles per mL of latex). The particles are within the size range 10 nm to 1000 run in a diameter and are generally spherical. A typical of particle is composed of 1-10000 macromolecules, and each macromolecule contains about lOO-lO " monomer units [10-16]. 

In 2009, an estimated four billion metric tons of natural, semisynthetic, and synthetic water-soluble polymers were consumed globally for use in the production of food, clean water, energy, for personal care, pharmaceutical, and industrial applications [1], Synthetic water-soluble polymers synthesized by free radical addition polymerization methods account for half of this volume. They include polyacrylamides, polyacrylates, polydiaUyldimethylammonium chloride (polyDAD-MAC), polyvinyl alcohol, and polyvinylpyrrolidones. Depending on the target applications, these polymers can have different molecular weight, charge, and architecture. 

Heesche-Wagner, K. Mitchell, T.N. (1994) Approaches to water-soluble phosphines. 2. Free-radical addition-reactions of phenylphosphines, J. Organomet. Chem., 4, 99-106. 

Commercially, suspension polymerization has been hmited to the free-radical addition of water-insoluble liquid monomers. With a volatile monomer such as vinyl chloride, moderate pressures are required to maintain it in the hquid state. It is possible, however, to perform inverse suspension polymerizations with a hydrophilic monomer or an aqueous solution of a water-soluble monomer suspended in a hydrophobic continuous phase. 

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

The additional protection given to nylon by antioxidants has already been mentioned. Since the need is to protect against oxidation by free radicals, antioxidants are essentially of two types peroxide decomposers and radical scavengers. Reviews of these products are available [409,410,413] these should be consulted for details of the mechanisms involved. Peroxide decomposer types include compounds of manganese (II) or copper(I) and copper(II) complexes, such as azomethine bridge derivatives of the type represented by 10.160, of which numerous water-soluble or water-insoluble variants are possible [409]. These products have a catalytic action and are therefore used in very small amounts. 

Coatings emulsions are generally formed by addition polymerization of common, highly available monomers, using free radical initiators to create polymers having molecular weights from a few thousand up to millions. The polymerization is most often stabilized by non-ionic and/or anionic surfactants, which emulsify the insoluble monomer droplets, and then stabilize the resulting particles, usually in the shape of a sphere. In addition to surfactants, emulsions are sometimes stabilized with water-soluble poly-... 

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