Surfactant-water system polymeric

The first part of the book discusses formation and characterization of the microemulsions aspect of polymer association structures in water-in-oil, middle-phase, and oil-in-water systems. Polymerization in microemulsions is covered by a review chapter and a chapter on preparation of polymers. The second part of the book discusses the liquid crystalline phase of polymer association structures. Discussed are meso-phase formation of a polypeptide, cellulose, and its derivatives in various solvents, emphasizing theory, novel systems, characterization, and properties. Applications such as fibers and polymer formation are described. The third part of the book treats polymer association structures other than microemulsions and liquid crystals such as polymer-polymer and polymer-surfactant, microemulsion, or rigid sphere interactions. 

Fig. 5.15. Phase diagram of the polymeric surfactant-water system. Black region represents bicontinuous cubic phase, Vj.

Various initiation strategies and surfactant/cosurfactant systems have been used. Early work involved in situ alkoxyamine formation with either oil soluble (BPO) or water soluble initiators (persulfate) and traditional surfactant and hydrophobic cosurfactants. Later work established that preformed polymer could perform the role of the cosurfactant and surfactant-free systems with persulfate initiation were also developed, l90 222,2i3 Oil soluble (PS capped with TEMPO,221 111,224 PBA capped with 89) and water soluble alkoxyamines (110, sodium salt""4) have also been used as initiators. Addition of ascorbic acid, which reduces the nitroxide which exits the particles to the corresponding hydroxylamine, gave enhanced rates and improved conversions in miniemulsion polymerization with TEMPO.225 Ascorbic acid is localized in the aqueous phase by solubility. 

Large volumes of soap are used in industrial applications as gelling agents lor kerosene, paint driers, and as surfactants in emulsion polymerization. See also Soaps. Concern over water eutrophication resulted in a ban of phosphorus in laundry detergents. Phosphates have been effectively replaced by combinations of zeolite, citrate, and polymers, coupled with rebalanced synthetic active systems. Soap itself is generally present only as a minor component of surfactants. 

The emulsion polymerization methodology is one of the most important commercial processes. The simplest system for an emulsion (co)polymerization consists of water-insoluble monomers, surfactants in a concentration above the CMC, and a water-soluble initiator, when all these species are placed in water. Initially, the system is emulsified. This results in the formation of thermodynamically stable micelles or microemulsions built up from monomer (nano)droplets stabilized by surfactants. The system is then agitated, e.g., by heating it. This leads to thermal decomposition of the initiator and free-radical polymerization starts [85]. Here, we will consider a somewhat unusual scenario, when a surfactant behaves as a polymerizing comonomer [25,86]. 

Miniemulsion polymerization involves the use of an effective surfactant/ costabilizer system to produce very small (0.01-0.5 pm) monomer droplets. The droplet surface area in these systems is very large, and most of the surfactant is adsorbed at the droplet surface. Particle nucleation is primarily via radical (primary or oligomeric) entry into monomer droplets, since little surfactant is present in the form of micelles, or as free surfactant available to stabihze particles formed in the continuous phase. Both oil- and water-soluble initiators may be used the important feature is that the reaction proceeds by polymerization of the monomer in these small droplets, so there is no true Interval II. The mechanisms of macro- and miniemulsion polymerization are shown schematically in Fig. 1. 

Emulsion polymerization is an important commercial process because, in contrast to the same free-radical polymerization performed in the bulk, molecular weight and reaction rate can be increased simultaneously (1-3). Furthermore, the lower viscosity of an emulsion system compared with that of the corresponding bulk process provides better control over heat transfer. Commercial emulsion processes usually use a surfactant/water/monomer system... 

For the model system polymerizations, solutions containing the surfactants, LMA, initiator, and other additives as necessary were prepared in 4-oz narrow-mouth bottles, placed in a Branson B-52 ultrasonic bath for more than 10 min with nitrogen flow into the top of the bottle, capped with Polyseal tops, and tumbled in a water bath overnight at 60 °C. The ultrasonic bath was used both to aid in degassing the sample and to ensure complete equilibrium in the surfactant solutions. 

As explained before, when surfactant, water, and monomer(s) are mixed, the colloidal system obtained consists of monomer-swollen micelles (if the surfactant concentration exceeds its CMC) and monomer droplets dispersed in an aqueous phase that contains dissolved molecules of surfactant and a small amount of the sparingly water-soluble monomer(s). When free radicals are generated in the aqueous phase by action of an initiator system, then the emulsion polymerization takes place. Its evolution is such that the colloidal entities initially present tend to disappear and new colloidal entities (polymer latex particles) are bom by a process called nucleation. For convenience, we first focus on the particle nucleation mechanisms, a very important aspect of emulsion polymerization. 

Fluoropolymers are typically synthesized in aqueous polymerization systems (both emulsion and suspension), non-aqueous systems (Freon-113), or Freon-113/aqueous hybrid systems [8]. Such processes require the use of large quantities of water and CFCs (for non-aqueous polymerizations) or fluorinated surfactants (for emulsion polymerization). Aqueous suspension and dispersion poly-... 

This exclusion of polymers from the interior of the vesicles results in an osmotic compression of the water layers and a decrease in the water layer thickness and lamellar phase volume. This effect allows the control of bulk properties such as viscosity and also provides a probe of water layer dimensions in lamellar dispersions. The lamellar surfactant system used in this study is the sodium dodecyl sulfate (SDS)/dodecanol (Ci20H)/water system that has been used to prepare submicron diameter emulsions (miniemulsions) from monomers for emulsion polymerization (5) and for the preparation of artificial latexes by direct emulsification of polymer solutions such as ethyl cellulose (4). This surfactant system forms lamellar dispersions (vesicles) in water at very low surfactant concentrations (< 13 mM). 

In addition to electrostatic colloid stabilization generated by anionic surfactants, liquid dispersions are also made from nonionic surfactants. Stabilization of the emulsion is achieved by electrosteric stabilization or by pure steric stabilization (2,13). Polyoxyethylene dodecyl ethers, polyoxyethylene nonyl phenyl ethers, and polyoxyethylene nonyl phenol ethers are a few surfactants typically used in emulsion polymerization with nonionic surfactants (14-16). Non-ionic emulsion polymerizations are characterized by lower critical micelle concentration than their ionic counterparts. Thus, the emulsion particle sizes are generally much larger than in the ionic polymerizations. The mechanism of radical entry and exit in polymeric surfactant stabilizer systems are different than in anionic systems. With water-soluble initiators, the kinetics depends on initiator concentration. 

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