Colloidal polymer dispersions

Podorozhko EA, D yakonovaEA, Kolosova OY, KlabukovLF, Lozinsky VI (2012) A study of cryostructuring of polymer systems. 34. Poly(vinyl alcohol) composite cryogels filled with microparticles of polymer dispersion. Colloid J 74 708... 

In mass polymerization bulk monomer is converted to polymers. In solution polymerization the reaction is completed in the presence of a solvent. In suspension, dispersed mass, pearl or granular polymerization the monomer, containing dissolved initiator, is polymerized while dispersed in the form of fine droplets in a second non-reactive liquid (usually water). In emulsion polymerization an aqueous emulsion of the monomer in the presence of a water-soluble initiator Is converted to a polymer latex (colloidal dispersion of polymer in water). 

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. 

The interfacial properties of chain-like molecules in many polymeric and colloidal systems are dependent on the conformation of the chains adsorbed at the interface (.1). Chains adsorbed at the solid-liquid interface may be produced by anchoring diblock copolymers to particles in a polymer dispersion. Such dispersions are conveniently prepared by polymerizing in the presence of a preformed AB diblock copolymer a monomer dissolved in a diluent which is a precipitant for the polymer. The A block which is... 

I I heology is an integral part of life, from decorative paint and movement of volcanic lava to the flow of blood in our veins. This book describes, without the use of complex mathematics, how atoms and molecules interact to control the handling properties of materials ranging from simple ionic crystals through polymers to colloidal dispersions. 

These colloidals are dispersed in aqueous media, and exhibit twofold progenies polymers and colloidals. 

Tachibana T, Nakamura A. A method for preparing an aqueous colloidal dispersion of organic materials by using water-soluble polymers dispersion of beta-carotene by polyvinylpyrrolidone. Kolloid-Z Polym 1965 203 130-133. 

Napper, D. H., Polymeric Stabilization of Colloidal Dispersions, Academic Press, London, 1983. (Graduate-level monograph. An advanced and in-depth treatment of the role of polymers in colloid stability.)... 

A second kind of polymer, a colloidal aqueous dispersion, was reported by Renfrew (1950) who used bis- (/ -carboxypropionyl) peroxide as the polymerization initiator, and later described in more detail by Lontz and Happoldt. The specific surface of dispersion polymer is on the order of 12 m2/g, and the equivalent surface average diameter for dense spheres is about 0.2 fi. This is a good check with the observed size seen in the electron micrograph of Fig. lb and indicates that the primary dispersion particles have little, if any, porous structure. 

The colloidal stable polymer dispersions, the monodisperse polymer particles, and high conversions (85-100%) can be obtained with most of the other macromonomers (MAL,VB, and MA) of PEO (MW>PEO=2000)) [76]. Also, when macromonomers are used (3.1 wt% based on styrene), there is practically no coagulum produced. This is not the case in the presence of polymerizable PEO surfactants (surfmer I R1=CH3(CH2)11-, R2=H, n=34 and surfmer II R =CH3 (CH2)n-, R2=H, n=42) despite the higher amounts of stabilizer used (up to 60 wt% of coagulum). Furthermore, the particles are more monodisperse with PEO macromonomer (Dw/Dn=1.025 for PEO-MA and 1.13 for PVPo) compared to those with surfmer. Comparatively poorer results were obtained with conventional surfactants such as ethoxylated nonylphenol, even when used in large amounts. 

The colloidal stability of polymer dispersion prepared by the emulsion copolymerization of R-(EO)n-MA was observed to increase with increasing EO number in the macromonomer [42, 96]. Thus C12-(EO)9-MA did not produce stable polymer latexes, i.e., the coagulum was observed during polymerization. This monomer, however, was efficient in the emulsion copolymerization with BzMA (see below). The C12-(EO)20-MA, however, appears to have the most suitable hydrophilic-hydrophobic balance to make stable emulsions. The relative reactivity of macromonomer slightly decreases with increasing EO number in macromonomer. The most hydrophilic macromonomer with co-methyl terminal, Cr(EO)39-MA, could not disperse the monomer so that the styrene droplets coexisted during polymerization. The maximum rate of polymerization was observed at low conversions and decreased with increasing conversion. The decrease in the rate may be attributed to the decrease of monomer content in the particles (Table 2). In the Cr(EO)39-MA/St system the macromonomer is soluble in water and styrene is located in the monomer droplets. Under such conditions the polymerization in St monomer droplets may contribute to the increase in r2 values. 

Polymer colloids involve dispersions containing polymer particles having sizes greater than about 1 nm. If dispersed in aqueous solution, such a polymer dispersion is called a latex. These are usually synthetic polymer particles formed by free radical polymerization [784], Many kinds of polymerization systems exist, involving almost all of the possible kinds of colloidal dispersion, including emulsion polymerization, hence the more general term heterophase polymerization is sometimes used. Several reviews are available [785-789]. Emulsion polymerization provides a convenient means of controlling the polymerization of monomers and is used to make, for example, synthetic rubber which is mostly a co-polymer of butadiene and styrene. 

Products comprising hydrophilic polymers dissolved in water are well-known and used widely as adhesives but are of little general significance for bonding plastics. The present chapter is concerned only with products based on polymer dispersions, which consist of small discrete particles of diameter about one micron (1 pm, or 10-3 mm) suspended in a continuous water phase. In most instances a protective colloid is present at the interface between the particles of polymer and the water and this helps to stabilize the dispersion and prevent premature coalescence of particles. Dispersions such as these are known as oil-in-water types. With them, the molar mass of the polymer species comprising the dispersed particles does not affect the viscosity and so polymers of high molecular weight can be applied in this way. 

Interactions between soluble polymer and colloidal particles control the behavior of a large number of chemical products and processes and, hence, their technological viability. These dispersions have also attracted considerable scientific interest because of their complex thermodynamic and dynamical behavior—stimulated by the synthesis of novel polymers, improved optical and scattering techniques for characterization, and a predictive capability emerging from sophisticated statistical mechanical theories. Thus, the area is active both industrially and academically as evidenced by the patent literature and the frequency of technical conferences. 

Polymers in the form of latex (colloidal dispersions) acquire a novel quality not observed in bulk or solution and which is due to the strongly developed interface with the aqueous phase, The properties of this interface va ry specifically with the nature of the polymer, the latter varying in a wide range for different latexes and other polymer dispersions. 

Bodmeier, R. Paeratakul, O. Mechanical properties of dry and wet cellulosic and acrylic films prepared from aqueous colloidal polymer dispersions used in the coating of solid dosage forms. Pharm. Res. 1994, 11 (6), 882-888. 

Bodmeier, R. Paeratakul, O. The distribution of plasticizers between aqueous and polymer phases in aqueous colloidal polymer dispersions. Int. J. Pharm. 1994, 103, 47-54. 

Wong, D. Practical considerations for stabilization of aqueous colloidal polymer dispersions. Pharm. Tech. 1997, 21, 38-50. 

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