Heterophase polymerizations

Polymerizations conducted in nonaqueous media in which the polymer is insoluble also display the characteristics of emulsion polymerization. When either vinyl acetate or methyl methacrylate is polymerized in a poor solvent for the polymer, for example, the rate accelerates as the polymerization progresses. This acceleration, which has been called the gel effect,probably is associated with the precipitation of minute droplets of polymer highly swollen with monomer. These droplets may provide polymerization loci in which a single chain radical may be isolated from all others. A similar heterophase polymerization is observed even in the polymerization of the pure monomer in those cases in which the polymer is insoluble in its own monomer. Vinyl chloride, vinylidene chloride, acrylonitrile, and methacryloni-trile polymerize with precipitation of the polymer in a finely divided dispersion as rapidly as it is formed. The reaction rate increases as these polymer particles are generated. In the case of vinyl chloride ... 

Heterophase polymerization in general is a current trend in polymer science as it allows solvent-free polymer synthesis polymer powders are obtained when the dispersion agent is removed. DeSimone improved this procedure significantly by performing the heterophase polymerization in supercritical C02, which simplifies the synthesis of powders with excellent handling of the polymerization and evaporation process.7 9... 

Equation (8) has been used to describe the progress of the homogeneous polymerization up to conversions of approximately 60%. Experimental and calculated conversion-time curves were in good agreement, even for the case of changing experimental conditions during the polymerization [51]. For the heterophase polymerization experimental and modeled conversion-time curves coincide well if a kinetic model based on first order initiator decomposition was applied and consideration of gel effect for conversions greater than 35% was included [13]. 

Guan, Z. DeSimone, J. M. Fluorocarbon-Based Heterophase Polymeric Materials. 

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. 

Schoonbrood, H.A.S., Unzue, MJ., Beck, O. and Asua, J.M. (1997) Reactive surfactants in heterophase polymerization. 7. Emulsion copolymerization mechanism involving three anionic polymerizable surfactants (surfmers) with styrene-butyl acrylate acrylic acid. Macromolecules, 30, 6024-33. 

Sindt, O., Gauthier, C., Hamaide, T. and Guyot, AJ. (2000) Reactive surfactants in heterophase polymerization. XVI. Emulsion copolymerization of styrene-butyl acrylate-acrylic acid in the presence of simple maleate reactive surfactants. /. Appl. Polym. Sci, 77,2768-76. 

Keywords. Polymer latex, Miniemulsion, Heterophase polymerization, Polymer nanoparticles, Composite particles... 

In the case of inverse systems, hydrophilic monomers such as hydroxyethyl acrylate, acrylamide, and acrylic acid were miniemulsified in non-polar media, e.g., cyclohexane or hexadecane [45,46]. Rather small and narrow distributed latexes in a size range between 50 nmsynthesized with nonionic amphiphilic block copolymers. Depending on the system, the surfactant loads can be as low as 1.5 wt% per monomer, which is very low for an inverse heterophase polymerization reaction and clearly underlines the advantages of the miniemulsion technique. 

As compared to classical inverse heterophase polymerization techniques such as polymerization in inverse micro emulsions [47] or dispersion polymerization [75,76], polymerization of inverse miniemulsions is favored by the very efficient use of surfactant and the copying process from the droplets to the par-... 

Microgels can be prepared by heterophase polymerization (free radical or controlled radical) of monomers in the presence of a crosslinking agent in aqueous phase. Heterophase polymerization techniques suitable for microgel synthesis are precipitation polymerization and inverse mini- and microemulsion. 

---