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Preformed latex dispersions

The reaction described in this example is carried out in miniemulsion.Miniemulsions are dispersions of critically stabilized oil droplets with a size between 50 and 500 nm prepared by shearing a system containing oil, water,a surfactant and a hydrophobe. In contrast to the classical emulsion polymerization (see 5ect. 2.2.4.2), here the polymerization starts and proceeds directly within the preformed micellar "nanoreactors" (= monomer droplets).This means that the droplets have to become the primary locus of the nucleation of the polymer reaction. With the concept of "nanoreactors" one can take advantage of a potential thermodynamic control for the design of nanoparticles. Polymerizations in such miniemulsions, when carefully prepared, result in latex particles which have about the same size as the initial droplets.The polymerization of miniemulsions extends the possibilities of the widely applied emulsion polymerization and provides advantages with respect to copolymerization reactions of monomers with different polarity, incorporation of hydrophobic materials, or with respect to the stability of the formed latexes. [Pg.187]

Polymeric Surfactants for Stabilisation of Preformed Latex Dispersions... [Pg.356]

The most common preformed rubber particles used as a toughening agent for epoxy polymers are the so-called structured, core-shell latex particles (Figure 4). These particles typically have a polybutadiene-based core and an acrylate-based shell. Such additives can be purchased as powders from Rohm and Haas or Elf-Atochem and can be purchased as epoxy concentrates from the Dow Chemical Company. The key parameter for these modifiers is the composition of the shell polymer, since the shell chemistry plays a crucial role in the overall blend morphology. It should be noted that it is possible to obtain commercial core-shell latex particles with reactive groups in the shell for improved dispersion of the rubber particles. [Pg.410]

An ab initio emulsion polymerisation involves the emulsification of one or more monomers in a continuous aqueous phase and stabilisation of the droplets by a surfactant. In a seeded emulsion polymerisation, one starts instead with a preformed seed latex. Usually, a water-soluble initiator is used to start the free-radical polymerisation. The locus of polymerisation is within the submicron polymer particles (either formed during the process or added at the start), which are swollen with monomer during the polymerisation process, and dispersed in the aqueous phase. The final product is a latex comprising a colloidal dispersion of polymer particles in water. Ab initio emulsion polymerisation differs from suspension, mini- and microemulsion polymerisations in that the particles form as a separate phase during the polymerisation process. The particle size is much smaller than those formed in a suspension polymerisation. [Pg.47]

Many manufacturing methods are available for the synthesis of latex particles exhibiting appropriate functionalities and three main approaches can be followed (a) polymerization in heterogeneous media (b) modification of preformed particles (see Arshady, 1999) (c) formulation of colloidal dispersions from preformed polymers. [Pg.262]

Dispersed polymers can be prepared in an aqueous environment in the presence of surfactants or preformed polymers can be dispersed in water with surfactants and high shear forces. These are called latex or emulsion polymers. [Pg.152]

Different approaches are used to prepare polymer particles with attaching to surface-functionalized groups. In majority of the cases, they consist of step-batch or -semibatch polymerizations in dispersed media, being among them pulsion polymerization (emulsifier-free or not) the most used polymerization process (i) emulsion homopolymerization of a monomer containing the desired functional group (functionalized monomer), (ii) emulsion copolymerization of styrene (usually) with the functionalized monomer, (iii) seeded copolymerization to produce composite functionalized latexes, and (iv) surface modification of preformed latexes. [Pg.264]


See other pages where Preformed latex dispersions is mentioned: [Pg.30]    [Pg.246]    [Pg.132]    [Pg.45]    [Pg.182]    [Pg.155]    [Pg.435]    [Pg.463]    [Pg.258]    [Pg.346]    [Pg.75]    [Pg.372]    [Pg.43]    [Pg.527]    [Pg.265]    [Pg.155]    [Pg.319]    [Pg.333]    [Pg.22]    [Pg.66]    [Pg.664]   
See also in sourсe #XX -- [ Pg.356 , Pg.357 , Pg.358 , Pg.359 ]




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