Seed latex dispersion

Composite core-shell type microspheres were prepared by in situ heterogeneous polymerization on monodispersed seed latex particles suspended in an aqueous magnetite dispersion stabilized with sodium oleate (58). 

A similar seeding technique can be used to prepare monodispersed polymer latex dispersions by emulsion polymerisation (see page 17). 

Unlike the porous membrane, colloidal particles (such as PS or silica particle) are another type of template for the preparation of CPCs (Figure 11.10c). In previous work, core/shell PS/PANI composite particles were prepared by chemical oxidative seeded dispersion polymerization. A conventional coating protocol was employed as follows. The aniline monomer was dissolved in a strongly acidic solution in the presence of the PS seed latex (an alternative method involves using a miscible aniline hydrochloride monomer without external acid). Then polymerization was initiated by the addition of oxidant aqueous solution. The suspended PS particles were coated with PANI by in situ deposition of the formed conducting polymer or oligomer from the aqueous phase. 

Example 1 of Reference 34 describes a four-polymer IPN. A seed latex of butyl acrylate and 1,3-butylene dimethacrylate forms Cn. Onto this seed latex core, a shell of methyl methacrylate and glycidyl methacrylate are polymerized, forming P2. After coagulation, filtration, and washing, the resulting powder is dispersed in styrene and a stoichiometric amount of methacrylic acid. The dispersion is heated until the reaction between the methacrylic acid and the epoxy groups on the graded elastomeric particles is at least 50% complete. 

Ryan and Crochowski teach the use of acrylic latex IPNs dispersed in PVC copolymers to produce transparent, impact-resistant vinyls (see Table 8.1). A three-stage polymerization of the latex particles is required. A crosslinked rubbery latex such as poly(butyl acrylate) makes up the seed latex. A crosslinked vinyl aromatic, such as polystyrene, makes up network II. A linear poly(alkyl methacrylate), such as PMMA, forms polymer III. The finished latex is coagulated and blended with PVC to produce a tough, transparent plastic. Transparency is achieved by a close match of refractive indices. 

With suitable safety precautions, in a stirred, high pressure autoclave, with provisions of introducing a number of separate streams, are placed 3840 gm of distilled water, 160 gm of the seed latex described above, and 1200 gm of vinyl chloride. (The pH of this dispersion is 1.9.) With stirring, this dispersion is heated to 60°C and maintained at this temperature. The autoclave is then charged with ethylene until the pressure reaches 1200 psi (8.3 MPa). While this ethylene pressure is maintained, 200 gm of a 3% aqueous solution of sodium persulfate is charged to the autoclave. Then, simultaneously and continuously, three streams are added to the apparatus over a 13 hr period. These consist of (1) 4800 gm of vinyl chloride monomer, (2) 900 gm of a 3% aqueous solution of sodium persulfate, and (3) 1200 gm of a 10 7o aqueous solution of acrylic acid. 

Mono- or multimodal distributions of latex particles can be generated by controlling the amount, identity, and dispersion of soap and organic adjuvants (if microsuspension type) as well as by copolymerization or postaddition of seed latex. Small-particle PVC accounts for <5% of US productioa... 

Styrene and methyl methacrylate in the presence of the rubber seed latex particles. Finally, glycidyl methacrylate was grafted onto the composite latex particles. The emulsion polymerizations were stabilized by sodium dihexyl sulfosuccinate and initiated by potassium persulfate. The functionalized composite polymer particles, which served as an impact modifier, were blended with polyamide-6, and these particles were dispersed well in the matrix of polyamide-6. 

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. 

Seed polymerization using a polystyrene latex was used by Gaschler et al. (3) to prepare aqueous styrol-butadiene polymer dispersions. 

While vinyl acetate is normally polymerized in batch or continuous stirred tank reactors, continuous reactors offer the possibility of better heat transfer and more uniform quality. Tubular reactors have been used to produce polystyrene by a mass process (1, 2), and to produce emulsion polymers from styrene and styrene-butadiene (3 -6). The use of mixed emulsifiers to produce mono-disperse latexes has been applied to polyvinyl toluene (5). Dunn and Taylor have proposed that nucleation in seeded vinyl acetate emulsion is prevented by entrapment of oligomeric radicals by the seed particles (6j. Because of the solubility of vinyl acetate in water, Smith -Ewart kinetics (case 2) does not seem to apply, but the kinetic models developed by Ugelstad (7J and Friis (8 ) seem to be more appropriate. 

Polymer Colloid A dispersion of colloidal size polymer particles in a nonsolvent medium. Example submicroscopic latex spheres, prepared either by emulsion polymerization or by seeded emulsion polymerization, are used for a veriety of calibration purposes in colloid science. See reference 24. 

The method of preparing superparamagnetic particles developed by Charmot [109] uses hydrophobic non-porous polystyrene seed particles of narrow size distribution. A seeded polymerization is carried out to increase the particle size (1.35 pm) and a terpolymer is formed around the seed particles by a dispersion polymerization of styrene, DVB and 4-vinylpyridine in toluene. The toluene containing cobalt precursor swells the latex particles, which results in a homogeneous distribution of the metal precursor. A thermolysis reaction is conducted in the presence of 4-vinylpyridine, and the release of carbon monoxide indicates the decomposition of the metal salt into cobalt. The main problem of this method is the particle surface deformation during the evolution of carbon monoxide. The amount of crosslinker, however, cannot be reduced below a certain level without significantly modifying the properties of the particles. 

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