Soapless emulsion polymerization

When the emulsion polymerization is conducted in the absence of an emulsifier, this process is termed emulsifier free or soapless emulsion polymerization [68-73]. In this case, the particle formation occurs by the precipitation of growing macroradicals within the continuous... 

With some limitations. Single-stage soapless emulsion polymerization can be used for the direct copolymerization of a relatively apolar monomer with a polar... 

DSEP direct soapless emulsion polymerization, SSEC seeded soapless emulsion copolymerization, DDC direct dispersion copolymerization, TDSC two-stage dispersion copolymerization, ATES Allyl trietoxysilane, VTES vinyl trietoxysilane, DMAEM dimethylaminoethyl-methacrylate, CMS chloromethylstyrene, GA glutaraldehyde, AAc Acrylic acid Aam Acrylamide HEMA 2-hydroxyethylmethacrylate. 

The soapless seeded emulsion copolymerization method was used for producing uniform microspheres prepared by the copolymerization of styrene with polar, functional monomers [115-117]. In this series, polysty-rene-polymethacrylic acid (PS/PMAAc), poly sty rene-polymethylmethacrylate-polymethacrylic acid (PS/ PMMA/PMAAc), polystyrene-polyhydroxyethylmeth-acrylate (PS/PHEMA), and polystyrene-polyacrylic acid (PS/PAAc) uniform copolymer microspheres were synthesized by applying a multistage soapless emulsion polymerization process. The composition and the average size of the uniform copolymer latices prepared by multistage soapless emulsion copolymerization are given in Table 11. 

Preparation of uniform seed particles Soapless emulsion polymerization is usually preferred for the preparation of uniform seed particles since this technique provides emulsifier-free, larger, and highly uniform micropheres relative to those that can be obtained by the conventional emulsion recipes including emulsifiers and various additives. The size of uniform seed particles with the soapless emulsion procedure is in the range of 0.6-1.2 tm depending on the polymerization conditions [75,108]. 

Fig. 14 (a) Mechanisms proposed in [112] for particle nucleation and growth in the case of MMA soapless emulsion polymerization in the presence of Fe304 coated with a bilayer of lauric acid, (b) TEM image of an example of composite magnetic particles obtained. Adapted from [112] with permission of Wiley Periodicals... 

Liu Y, Liu P, Su Z (2008) Morphological characterization of attapulgite/poly(methyl methacrylate) particles prepared by soapless emulsion polymerization. Polym Int 57 306-310... 

M. Hasegawa, K. Arai, S. Saito, Effect of surfactant adsorbed on encapsulation of fine inorganic powder with soapless emulsion polymerization, J. Polym. Sci., Part A Polym. Chem., 1987, 25,3231-3239. 

The ionic nature of the radicals generated, by whatever technique, can contribute to the stabilization of latex particles. Soapless emulsion polymerizations can be carried out using potassium persulfate as initiator (126). It is often important to control pH with buffers during soapless emulsion polymerization. 

A theoretical treatment of soapless emulsion polymerization of methyl methacrylate in water has shown that the number of particles is determined during the initial stages, and has clarified the relationships between this method, normal emulsion polymerization, and bulk polymerization. Differences between the heterogeneous polymerization of acrylonitrile and vinyl chloride have been discussed, following the development of an elaborate model for the former case in which propagation proceeds in the liquid and, eventually, also in the solid phase. ... 

According to the other kinetic model proposed for the soapless emulsion process, the growing macroradicals may also form micelle structures at earlier polymerization times since they have both a hydrophilic end coming from the initiator and a hydrophobic chain [74]. 

The uniform polymeric microspheres in submicron-or micron-size range can also be prepared as seed particles by the soapless emulsion or dispersion polymerization of a hydrophobic monomer like styrene. The uniform seed particles are swollen with the organic phase including functional comonomer, monomer, and oil-soluble initiator at a low temperature in an aqueous... 

PS/PHEM A particles in micron-size range were also obtained by applying the single-stage soapless emulsion copolymerization method [124]. But, this method provided copolymer particles with an anomalous shape with an uneven surface. PS or PHEMA particles prepared by emulsifier-free emulsion polymerization were also used as seed particles with the respective comonomer to achieve uniform PS/PHEMA or PHEMA/PS composite particles. PS/PHEMA and PHEMA/PS particles in the form of excellent spheres were successfully produced 1 iLitm in size in the same study. 

Soapless seeded emulsion copolymerization has been proposed as an alternative method for the preparation of uniform copolymer microspheres in the submicron-size range [115-117]. In this process, a small part of the total monomer-comonomer mixture is added into the water phase to start the copolymerization with a lower monomer phase-water ratio relative to the conventional direct process to prevent the coagulation and monodispersity defects. The functional comonomer concentration in the monomer-comonomer mixture is also kept below 10% (by mole). The water phase including the initiator is kept at the polymerization temperature during and after the addition of initial monomer mixture. The nucleation takes place by the precipitation of copolymer macromolecules, and initially formed copolymer nuclei collide and form larger particles. After particle formation with the initial lower organic phase-water ratio, an oligomer initiated in the continuous phase is... 

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