142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

168 K. Ito, S. Kawaguchi
the polymerization include monomer, water, surfactants, and initiators. Upon
mixing, the surfactant molecules cluster into micelles and their hydrophobic
cores are swollen with monomer. Their diameters are typically of the order of
50–150 Å, and their number density is of the order of 10 17 –10 18 dm –3 . The bulk
of the monomer, however, exists in the form of large-size droplets with surfactant
molecules adsorbed on their surfaces; their diameters are typically in the
range of 1–10 µm, and their number density of the order of 10 9 –10 11 dm –3 .
Therefore, the polymerization is believed to take place in the micellar phase, the
aqueous phase, the monomer droplet phase, and the particle phase. Three major
mechanisms have been proposed for particle formation in emulsion polymerization
– micellar, homogeneous, and droplet nucleation – depending on the surfactant
concentration, the monomer solubility in the aqueous phase, and the extent
of subdivision of the monomer droplets. This has been a central subject in
the emulsion polymerization for a long time and is still a controversial issue.
Instead of conventional surfactant molecules, amphiphilic water soluble macromonomers,
especially PEO macromonomers, have been used extensively as a
reactive emulsifier and as steric stabilizer polymer, as summarized in Table 5.
Generally speaking, however, the mechanism for the particle nucleation in the
emulsion polymerization systems using macromonomers has been poorly established
when compared to the dispersion copolymerizations with macromonomers
as mentioned earlier.
The first work on the emulsion copolymerization with a macromonomer has
been reported by Ito et al. [132] for styrene using PEO macromonomer 49. Subsequently,
several research groups have reported the synthesis and some properties
of latex particles containing PEO chains from 26, 27, 36, 50–52, attached
to their particles surface [132–140]. Ottewill and Satgurunathan [134] and Westby
[135] reported the preparation of such particles in a multistage emulsion po-
Table 5. Examples of emulsion copolymerization with macromonomers
Macromonomer Monomer Ref.
PEO, 49 Styrene 132
PEO, 36 Styrene 133
PEO 27b Styrene 134
PEO 27b Butyl acrylate 135
PEO 50 Styrene 136
PEO 26 (m=7) Styrene 137
PEO 26(m=1, 11), 27a(m=10), 27b, 51, 52 Styrene 138
PEO 27a (m=11) Styrene 139
PEO 26(m=1, 4, 7) Styrene 140
POXZ 34 Styrene 143
POXZ 53 Styrene 144
POXZ 54 Styrene 145
POXZ 55 Vinyl acetate 146
PMA 48 Styrene 127