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

170 K. Ito, S. Kawaguchi
size was found to increase with increasing the neutralization of the polyelectrolyte
macromonomers.
The rate of polymerization, R p , in the emulsion polymerization is generally
given by the equation
(30)
where n
is the average number of radicals per particle, N the number of latex
particles per unit volume, and [M] p, the equilibrium concentration of the monomer
swelling the latex particle. According to the Smith-Ewart theory [147], in
which the main locus for particle nucleation is assumed to take place in the surfactant
micelles, the number of particles is given as
(31)
where r' is the rate of radical generation, µ is the rate of particle volume growth,
a s is the area occupied by a surfactant molecule, and C s is the total amount of
surfactant in the micelles. Gardon [148, 149] thoroughly reviewed and confirmed
the assumptions of Smith-Ewart theory and derived the more convenient
equation for numerical calculation:
(32)
where r'=2N A k d f[I], C s =N A ([C s ]–[cmc]), and K=[(3/4p)(k p /N A )(d m /d p )f m ]/(1–
f m ) with the monomer and polymer density, d m , d p , and the volume fraction of
monomers swelling the particles at equilibrium, f m . These equations have been
well established to hold for the conventional emulsion polymerization of hydrophobic,
water insoluble monomers such as styrene. Therefore, when one assumes
that micellar entry dominates the particle nucleation in the emulsion copolymerization
of styrene with a macromonomer, N may be written by the following
power law relationship:
(33)
Sauer and coworkers [138] obtained Nµ [I] 0.82 [Macromonomer] –0.2~+0.82 in
the styrene emulsion copolymerization with various types of PEO macromonomers,
26, 27, 51, and 52. On the other hand, it has been found that using a PEO
macromonomer, 26 (m=1, 4, 7), with a relatively short PEO chain (n=16), Nµ
[Macromonomer] 0.6 while using a macromonomer with a moderately long PEO
chain (n=45), Nµ [Macromonomer] 1.8 [140]. A mechanistic model for the emulsion
copolymerization using amphiphilic macromonomers is under study [140]
in which both micellar and homogeneous nucleations by homo- and copolymerization
with macromonomer in the continuous phase are considered.
Another interesting heterogeneous polymerization using macromonomers is
a microemulsion copolymerization to produce particles 10–100 nm in diameter.
Gan and coworkers [150] have prepared transparent nanostructured polymeric
materials by direct polymerization of bicontinuous microemulsions consisting