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

Poly(macromonomers), Homo- and Copolymerization 167
Table 4. The power law exponents in dispersion copolymerization with PEO macromonomers,
R=K[Monomer] a [Macromonomer] b [Initiator] c
Macromonomer Monomer Medium a b c Ref.
theory, Eq. (27) 0.67 –0.50 –0.083
26, m=4, n=45
26, m=1, 4, 7,
n=53, 110
Styrene
BMA
MeOH+H2O(9:1) MeOH+H2O(8:2) 0.63 0.82 –0.52 –0.54 –0.068 –0.10 112
113
26, m=1, n=45
26, m=1, n=45
26, m=1, n=45
26, m=1, n=45
27a, m=11, n=40
MMA
MMA
MMA
MMA
Styrene
MeOH+H2O(8:2) MeOH+H2O(7:3) MeOH+H2O(6:4) MeOH+H2O(5:5) EtOH+H2O(9:1) –
0.85 –
–
1.02 –1.17 –1.15 –0.51 –0.52 –0.60 –
–0.030 –
–
–0.090 114
114
114
114
115
radius is quantitatively described by the model with reasonable constants, q =1,
r =1.05 g cm –3 , N A =6.02´10 23 , k 2 =10 9 l mol –1 s –1 , k p =352 l mol –1 s –1 , k t =
6.1´10 7 l mol –1 s –1 , k d =3.2´10 –7 s –1 , f=1, and S crit /r 1 =10 nm 2 , r 1 =1, where S crit
was calculated from Eq. (29) using the value of for PEO in methanol at
25 ˚C [131].
In the dispersion copolymerization with PEO macromonomers, the power
law exponents in Eq. (27) have been experimentally determined and compared,
as summarized in Table 4. Initial monomer concentration has a major influence
on the final particle radius. The experimental power law exponents (0.82–1.02)
is usually significantly larger than that in Eq. (27), except for 0.63 for styrene as
a monomer with 26 (m=4, n=45). This is likely to be due to a solvency effect of
the monomer. The values of the exponent of macromonomer and initiator concentration
dependence in the polymerization of hydrophobic monomer, styrene
and n-butyl methacrylate are in good agreement with those from Eq. (27). In remarkable
contrast, unusually high exponent values (ca. 1.2) have been obtained
in the dispersion copolymerization of a polar monomer, MMA in methanol-water
(8:2 and 7:3 v/v) media. The exponent value decreases down to 0.51, when the
water content is increased to higher than 40%. This significant change in the exponent
value with the polarity of the continuous phase cannot be simply explained
by the current theory and further refinement is needed.
6.3
Emulsion Polymerization
Emulsion polymerization is a free radical initiated chain polymerization in
which a monomer or a mixture of monomers is polymerized in aqueous solution
of a surfactant to form a product, known as a latex. The most important feature
of emulsion polymerization is its heterogeneity from the beginning to the end of
the polymerization, to yield in a batch process submicron-sized polymeric particles,
often of excellent monodispersity. The main ingredients for conducting