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

142 K. Ito, S. Kawaguchi
4.1
Homopolymerization
Radical homopolymerization kinetics of some typical macromonomers, such as
those from PSt, 23, 24 [30, 31], and PMMA, 25 [32, 33], have been studied in detail
by means of ESR methods.
(23)
(24)
(25)
The kinetics apparently follow the conventional square-root equation for the
overall rate of polymerization, R p:
where k p and k t are the rate constants of propagation and termination, respectively,
k d and f are rate constants of initiator decomposition and initiation efficiency,
respectively, and [I] and [M] are the concentrations of initiator and monomer,
respectively. Therefore, we also have the conventional expression for the
kinetic chain length, n:
where DP n ˚ is an instantaneous number-average degree of polymerization assuming
no chain transfer and x is the fraction of disproportionation in the termination
step.
Table 1 [1] summarizes the relevant kinetic parameters. Clearly, the polymerization
of macromonomers, 23–25, is characterized by very low k t values and by
less reduced k p values, compared to those of the corresponding conventional
monomers such as styrene and MMA. This means that the propagation involving
the macromonomer and the multibranched radical is slightly less favored
(1)
(2)