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

Poly(macromonomers), Homo- and Copolymerization 145
Conventional radical polymerization usually produces polymers with a broad
distribution in DP. The polymers are mixtures of the instantaneous polymers
with DP w /DP n of at least 1.5 for the termination by recombination or 2.0 either
for the termination by disproportionation or for the chain transfer to small molecules.
In this respect, any living polymerization with rapid initiation will afford
polymers with a narrow DP distribution of the Poisson type. Ring-opening methathesis
polymerization of norbornenyl-terminated macromonomers, 8, 15,
and 16, appears promising in this regard [22, 23].
4.2
Copolymerization
A number of copolymerizations involving macromonomer(s) have been studied
and almost invariably treated according to the terminal model, Mayo-Lewis
equation, or its simplified model [39]. The Mayo-Lewis equation relates the instantaneous
compositions of the monomer mixture to the copolymer composition:
where d[A]/d[B] is the molar ratio of the monomers A to B incorporated into the
copolymers instantaneously formed from the monomer mixture with the molar
ratio [A]/[B], and r A and r B are the respective monomer reactivity ratios.
Copolymerization between a conventional comonomer (A) and a macromonomer
(B) affords a so-called graft copolymer with A as a backbone and B as statistically
distributed branches, as in Fig. 1b,d. Since usually [A]/[B]>>1 in order
to obtain a balanced composition (in weight) of backbone and branches, Eq. (3)
is approximated to a simplified form:
Therefore, the copolymer composition or the frequency of the branches is essentially
determined by the monomer composition and the monomer reactivity
ratio of the comonomer.
The relative reactivity of the macromonomer in copolymerization with a
common comonomer, A, can be assessed by 1/r A =k AB /k AA , i.e., the rate constant
of propagation of macromonomer B relative to that of the monomer A toward a
common poly-A radical. In summarizing a number of monomer reactivity ratios
in solution copolymerization systems reported so far [3, 31, 40], it appears
reasonable to say that the reactivities of macromonomers are similar to those of
the corresponding small monomers, i.e., they are largely determined by the nature
of their polymerizing end-group, i.e., essentially by their chemical reactivity.
(3)
(4)