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

146 K. Ito, S. Kawaguchi
Fig. 3. Model of cross-propagation between a grafted poly(comonomer) radical and a macromonomer
In some but not so rare cases, however, reactivity of macromonomers was
found to be apparently reduced by the nature of their polymer chains. For example,
p-vinylbenzyl- or methacrylate-ended PEO macromonomers, 26 (m=1) or
27b, were found to copolymerize with styrene (as A) in tetrahydrofuran with increasing
difficulty (1/r A is reduced to one half) with increasing chain length of
the PEO [41]. Since we are concerned with polymer-polymer reactions, as
shown in Fig. 3, the results suggest that any thermodynamically repulsive interaction,
which is usually observed between different, incompatible polymer
chains, in this case PEO and PSt chains, may retard their approach and hence the
reaction between their end groups, polystyryl radical and p-vinylbenzyl or
methacrylate group. Such an incompatibility effect was discussed in terms of the
degree of interpenetration and the interaction parameters between unlike polymers
to support the observed reduction in the macromonomers copolymerization
reactivity [31, 40]. Similar observations of reduction of the copolymerization
reactivity of macromonomers have recently been reported for the PEO macromonomers,
27a (m=11) with styrene in benzene [42], 27b with acrylamide in
water [43], and for poly(L-lactide), 28, with dimethyl acrylamide or N-vinylpyrrolidone
in dioxane [44].
(28)
The composition distribution of the graft copolymers obtained by the macromonomer
method has been shown theoretically to be statistically broader
than in the corresponding conventional linear copolymer, due to the high MW
of the macromonomer branches [45, 46]. This has been experimentally confirmed
by Teramachi et al. with PSt macromonomers, 23 or 24, copolymerized
with MMA [47–49]. The chemical composition distribution was found to broad-