The anionic polymerizations of 4-, 3-, and
2-(3,3-dimethyl-1-butynyl)styrenes (3a, 3b,
and
3c), 4-, 3-, and 2-(1-hexynyl)styrenes (4a,
4b, and 4c), and 4-(phenylethynyl)styrene
(5) were carried out
in THF at −78 °C with oligo(α-methylstyryl)dipotassium
and sec-butyllithium. The polymerizations
of
these monomers proceeded quantitatively at −78 °C for 0.5 h.
The resulting polymers all possessed the
predicted molecular weights based on the molar ratios of monomer to
initiator and the narrow molecular
weight distributions
(M
w/M
n = 1.03−1.15).
The living character of the propagating carbanion
derived
from these monomers was further confirmed by the quantitative
initiation efficiency in the second-stage
polymerization. A variety of novel block copolymers with
well-defined chain structures were synthesized
by the sequential block copolymerization of 3a,
4a, 5, and
4-((trimethylsilyl)ethynyl)styrene (1a)
with
isoprene, styrene, 2-vinylpyridine, and tert-butyl
methacrylate. Furthermore, the relative reactivities
of
the monomers and the resultant living polymers were evaluated from the
results of the anionic block
copolymerizations. Higher reactivity of 3a,
4a, 5, and 1a and lower
nucleophilicity of their living polymers
were clearly demonstrated, compared with those of styrene and living
polystyrene, respectively. Both of
these features can be explained by the electron-withdrawing character
of the ethynyl substituents and
the extended π-conjugation system including the carbon−carbon
triple bond. The anionic polymerizabilities of 3a, 4a, 5, and
1a are estimated to be the same level of
2-vinylpyridine.
