The copolymerization of ethylene with conjugated dienes such as isoprene and butadiene catalyzed by the half-sandwich scandium complexes (C
5
Me
4
SiMe
3
)Sc(CH
2
C
6
H
4
NMe
2
-
o
)
2
(
1
) and (C
5
Me
4
SiMe
3
) Sc(CH
2
SiMe
3
)
2
(THF) (
2
) has been detailedly studied. Microstructures and thermal properties of the copolymers obtained were characterized by NMR
GPC and DSC. Results showed that ethylene could be copolymerized with either isoprene or butadiene under 1.01 × 10
5
Pa of ethylene
and the copolymerization activity both reached up to 10
5
g polymer mol
Sc
−1
h
−1
at room temperature. The ethylene-isoprene and ethylene-butadiene copolymers with controllable compositions (ethylene content = 32 mol% − 79 mol%)
high molecular weight (
M
n
= 8.0 × 10
4
~ 19.7 × 10
4
)
and narrow molecular weight distribution (
M
w
/
M
n
= 1.11 − 1.32) were readily obtained by changing the feed ratio of isoprene or butadiene. The structures of catalysts and conjugated dienes could exert significant effects on the stereoselectivity and comonomer distribution sequences in the resulting copolymers. For the copolymerization of ethylene and isoprene
scandium complex
1
afforded multiblock ethylene-isoprene copolymers with different isoprene contents but a predominant 3
4-structure. These copolymers exhibited a glass transition temperature (
T
g
about −16 °C) and a melting temperature
(
T
m
127 °C)
which originated from the attributes of polyisoprene blocks and polyethylene blocks
respectively. Scandium complex
2
could give alternating ethylene-isoprene copolymers or random ethylene-isoprene copolymers with polyethylene blocks and isolated isoprene units at high or low amount of isoprene monomer used
and the isoprene in these copolymers mainly existed in 3
4-structure and
trans
-1
4-structure. The ethylene-isoprene alternating copolymers only showed a
T
g
at −46 °C
but as the isoprene content was lower than 32 mol%
T
m
that derived from polyethylene blocks appeared at 130 °C while
T
g
of −46 °C still existed due to the ethylene-isoprene alternating structures. As for the copolymerization of ethylene and butadiene
both scandium complexes
1
and
2
afforded multiblock ethylene-butadiene copolymers with different butadiene contents and predominant
cis
-1
4-structure
whereas the random degree of sequence distributions in copolymers prepared by
2
was higher than that in copolymers prepared by
1
. Moreover
these ethylene-butadiene copolymers displayed
T
g
s (−98 °C) and
T
m
s (71 − 125 °C) simultaneously
which were ascribed to polybutadiene blocks and polyethylene blocks
respectively.
关键词
钪乙烯异戊二烯丁二烯共聚合
Keywords
ScandiumEthyleneIsopreneButadieneCopolymerization
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