Hou reported the first example of efficient COC synthesis by rare earth metal
catalysts. Cationic rare earth (group 3 and lanthanide) metal alkyls is an emerging
new class of catalysts for the polymerization and copolymerization of various olefins,
including cyclic olefins [80, 81]. The combination of half-sandwich scandium bis
(alkyl) complexes such as Sc(η
5
-Cp)(CH 2 SiMe 3 ) 2 (THF) (for VIII-1, Cp ¼
C 5 Me 4 SiMe 3 ; VIII-2, Cp ¼ 1,3-C 5 H 3 (SiMe 3 ) 2 ; VIII-3, Cp ¼ C 5 Me 5 ) with 1 equivalent of a borate compound such as [Ph 3 C][B(C 6 F 5 ) 4 ] showed excellent activity for
E–N copolymerization [82]. Under appropriate conditions (25
C and 1 atm ethene),
the [Sc(η
5
-C 5 Me 4 SiMe 3 )(CH 2 SiMe 3 ) 2 (THF)]/[Ph 3 C][B(C 6 F 5 ) 4 ] system afforded an
amorphous alternating E–N copolymer with M n ¼ 85,000 g/mol, M w /M n ¼ 2.19,
T g ¼ 118
C, and norbornene content of 44 mol%, with an activity as high as
25,200 kg/(mol Sc h).
The catalytic properties of the following half-sandwich bis(alkyl) rare earth
complexes [Ln(η
5 -C 5 Me 4 SiMe 2 R)(η
1 -CH 2 SiMe 3 ) 2 (THF)] (Ln ¼ Sc, R ¼ Me;
Ln ¼ Sc, R ¼ C 6 F 5 ; Ln ¼ Y, R ¼ C 6 F 5 ; Ln ¼ Lu, R ¼ C 6 F 5 ) activated by [Ph 3 C]
[B(C 6 F 5 ) 4 ] in copolymerization of ethylene with norbornene have been assessed
by Ravasio et al. [83]. Both excellent activities and noticeable control in molar
mass distributions were found. Copolymer microstructure has been elucidated at
the tetrad level.
Detailed information on copolymerization mechanisms was obtained by Tritto
et al. [88] by calculating the E–N reactivity ratios employing a computer optimization routine, which allows the best fit to be obtained for the microstructural analysis
by
13 C NMR spectra. The theoretical equations relating copolymer composition and
feed composition were fitted to the corresponding experimental data. The reactivity
ratios for both first- and second-order Markov models (M1 and M2, respectively)
were derived. The reactivity values agree with the reports that E–N copolymers
obtained with IV-1/MAO are mainly alternating (r 1 Â r 2 ( 1), the norbornene
diad fraction is very low, and there are no norbornene triads or longer blocks
(r 2 % 0).
The ranges of the reactivity ratios obtained at the lowest [N]/[E] feed ratio are
r 1 ¼ 2.34–4.99 and r 2 ¼ 0.0–0.062. The r 2 values are in general smaller than those
obtained for propene copolymerization. The highest r 1 Â r 2 values found for the
copolymers prepared with catalyst I-4 confirmed its tendency to give more random
copolymers. The values of r 1 , r 2 , and r 1 Â r 2 for the E–N copolymers obtained with
catalysts IV-1 and I-5 are comparable with those of alternating ethene–propene
copolymers with metallocene catalysts. The results of the second-order Markov
model also showed that all r 11 values, as r 1 , are similar to those found for ethene and
propene copolymerization with metallocene catalysts with low reactivity ratios.
Differences in r 12 and in r 22 are illuminating, since they clearly show the preference
of the insertion of ethene or norbornene into E–N–Mt (Mt ¼ Metal) and N–N–Mt,
respectively. Parameter r 12 increases in the order IV-1 < I-5 ( I-1 < I-2, opposite
to the tendency to alternate the two comonomers [88].
Poly(E-co-N) 1 -b-poly(E-co-N) 2 and PE-b-poly(E-co-N), and thus new materials
consisting of crystalline and amorphous segments that are chemically linked, were
successfully synthesized with PI catalysts [90], rare earth catalysts [82], and
fluorinated enolato-imine titanium catalysts [91].
Polyolefins with Cyclic Comonomers
127
catalysts. Cationic rare earth (group 3 and lanthanide) metal alkyls is an emerging
new class of catalysts for the polymerization and copolymerization of various olefins,
including cyclic olefins [80, 81]. The combination of half-sandwich scandium bis
(alkyl) complexes such as Sc(η
5
-Cp)(CH 2 SiMe 3 ) 2 (THF) (for VIII-1, Cp ¼
C 5 Me 4 SiMe 3 ; VIII-2, Cp ¼ 1,3-C 5 H 3 (SiMe 3 ) 2 ; VIII-3, Cp ¼ C 5 Me 5 ) with 1 equivalent of a borate compound such as [Ph 3 C][B(C 6 F 5 ) 4 ] showed excellent activity for
E–N copolymerization [82]. Under appropriate conditions (25
C and 1 atm ethene),
the [Sc(η
5
-C 5 Me 4 SiMe 3 )(CH 2 SiMe 3 ) 2 (THF)]/[Ph 3 C][B(C 6 F 5 ) 4 ] system afforded an
amorphous alternating E–N copolymer with M n ¼ 85,000 g/mol, M w /M n ¼ 2.19,
T g ¼ 118
C, and norbornene content of 44 mol%, with an activity as high as
25,200 kg/(mol Sc h).
The catalytic properties of the following half-sandwich bis(alkyl) rare earth
complexes [Ln(η
5 -C 5 Me 4 SiMe 2 R)(η
1 -CH 2 SiMe 3 ) 2 (THF)] (Ln ¼ Sc, R ¼ Me;
Ln ¼ Sc, R ¼ C 6 F 5 ; Ln ¼ Y, R ¼ C 6 F 5 ; Ln ¼ Lu, R ¼ C 6 F 5 ) activated by [Ph 3 C]
[B(C 6 F 5 ) 4 ] in copolymerization of ethylene with norbornene have been assessed
by Ravasio et al. [83]. Both excellent activities and noticeable control in molar
mass distributions were found. Copolymer microstructure has been elucidated at
the tetrad level.
Detailed information on copolymerization mechanisms was obtained by Tritto
et al. [88] by calculating the E–N reactivity ratios employing a computer optimization routine, which allows the best fit to be obtained for the microstructural analysis
by
13 C NMR spectra. The theoretical equations relating copolymer composition and
feed composition were fitted to the corresponding experimental data. The reactivity
ratios for both first- and second-order Markov models (M1 and M2, respectively)
were derived. The reactivity values agree with the reports that E–N copolymers
obtained with IV-1/MAO are mainly alternating (r 1 Â r 2 ( 1), the norbornene
diad fraction is very low, and there are no norbornene triads or longer blocks
(r 2 % 0).
The ranges of the reactivity ratios obtained at the lowest [N]/[E] feed ratio are
r 1 ¼ 2.34–4.99 and r 2 ¼ 0.0–0.062. The r 2 values are in general smaller than those
obtained for propene copolymerization. The highest r 1 Â r 2 values found for the
copolymers prepared with catalyst I-4 confirmed its tendency to give more random
copolymers. The values of r 1 , r 2 , and r 1 Â r 2 for the E–N copolymers obtained with
catalysts IV-1 and I-5 are comparable with those of alternating ethene–propene
copolymers with metallocene catalysts. The results of the second-order Markov
model also showed that all r 11 values, as r 1 , are similar to those found for ethene and
propene copolymerization with metallocene catalysts with low reactivity ratios.
Differences in r 12 and in r 22 are illuminating, since they clearly show the preference
of the insertion of ethene or norbornene into E–N–Mt (Mt ¼ Metal) and N–N–Mt,
respectively. Parameter r 12 increases in the order IV-1 < I-5 ( I-1 < I-2, opposite
to the tendency to alternate the two comonomers [88].
Poly(E-co-N) 1 -b-poly(E-co-N) 2 and PE-b-poly(E-co-N), and thus new materials
consisting of crystalline and amorphous segments that are chemically linked, were
successfully synthesized with PI catalysts [90], rare earth catalysts [82], and
fluorinated enolato-imine titanium catalysts [91].
Polyolefins with Cyclic Comonomers
127