glance at the data given in Tables 1, 2, 7, and 8 reveals that the introduction of tertbutyl groups in positions 3 and 6 of the fluorenyl moiety of the ligand causes
substantial improvements with respect to enantio- and stereoselectivity of the
resulting catalysts 9/MAO and the stereoregularity of the s-PP polymers it
produces. The data presented in Table 8, compares the microtacticity variations
of 1 and 9 under changing polymerization temperatures.
The data clearly shows, as anticipated, a substantial decrease in rmmr pentad
concentrations related to meso triad (mm) stereoerrors in the backbone of syndiotactic
polymer chains produced with 9/MAO compared to the corresponding polymers
produced with 1/MAO at comparable polymerization temperatures. Interestingly,
even the rrmr pentad concentrations in polymers produced with 9/MAO, directly
proportional to the catalyst’s site epimerization frequency, are lower than
the observed rrmr pentad concentration for polymers produced with 1 (and 6). For
syndiotactic polymers produced with both catalyst systems, the rrmr pentad
concentrations almost double with every 20
C increase in polymerization temperature
with the same rate. On the other hand, the enantiomorphic site control related rmmr
pentad concentrations in syndiotactic polymers produced at different temperatures
Table 7 Polymerization results, polymer analysis, and stereodefects generated in the polymers
produced with 9/MAO at different polymerization temperatures
Temperature (
C)
M W (kDa)
rrrr (%)
rmmr (%)
rrmr (%)
Melting point (
C)
40
766
91.0
0.73
0.93
150
60
590
88.5
0.85
1.65
143
80
443
79.0
1.06
3.79
128
Table 8 Comparison of
13
C NMR normalized spectroscopic stereosequence distributions (%) of
syndiotactic polypropylene samples produced with 1/MAO and 9/MAO at different polymerization temperatures
Temperature (
C)
9/MAO catalyst system
1/MAO catalyst system
rmmr (%)
rrmr (%)
rmmr (%)
rrmr (%)
40
0.73
0.93
1.55
1.15
60
0.85
1.99
1.65
2.70
80
1.06
3.79
2.20
4.82
Fig. 15 Two perspective views of the single-crystal X-ray determined molecular structure of
(η
5
-C 5 H 4 -μ-CPh 2 -η
5
-3,6-dit Bu-C 13 H 6 )ZrCl 2 , 9 [28–30]
Syndiotactic Polypropylene: Discovery, Development, and Industrialization. . .
71
substantial improvements with respect to enantio- and stereoselectivity of the
resulting catalysts 9/MAO and the stereoregularity of the s-PP polymers it
produces. The data presented in Table 8, compares the microtacticity variations
of 1 and 9 under changing polymerization temperatures.
The data clearly shows, as anticipated, a substantial decrease in rmmr pentad
concentrations related to meso triad (mm) stereoerrors in the backbone of syndiotactic
polymer chains produced with 9/MAO compared to the corresponding polymers
produced with 1/MAO at comparable polymerization temperatures. Interestingly,
even the rrmr pentad concentrations in polymers produced with 9/MAO, directly
proportional to the catalyst’s site epimerization frequency, are lower than
the observed rrmr pentad concentration for polymers produced with 1 (and 6). For
syndiotactic polymers produced with both catalyst systems, the rrmr pentad
concentrations almost double with every 20
C increase in polymerization temperature
with the same rate. On the other hand, the enantiomorphic site control related rmmr
pentad concentrations in syndiotactic polymers produced at different temperatures
Table 7 Polymerization results, polymer analysis, and stereodefects generated in the polymers
produced with 9/MAO at different polymerization temperatures
Temperature (
C)
M W (kDa)
rrrr (%)
rmmr (%)
rrmr (%)
Melting point (
C)
40
766
91.0
0.73
0.93
150
60
590
88.5
0.85
1.65
143
80
443
79.0
1.06
3.79
128
Table 8 Comparison of
13
C NMR normalized spectroscopic stereosequence distributions (%) of
syndiotactic polypropylene samples produced with 1/MAO and 9/MAO at different polymerization temperatures
Temperature (
C)
9/MAO catalyst system
1/MAO catalyst system
rmmr (%)
rrmr (%)
rmmr (%)
rrmr (%)
40
0.73
0.93
1.55
1.15
60
0.85
1.99
1.65
2.70
80
1.06
3.79
2.20
4.82
Fig. 15 Two perspective views of the single-crystal X-ray determined molecular structure of
(η
5
-C 5 H 4 -μ-CPh 2 -η
5
-3,6-dit Bu-C 13 H 6 )ZrCl 2 , 9 [28–30]
Syndiotactic Polypropylene: Discovery, Development, and Industrialization. . .
71