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XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
ISMAC-CNR, Milano
Propene Polymerization Mechanisms By Using
C1-Symmetric Catalysts
M. Cornelio, L. Boggioni, I. Tritto, G. Di Silvestro
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Cs Ansa-Metallocene:State of the Art
The development of Cs-symmetric catalysts by Ewen and Razavi has lead to the possibility to synthesized sPP
ZrP
ZrP
r r r r r
ZrZr
J. Ewen, A. Razavi. J. Am. Chem. Soc., 1988, 1 IO, 6255
13C-NMR: Homopolymers
r rr r
mr rm
r m r r
rrrr pentad: chain migratory mechanism
rmrr pentad: back skip insertion mechanism, skipped insertion;
rmmr pentad: site control mechanism
C ZrClMe
Me Cl
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
C1-Symmetric Ansa-Metallocene:State of the Art
The possibility to modify the ligand structure allows a high degree of control over polymer tacticity, molar masses and molar mass distribution
Many efforts have been done to understand the polymerization mechanism varying the bulkiness of the substituent on the ligands to improve the catalytic performances and the stereospecificity.
Cs C1
C ZrClMe
Me ClC Zr
R
MeMe Cl
Cl
R
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Homopolymer Microstructure
Class III catalysts: two-fold rotation axis; homotopic sites; isotactic
Class IV catalysts: vertical mirror plan; enantiotopic sites; syndiotactic
Class V catalysts: no symmetry elements; dastereotopic sites; not predictable
Di Silvestro, Farina.
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Homopolymer Microstructure By C1-Symmetric Catalysts
The homopolymer tacticity depends on the hindrance of the R-substituent on Cp group. Me hemi-isotactic polymer
i-Pr group atactic polymer
t-Bu group isotactic polymer
C ZrClMe
Me Cl
R
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Aims of The Work
to study propene homopolymerization with C1-symmetric catalyst with 1 or 2 substituents on the ligands
To study the influence of temperature and monomer concentration on the catalyst activities
to have a deep investigation on the polymerization mechanism
Methods All the homopolymers have been synthesized in experimental
conditions as close as possible to industrial conditions at three different temperatures
The homopolymers have been characterized by 13C-NMR at pentad level to determine the microstructure
A statistical study of the polypropene microstructure has been performed
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
C1–Symmetric Catalysts Studied
1 2 3
4 5
Compared to
CsC1
C Zr
t-But
ClPhPh Cl
C ZrClMe
Me Cl
C Zr
t-But
ClMeMe
t-But
ClC Zr
t-But
MeMe Cl
Cl
C ZrMeMe Cl
Cl
t-But
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Homopolymerization Activity
IN AUTOCLAVE
Temperature 30°, 50°, 70°C
Solvent 50 ml of Toluene
Propylene ~ 25 g
Co-Catalyst MAO
Al/Zr m.r. 3000 - 4000 m.r.
Catalysts 5 mol
Entry Catalyst T [Propene](molP/V)
Pressure(bar)
Activity(KgPP/molZr•h•P)
3 1 30 5.3 4.7 2780
4 1 50 12.0 10.5 1510
5 1 70 3.8 6.9 1026
6 2 30 12.5 7.7 1043
7 2 50 13.3 12.9 695
8 2 70 12.9 15.4 238
9 3 30 14.5 8.2 337
10 3 50 14.9 12.0 187
11 3 70 16.2 16,9 152
C Zr
t-But
ClPhPh Cl C Zr
t-But
ClMeMe
t-But
ClC Zr
t-But
MeMe Cl
Cl
2 31
0
500
1000
1500
2000
2500
3000
Act
ivit
y (K
gP
P/m
ol Z
r*h
*P)
30 50 70
Temperature (°C)
Cat 1
Cat 2
Cat 3
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
CatalystPressure
(bar)[Propene](molP/V) T (°C)
rrrr (%)
mmmm (%) rmrr (%) rmmr (%)
1 4.7 5.3 30 69.8 0.7 7.9 2.1
1 10.5 12.0 50 54.1 1.2 12.5 2.9
1 6.9 3.8 70 58.9 0.8 12.2 2.6
CatalystPressure
(bar)[Propene](molP/V) T (°C) rrrr (%) mmmm (%) rmrr (%) rmmr (%)
2 8.8 12.5 30 77.3 0.8 3.6 2.1
2 12.6 17.7 50 69.4 1.9 5.7 2.4
2 11.6 13.9 50 77.6 0.7 4.2 2.0
2 17.6 12.9 70 68.0 1.2 6.5 2.6
CatalystPressure
(bar)Propene](molP/V) T (°C) rrrr (%) mmmm (%) mrmm (%) mrrm (%)
3 8.2 14.5 30 0,6 86,9 0.7 1.71
3 12.0 14.9 50 1.3 88,8 1.2 1.7
3 16.9 16.2 70 0.8 84.0 1.9 2.1
1
2
3
Cat 1: mainly syndiotactic PP; rrrr pentad percentage decreases with T
Cat 2: highly syndiotactic PP; rrrr pentad percentage decreases with T and monomer concentration
Cat 3: highly isotactic PP; mmm pentad percentage is not dependent on T
C Zr
t-But
ClPhPh Cl
C Zr
t-But
ClMeMe
t-But
Cl
C Zr
t-But
MeMe Cl
Cl
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Statistical analysis
ZrPR
H
R
+
++
Zr
R
+
P
R
++
Zr
R
+H
PR
++
Zr
R
+P
R
++
si insertion
si insertion
site epimerization
more selective site less selective site
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
site epimerization (bold line)
alternating mechanism (plain line)
1. alternation between a perfectly stereoselective site with probability = 1 and a variably stereoselective site with probability (1- = = 1(left side)
2. alternation between two sites with probability of various stereoselectivity (right side)
T = 40°C r.m.s.(%)
site epimerization 0.952 0.687
alternating =1 1 0.906 0.886
alternating <1 0.952 0.952 0.687
Cs-symmetric catalyst:the alternating mechanisms better predict the polypropene microstructure
C1-symmetric catalyst:r.m.s error are similar for the three predictive mechanisms
C ZrClMe
Me Cl
T = 30°C r.m.s. (%)
site epimerization 0.631 29.45
alternating = 1 1 0.054 1.66
alternating <1 0.972 0.025 1.52
C ZrMeMe Cl
Cl
t-But
No conclusion was drawn concerning the mechanism since both alternating and site epimerizations could predict the microstructure
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Analysis of PP by Reference Catalysts
Alternating mechanisms could predict the polypropylene microstructureThe presence of bulky t-but on fluorenyl renders:
Site epimerization slight more favorable
Alternating slight less favorable
Comparison among the catalysts
CsC1
desymetrization due to to the prensence of bulky group is slight leading to sPP yet.
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
C Zr
t-But
MeMe Cl
Cl
CatalystPressure
(bar)[Propene](molP/V) T (°C) rrrr (%) mmmm (%) rmrr (%) rmmr (%)
2 8.8 12.5 30 77.3 0.8 3.6 2.1
2 11.6 13.9 50 77.6 0.7 4.2 2.0
2 17.6 12.9 70 68.0 1.2 6.5 2.6
T = 30°C r.m.s. (%)
site epimerization 0.631 29.45
alternating = 1 1 0.054 1.66
alternating <1 0.972 0.025 1.52
T = 30° C r.m.s. (%)
site epimerization 0.377 26.50
alternating = 1 1 0.091 2.72
alternating < 1 0.952 0.048 2.33
C Zr
t-But
MeMe Cl
Cl C ZrClMe
Me Cl
[P] = 12.5 M T (°C) r.m.s. (%)
site epimerization30 0.377 / 26.50
50 0.379 / 26.57
70 0.379 / 24.55
alternating = 130 1 0.091 2.72
50 1 0.090 2.71
70 1 0.131 3.88
alternating < 130 0.952 0.048 2.33
50 0.953 0.048 2.32
70 0.929 0.073 3.11
T = 50 °C [P] (mol/l)
r.m.s. (%)
Site epimerization 12.5 0.379 / 26.57
Site epimerization 17.0 0.376 / 25.07
alternating = 1 12.5 1 0.09 2.71
alternating = 1 17.0 1 0.13 4.03
alternating 1 12.5 0.953 0.048 2.32
alternating 1 17.0 0.932 0.048 3.27
Increasing the T and monomer concentration:site epimerization becomes more favorable alternating mechanisms becomes less favorable
C Zr
t-But
MeMe Cl
Cl
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
T (°C) r.m.s. (%)
site epimerization30 0.377 / 26.50
50 0.379 / 26.57
70 0.379 / 24.55
alternating =130 1 0.091 2.72
50 1 0.090 2.71
70 1 0.131 3.88
alternating <130 0.952 0.048 2.33
50 0.953 0.048 2.32
70 0.929 0.073 3.11
T (°C) r.m.s. (%)
site epimerization30 0.5 / 23.65
50 0.5 / 17.86
70 0.5 / 20.89
alternating =130 1 0.121 4.30
50 1 0.198 6.88
70 1 0.102 4.75
alternating <130 0.933 0.067 3.57
50 0.881 0.121 4.87
70 0.898 0.067 4.75
Comparison among the catalysts
The presence of diphenyl bridge renders the site epimerization more favorable and the alternating mechanisms less favorable
C Zr
t-But
ClPhPh Cl
C Zr
t-But
MeMe Cl
Cl
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Catalyst
Pressure
(bar)
T (°C)
rrrr (%)
mmmm (%)
mrmm (%)
mrrm (%)
3 8.2 30 0,6 86,9 0.7 1.71
3 12.0 50 1.3 88,8 1.2 1.7
3 16.9 70 0.8 84.0 1.9 2.1
C Zr
t-But
ClMeMe
t-But
Cl
T = 40°C r.m.s.(%)
site epimerization 0.952 0.687
alternating =1 1 0.906 0.886
alternating <1 0.952 0.952 0.687
T = 50°C r.m.s.(%)
site epimerization 0.975 0.652
alternating =1 1 0.924 0.891
alternating <1 0.975 0.975 0.651
C ZrMeMe Cl
Cl
t-But
The presence of second bulky group on Cp side of the metallocene leads to a iPP
C Zr
t-But
ClMeMe
t-But
Cl
The r.m.s. error are similar for the three predictive mechanisms.
Both the alternating and the site epimerization mechanisms are allowed.
and have the same value
The Cosse’s alternating mechanism occurs but back skip of the polymer chain to original position is necessary due to the presence of two bulky groups on the same half space
ZrPR
H
R
+
++
Zr
R
+
P
R
++
Zr
R
+P
R
++
si insertion
site epimerization
more selective site
si insertion
Zr
R
+H
PR
++
less selective site
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011
Conclusions
1 2 3
Cat 1 and Cat 2:
1. alternating mechanisms prevail;
2. microstructure is dependent on monomer concentration and temperature.
Cat 3
1. The alternating mechanisms seem to be the most probable but the site epimerization is necessary due to the presence of bulky groups on the same half-space of the growing polymer chain
C Zr
t-But
ClPhPh Cl
C Zr
t-But
ClMeMe
t-But
ClC Zr
t-But
MeMe Cl
Cl
XX Convegno Italiano di Scienza e Tecnologia delle MacromolecoleTerni 4-8 Settembre 2011