xx convegno italiano di scienza e tecnologia delle macromolecole terni 4-8 settembre 2011

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


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


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


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.


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


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


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


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


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


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


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. (%)


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


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.


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. (%)


alternating = 1 1 0.054 1.66

alternating <1 0.972 0.025 1.52

T = 30° C r.m.s. (%)


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


T (°C) r.m.s. (%)


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. (%)


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


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.(%)


alternating =1 1 0.906 0.886

alternating <1 0.952 0.952 0.687

T = 50°C r.m.s.(%)


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


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 macromolecole terni 4-8 settembre 2011

Documents