XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

1. Propene Polymerization Mechanisms By Using C1-Symmetric Catalysts M. Cornelio, L. Boggioni, I. Tritto, G. Di Silvestro ISMAC-CNR, Milano XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

2. 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 r r r r r J. Ewen, A. Razavi. J. Am. Chem. Soc., 1988, 1 IO, 6255 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

3. r r r r r m m r r m r r 13C-NMR: Homopolymers rrrrpentad: chainmigratorymechanism rmrr pentad: back skip insertion mechanism, skipped insertion; rmmrpentad: site control mechanism XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

4. 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 Cs C1 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. XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

5. 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 Macromolecole Terni 4-8 Settembre 2011

6. 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 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

7. 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 Macromolecole Terni 4-8 Settembre 2011

8. C1–Symmetric Catalysts Studied 1 3 2 Compared to 4 5 C1 Cs XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

9. Homopolymerization Activity 1 2 3 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

10. 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 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

11. Statistical analysis • site epimerization (bold line) • alternating mechanism (plain line) • alternation between a perfectly stereoselective site with probability a = 1 and a variably stereoselective site with probability (1-a) = b= 1(left side) • alternation between two sites with probability a, b = 1 of various stereoselectivity (right side) XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

12. Analysis of PP by Reference Catalysts 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 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 Macromolecole Terni 4-8 Settembre 2011

13. Comparison among the catalysts desymetrization due to to the prensence of bulky group is slight leading to sPP yet. • Alternating mechanisms could predict the polypropylene microstructure • The presence of bulky t-but on fluorenyl renders: • Site epimerization slight more favorable • Alternating slight less favorable Cs C1 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

14. Increasing the T and monomer concentration: site epimerization becomes more favorable alternating mechanisms becomes less favorable XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

15. Comparison among the catalysts The presence of diphenyl bridge renders the site epimerization more favorable and the alternating mechanisms less favorable XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

16. The presence of second bulky group on Cp side of the metallocene leads to a iPP The r.m.s. error are similar for the three predictive mechanisms. Both the alternating and the site epimerization mechanisms are allowed. a and b have the same value

17. 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 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011

18. Conclusions 1 3 2 • Cat 1 and Cat 2: • alternating mechanisms prevail; • microstructure is dependent on monomer concentration and temperature. • Cat 3 • 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 XX Convegno Italiano di Scienza e Tecnologia delle Macromolecole Terni 4-8 Settembre 2011