vinylidene

1. P = PP + ½ PE E = EE + ½ PE PP = Saa PE = Sag + Sad EE = ½(Sbd + Sad) +1/4 Sgd Tbb Pbb + Pbd +Pdd Saa Sag Tbd Tdd Sbb allyl 4-methyl-3-pentenyl vinylidene ETHENE-PROPENE COPOLYMERS WITH FLUORENYL-BASED METALLOCENE CATALYSTS M.Cornelio1,2, P.Locatelli1, G.Di Silvestro2, L.Boggioni1, I.Tritto1. 1 Istituto per lo studio delle Macromolecole, Consiglio Nazionale delle Ricerche, Via Bassini, 15, 20133, Milano. 2 Dipartimento di Chimica Organica e Industriale, Università degli Studi di Milano, Via Venezian, 21, 20133, Milano massimiliano.cornelio@ismac.cnr.it Methods Introduction Objectives • Propene homopolymers and propene-ethene copolymers have been synthesized ; • C1-symmetric (A and D) and the reference CpFlu metallocene precursors activated by MAO have been used; • The homo- and copolymers have been characterized by 1H and 13C-NMR and GPC to have an evaluation of the factors that affect the chain transfers and molar masses • The development of Cs-symmetric catalysts has opened the possibility to synthesize syndiotactic polypropylene (sPP): • Thermoplastic materials; • High melting point; • High cristallinity. Adding low amount of ethylene to sPP (1-5 mol %) a better plastic material could be obtained: • Higher cristallinity; • Higher elasticity; • Lower Molecular Weight The aim of the work is to study the influence of low amount of ethylene on the Mwof sPP obtained using C1- and Cs-symmetric metallocene precursors Cs C1: A and D Fig. 1 Cs- and the two C1-symmetric metallocene precursors: A: R substituent more hindered than in D Copolymers Homopolymers In Autoclave. Conditions: Solvent: 150 ml of Toluene; Al/Zr: 3000 m.r.; pressure: beetween 4-7 bars; ethylene: 0.5 mol% in feed. • The more hindered R substituent in A leads to the highest activity; • All the catalysts give mainly syndiotactic polypropylene; • The rrrr percentage decrease when T is increased; • The Mw decreases when the T is increased; • The more hindered R and R1 substituents in C1–symmetric catalysts leads to an increase in Mw with respect the reference CpFlu catalyst. • The more hindered R and R’ substituents in A leads to the highest activity; • The D catalyst incorporates high amount of ethylene; • The amount of comonomer incorporated increases when the T is increased; • The more hindered R and R1 substituent in C1–symmetric catalysts leads to an increase in Mw with respect the reference CpFlu catalyst; in any cases the Mw is influenced by theT and is lower than homopolymers. • The more hindered R and R’ substituents in A leads to the highest activity and to highest molar masses of Copolymers Chain termination mechanisms a) Left chain end groups b) Right chain end groups b-hydrogen transfer to metal b-hydrogen transfer to metal ethyl vinylidene vinylidene b-hydrogen transfer to monomer b-hydrogen transfer to monomer n-butyl vinylidene vinylidene Chain propagation Chain propagation n-propyl b-hydrogen transfer to metal allyl b-hydrogen transfer to monomer allyl b-CH3 abstraction allyl n-propyl Chain propagation 1H-NMR: left chain end groups 13C-NMR: right chain end groups vinylidene Homopolymers Copolymers Copolymer n-butyl allyl ethyl n-propyl • Ethyl>n-propyl groups with both Cs and C1-symmetric catalysts: chain transfer to ethylene is preferred; • High percentage of n-butyl groups with both catalysts: the reinitiation is preferred with an ethylene unit. • No terminal groups visible with A catalyst because of too high molecular weights. r D D • Homopolymers: percentage of vinylidene groups higher than allyl groups both by using Cs and C1-symmetric catalysts: theb-H transfer is preferred with respect the CH3-abstraction. • Copolymers: the very low percentage of allyl groups with respect the vinylidene groups: the termination is preferred after propylene unit insertions; Conclusions A • In the presence of less hindered ethene molecules the rate of -H transfer to ethene become kinetically competitive with respect the chain propagation pathway and thisresults in lower molecular weight. • The appropriate hindrance of the ligand in catalystA allows to minimize this effect which has a strong negative effect on the production and properties of the final copolymer material. • Ethene molecules can lead to an increase in activity due to the possibility of E insertion at dormant sites. • J.A. Ewen, R.L. Jonas, A. Razavi. J. Am. Chem. Soc, 1988, 110, 6255; • J. Voegele, C. Troll, B. Rieger. Macromol. Chem. Physics, 2002, 203, 1918 • D. Wang, S. Tomasi, A. Razavi, T. Ziegler. Organometallics, 2008, 27, 2861. • Carvill, I. Tritto, P. Locatelli, M. C. Sacchi. Macromol, 1997, 30, 7056