1、FUDAN,Transition metal catalyzed olefin polymerization,Zieglers reactor,FUDAN,How important is the catalytic polymerization of olefin ?,Polyolefins: world production: 70 million tons (2003), 130 million tons (2009) 170 Million tons (2012) ca. 50% of the whole production of plastics. Mostly polymeriz

2、ed by Ziegler-Natta and metallocene catalysts.,Tailoring the structure of polyolefins is extremely Impor-tant to yield properties which can be used in various conditions. (some examples),Metallocene and late transition metal catalysts are powerful in controlling the structure of the resulting polyol

3、efins.,Research in both University and Company: thousands of patents and publications.,FUDAN,Ziegler-Natta Catalyst,1953: Ziegler, HDPE by AlRn/Transition TiCln at low pressure in the Mlheim Max Planck Institute for Coal Research,1954: Natta, Isotactic poly(-olefin) by the same mixture Milan Polytec

4、hnic,1954-: world-wide research and commercialization,“It is doubtful that it can be challenged by any other catalyst for its versatility.”,Huang, J.; Rempel, G. L. Prog. Polym. Sci. 1995, 20, 459-526,The year when Staudinger was awarded Nobel prize,FUDAN,Ziegler-Natta Catalyst,“Ziegler Natta cataly

5、sts became prominent in a special period in the history of polymer science, a period that not only produced many new commercial polymers but also enhanced our basic knowledge of polymer properties and structure as well as polymerization processes”.,Boor, J. Ziegler-Natta Catalysts and Polymerization

6、s, p.1 Academic Press, New York, 1979.,FUDAN,Nobel Prize for Ziegler-Natta,1963: “Nature synthesizes many stereoregular polymers, for example, cellulose and rubber. This ability has so far thought to be a monopoly of Nature operating with biocatalysts known as enzymes. But now professor Natta has br

7、oken this monopoly”.,Nobel e-Museum: http:/www.nobel.se/chemistry,FUDAN,Ziegler-Natta catalyst,Two components:,Compounds of group IV-VIII transition metal: TiCl4, TiR2Cl, VCl4, ZrCl4,Compounds of group I-III metal: AlEt3, Al-i-Bu3, AlEt2Cl, AlEtCl2, AlEt2OR,The third component: electron donors as re

8、activity promoter Amine, ether, etc.,FUDAN,MgCl2 Supported catalyst,The early situation: colored products due to metal residues, removal of solvents.,Breakthrough in catalyst engineering:,Z.-N./ MgCl2 with phthalates in 1960s Z.-N./ MgCl2 with diethers in 1990s,Advantages: very high activities; solv

9、ent free; controlled morphology of the final PP; possible for in-situ polymer alloys,Key point: well-defined microporous in catalyst.,FUDAN,MgCl2 supported catalyst,Basell Reactor Granule Technology:,BASF-Shell:,FUDAN,Stereospecificity,Consider a monosubstituted ethylene: CH2=CHR,The polymerization

10、leads to the formation of stereocenter at the tertiary carbons:,Consider a fully extended planar zigzag conformation, two different configurations are possible for each stereocenter. Note: it cannot tell which is R and which is S because we do not know the length at two sides of the center. They sho

11、uld be so and we name them in arbitrary,FUDAN,Stereospecificity,isotactic,syndiotactic,atactic,Stereospecific or stereoselective polymerization,FUDAN,Mechanism,The Cossee model:,Two steps: 1) complexation; 2) migratory insertion. The growing terminus flips from site to site,FUDAN,Mechanism,The trigg

12、er model by Ystenes:,FUDAN,Termination,Ziegler-Natta catalyst: living active site (lifetime hours) but non-living polymer chains (seconds to minutes). Therefore, each active site produces many polymer chains.,Termination by hydride to metal center:,or to monomer:,Termination by hydrogen (important i

13、n industry for MW control):,FUDAN,Nattas Nobel prize lecture,1963: The first highly stereoregular isotactic polymers were obtained in the presence of heterogeneous catalyst; however, it soon became clear that the heterogeneity of the catalyst is an essential factor for the polymerization of alphatic

14、 olefins to isotactic polymers, The vision was proved to be wrong after the discovery of metallocene catalyst.,FUDAN,Chronicle of the metallocene catalyst in olefin polymerization,1952, Determination of ferrocene structure; 1955, Metallocene as a component of Ziegler-Natta catalyst; Cp2TiCl2/AlR2Cl,

15、 homogenous Polymerization reactivity low: 104 g PE /(mol Ti hatm) 1973, Water effect: increasing activity; 1975, Kaminsky, tremendous increase in activity at larger amount of water; Cp2TiR2/AlR3 (halogen-free) 1976, Inspired by AlMe3/H2O, (BASF and Kaminsky, DE patent) MAO (methylaluminoxane) was p

16、repared; Cp2TiMe2/AlMe3/MAO: 107 g PE /(mol Ti hatm) but low stereospecificity. 1982, Synthesis of ansa metallocene with C2-symmetry by Brintzinger; 1984, isotactic polypropylene.,FUDAN,Why study metallocene ?,Homogenous solution; Single site active center; Lower polydispersity of the product; Unifo

17、rm incorporation of -olefin comonomers; Improved properties of the product: clarity, strength, etc.,The feature of metallocene catalysts: originally in order to better understand the mechansim of Z-N catalyst,FUDAN,Metallocene structure,Brintzinger: ansa-metallocene, the idea was once heavily critic

18、ized by his colleagues due to Nattas vision.,Traditional:,Constrained geometry catalyst,FUDAN,Metallocenes,Zirconocenes: mostly for ethene polymerization,X(Ind)2ZrCl2,X(Flu)(Cp)ZrCl2,X(Flu)2ZrCl2,FUDAN,What is MAO: the cocatalyst,Methylalumoxanes:,Possible structure:,network,linear,cyclic,The exact

19、structure is still unclear!,FUDAN,What is MAO: the cocatalyst,FUDAN,Function of the cocatalyst,2. The formation of the cationic metallocene complex:,3. Reactivation of inactive complexes formed by Hydrogen transfer reactions.,1. Alkylation of metallocene:,FUDAN,Feature of ethene polymerization,MW: 1

20、04 106 g/mol, depends on ratio of metallocene to monomer, temperature and the additional hydrogen. MWD: 3 Mixing of different metallocene: bimodal distribution Activity: much higher than Z.-N. catalyst Turnover: LLDPE: copolymerization of ethene and -olefin, uniform distribution,FUDAN,Dependence of

21、PE morphology on SCB,FUDAN,Propene polymerization,Regiospecificity: enchainment Head to tail, head to head, tail to tail Stereospecificity: stereoregularity, tacticity Atactic, syndiotactic, isotactic.,Two mechanisms of stereocontrol: 1. Catalytic site control: errors are corrected,2. Chain end cont

22、rol: stereoblock,FUDAN,Mechansim of polymerization,1. Chain propagation:,2. Chain termination and transfer:,FUDAN,amorphous,crystalline,crystalline, lowered melting point,crystalline,thermoplastic elastomer,atactic,isotactic,isotactic with irregularities,syndiotactic,isotactic-b-atactic,Tacticity of PP,FUDAN,Polymerization of cyclic olefins,FUDAN,Late transition metal catalyzed olefi