Propylene Polymerization with Sterically Hindered Unbridged 2-Arylindene Metallocenes

Abstract

Metallocene catalyst systems derived from bis(2-phenylindenyl)zirconium dichloride (1) yield elastomeric polypropylenes of low to intermediate tacticity. The sterically hindered metallocene bis(2-(3,5-di-tert-butylphenyl)indenyl)zirconium dichloride (2) produces polypropylenes of much higher isotacticity than 1 ([mmmm] ) 78% vs 44% in liquid propylene). Kinetic profiles of polymerizations conducted with 1/MMAO and 2/MMAO reveal that the initial rates of polymerization increase with increasing temperature; the activity of both catalysts decreases with time, but the decrease is less pronounced for 2/MMAO than for 1/MMAO. The polymer microstructure is highly dependent upon polymerization conditions: isotacticity decreases with increasing temperature and decreasing monomer concentration. Lower tacticity polypropylenes ([mmmm] ) 40%) generated with 2/MMAO at low monomer concentrations contain a high percentage of [mmrm] stereoerrors, which is indicative of a stereoblock microstructure comprised of isotactic stereosequences of opposite relative configuration. Activation of bis(2-(3,5-di-tertbutylphenyl)indenyl)zirconium dimethyl (3) with [Ph 3C][B(C6F5)4] (4) or B(C6F5)3 (5) yielded catalysts with quite different polymerization behavior. A modest drop in productivity and isotacticity in propylene polymerization is observed when 3 is activated with 4, relative to MMAO, but catalysts derived from 3/B(C6F5)3 exhibited low productivity and afforded amorphous polypropylenes of very low tacticity ([mmmm] ) 12%).

Oscillating Non‐Metallocenes – from Stereoblock‐Isotactic Polypropylene to Isotactic Polypropylene via Zirconium and Hafnium Dithiodiphenolate Catalysts

“…Further NMR spectroscopic investigations revealed that the microstructure of the polypropylene depended on the nature of the aryl group: [7] catalysts featuring nonsubstituted aryl groups led to mixtures of polymers containing isotactic blocks separated by short stereo-irregular blocks, whereas catalysts featuring bulky aryl substituents led to polypropylene with isotacticstereoblock microstructure consistent with interconverting catalyst enantiomers. [7,8] nantly stereoblock-isotactic microstructure or predominantly isotactic microstructure could be obtained by varying the polymerization conditions. Long isotactic blocks of 50 to more than 100 repeat units were formed at -10°C in liquid propylene.…”

Systematic investigations of fatigue crack growth behavior of a PE‐HD pipe grade in through‐thickness direction

“…The developmental activities of well‐defined transition metal catalysts capable of initiating stereospecific living propylene polymerization have been intense in the past three decades, because these catalysts may provide potentially high‐performance polymers such as monodisperse polypropylenes (PPs) with high melting temperatures ( T m s) and block copolymers containing high T m segment. Besides numerous catalysts capable of highly stereospecific polymerization of propylene,1–17 recent progress in the rational design of well‐defined catalysts for olefin polymerization has resulted in the discovery of a growing number of catalysts for living propylene polymerization 18–52. For example, biscyclopentadienyl metallocene,18 diamine bisphenolate zirconium complexes,19, 20 fluorinated bis(phenoxyketimine)titanium complexes,21–23 α‐diimine Ni(II)24 complexes, and monocyclopentadienyl zirconiumn complexes25 are able to catalyze propylene polymerization in a living manner.…”

Propylene Polymerization with 1,2‘-Bridged Bis(indenyl)zirconium Dichlorides

“…As previously discussed by us and others, 28,29,49-51 polypropylenes derived from (2PhInd) 2 ZrCl 2 generate a range of stereoerrors, including those of types A, B, and C. Stereoerrors of type A are consistent with enantiomorphic site control errors and are expected for any conformation that is not completely stereoselective. Stereoerrors of type B have been proposed to arise from a conformational interconversion between two stereoselective anti conformations A and B (Scheme 1), 28,29,[49][50][51] and stereoerrors of type C are consistent with atactic stereosequences. These differences in sequence distributions as measured by NMR spectroscopy are also manifested in the thermal properties of these two polypropylenes: the highest melting point observed for the polypropylene derived from 3 is 97°C, whereas PP1-HI exhibits a melting point as high as 141°C.…”

“…Some of these low-tacticity polypropylenes have elastomeric properties and yet retain the high melting temperatures of more crystalline isotactic polypropylenes. 13,28,29,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] The interconversion of the metallocenes between stereoselective and nonstereoselective conformations at a rate comparable to chain propagation has been proposed as a possible mechanism for generating stereoblock polypropylene microstructures (Scheme 1). We have proposed that the anti rotamer generates isotactic sequences and the syn-oriented conformation is responsible for the observed atactic sequences, 27 although others have questioned the role of the syn isomers as a source of atactic stereosequences.…”

“…The polymerization behavior of these metallocenes illuminates the role of ligand substituents and bridge type on stereospecificity as well as productivity for this class of metallocenes and provides some insight into the polymerization behavior of gauche rotamers of unbridged, conformationally dynamic bis-(2-arylindenyl)metallocene systems. 13,28,29,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] …”