Regioirregular Propylene Insertion

SCHEME 1.4 (a) 2,1-Insertion following 1,2-insertion into a growing polymer chain and (b) isomerization to produce a 3,1-insertion. (Adapted with permission from Resconi, L. Cavallo, L. Fait, A. Piemontesi, F. Chem. Rev. 2000,100, 1253-1345. Copyright 2000 American Chemical Society.) 

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In summary, for copolymers having equivalent amounts and distributions of propylene comonomer units, a higher disturbance of PE crystallinity is achieved in the case of regio- and stereoirregular placements of propylene units. Moreover, both experimental data and calculations indicate that regioirregularity of propylene insertion is more effective in disturbing crystallinity than stereoirregularity. 

Catalysts based on the Hf pyridyl amine complexes 126-128 have been used for the preparation of ethylene/ propylene co-polymers as well as of ethylene/propylene/l-octene terpolymers. These co-polymers are characterized by having at least 60 wt% propylene units, Mw around 300000, and Mw/Mn in the range 2.0-2.4. The NMR analysis of these co-polymers showed that the propylene sequences are remarkably isotactic mm > 90%) and showed the presence of regioirregularly inserted propylene units(<0.5% mol). The most interesting property of catalysts based on 126-128 is their high thermal stability.1119 Using modifications of isospecific bis(phenoxy-amine)-based catalysts, such as complex 164, the controlled synthesis of iPP- /orjf-poly/E-co-P) diblock co-poly-mers has been achieved. This is a remarkable result since iPP and PE are both polymeric materials of extreme industrial relevance.1206... 

Insertion of propylene with 1,2-regioselectivity is known as primary insertion or regioregular insertion because it is the most prevalent type of monomer enchainment for metallocenes. Some metallocenes do insert propylene in other, regioirregular ways (Scheme 1.4). The monomer may be inserted with 2,1-regioselectivity (Scheme 1.4a), known as secondary insertion, with the more substituted olefinic carbon bonded to the metal. Following 2,1-insertion, a unimolecular isomerization may take place to give a 3,1 -insertion (Scheme 1.4b). Alternatively, monomer insertion can... 

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