Elastomeric polypropylene homopolymers using metallocene catalysts

One of the most successful methods to produce ELPP directly has been reported extensively by DuPont researchers and involves the use of heterogeneous catalysts comprised of tetra-alkyl complexes of Group IVB transition metals of the general formula (MR4) on metal oxide sup- 

In 1990, Chien et at. [5] discovered the nonsymmetiical metallocene rac-[ethylidene(l -ir -tetramethylcyclopentadienyl)(l-T) -indenyl)I titanium(IV)dichloride (1) with methylaluminoxane (MAO) as cocatalyst 

In both instances, the microstructure of ELPP produced using stereo-rigid metallocenes could not be fully accounted for using a simple migratory insertion model of propagation. Collins proposed a chain 

It might be expected that an ELPP with a block-type microstructure would display a relationship between %mmmm pentad intensity and polymer melting temperature somewhat intermediate between the blended samples and the compositionally pure, pseudorandom microstructures produced using stereorigid metallocenes. This finding supports Waymouth s contention that a very different propagation process is occurring with their catalyst system. 

For an elegant overview of propylene polymerizations, see Albizzati, E., Giannini, U., Collina, G., Noristi, ,., Resconi, L. (1996) Polypropylene Handbook (ed. E.P. Moore), Hanser, Munich. 

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Interestingly, aPP found less use in blends with thermoplastic polymers irrespective of the high number of related patents. The new generation aPP, produced by metallocene synthesis, may change this scenario (see also the chapter Elastomeric polypropylene homopolymers using metallocene catalysts ). Blending of HMW-aPP with polyolefins may result in a new mechanical property profile, e.g. rubberlike resilience. Such products may compete with those made of flexible PVC. 

Elastomeric polypropylene homopolymers using metallocene catalysts... 

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