Stereoblock polypropylene synthesis catalysts

Rieger has recently reported another class of Ci catalysts (45) for the synthesis of stereoblock polypropylenes. However unlike the polymers formed using 42—44, polymers ranging from flexible plastics (with melting points as high as 134 °C) to thermoplastic elastomers are produced. Similar metallocenes... 

These results show that using catalyst 9a for polypropylene synthesis results in isotactic polypropylenes not in the manner of stereoblock polymers, but as iPPs with statistically distributed stereoerrors. 

The catalyst structures presented in the previous section have been used to prepare many types of polyolefins. The following several sections of this chapter provide an overview of the synthesis of polypropylenes containing various microstructures. These sections describe a selection of the catalysts that have been used to generate isotactic, syndiotactic, hemiisotactic, and stereoblock copolymers. Subsequent sections of this chapter describe catalysts that give rise to various copolymers of ethylene and propylene. Again, representative examples are provided, and the reader should consult other sources for comprehensive coverage of the synthesis and properties of each type of copolymer. ... 

Collette, J. W. Tullock, C. W. MacDonald, R. N. Buck, W. H. Su, A. C. L. Harrell, J. R. Mulhaupt, R. Anderson, B. C. Elastomeric polypropylenes from alumina-supported tetraalkyl group IVB catalysts. 1. Synthesis and properties of high molecular weight stereoblock homopolymers. Macromolecules 1989, 22, 3851-3858. 

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