Regiospecificity ethylene/propylene

The polymerization is highly regiospecific only head-to-tail einchained monomer units are detected in highly isotactic polymers and only odd methylene sequences are detected in ethylene/propylene copolymers (10-12). The insertion of all propylene units into the reactive metal-carbon bond is primary (or antimarkownikow)... 

The presence of head-to-head" and tail-to-tail units in addition to the head-to-tail ones in propylene homopolymers (11,32), and of a number of even methylene sequences in ethylene/propylene copolymers (11,31,33-35) denotes lack of regiospecificity. As a consequence the syndiotactic polymerization of propylene is conveniently described as a binary copolymerization (11, 31, 36) between head-to-tail" and "tail-to-he ad oriented monomer molecules ... 

To achieve absolutely regiospecific sulfonation, the diene inner blocks have been hydrogenated to yield a frilly saturated poly(ethylene-alt-propylene) elastomer, in the case of isoprene, and poly(ethylene-co-l-butene) in the case of butadiene. Due to ease of the linking reaction, most of the latest work has dealt with polybutadiene-based samples, and the remaining discussion will deal with them, although the reactions and techniques are also applicable to the polyisoprene-based samples. 

Although ordinary metallocenes are inactive for styrene polymerization, certain metallocenes can be effective for ethylene/styrene copolymerization [20-23]. Oliva et al. reported that the regiospecificity of styrene insertion into the Zr- CHs bonds is predominantly secondary in ethylene/styrene copolymerization using the [Me(Ph)C(fluorenyl)(Cp)]ZrCl2-MAO catalyst system [20]. Oliva later presented that some styrene units can be introduced in an isotactic polypropylene sequence (1,2-insertion) by using a small amount of ethylene to reactivate the catalyst after the styrene insertion (2,1-insertion) in propylene/styrene copolymerization using a r c-[Et(indenyl)2]ZrCl2-MAO catalyst system [21]. 

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