Hemitactic polymers

An analogous method was used to obtain a new class of macromolecular stereoisomers The hemitactic polymers (99-101). This term refers to a head-to-tail vinyl polymer in which the tertiary carbon atoms constitute two distinct series one, which includes monomer units 1,3,5, 7,..., possesses strict steric regularity, whereas the other, with monomer units 2, 4, 6, 8,. .., is completely at random. In such polymers only one in every two tertiary atoms is influenced by an ordering rule 58 and 59 show the schematic structure of the hemiisotactic and hemisyndiotactic polymers where the white circles indicate the positions of disordered s ubstituents. The hemiisotactic polypropylene was obtained by Farina, Di Silvestro, Sozzani and Savar6 (99, 101) by nonste-reoselective reduction,of. isotactic frans-l,4-poly-2-methylpentadiene. 

A cyclopentadienyl, indenyl-ethane ligand undergoes insertion altematingly in an isotactic and an atactic fashion to give a hemitactic polymer, as is to be expected. 

Their potential to polymerize prochiral olefins, such as propylene, to give stereospecific polymers (isotactic. syndiotactic. hemitactic polypropylene). This variety opens the door to polyolefin elastomers. 

Tacticities of the polymers were estimated. For example, poly (1.3-pentadiene) was highly isotactic in the channels of perhydrotriphenylene, while it was preferentially isotactic (mesoiracemic = 2 1) in the channels of deoxycholic acid. A completely isotactic polymer was utilized to prepare a unique polymer, hemitactic polypropylene, by hydrogenation of a completely 1,4-trans isotactic poly(2-methyl-1,3-pentadiene). 

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