Polymers cistactic

A common feature of catalysts based on 4 and 5f block elements is that of being able to polymerize both butadiene and isoprene to highly cistactic polymers, independently of the ligands involved. Butadiene, in particular, can reach a cistacticity as high as 99% with uranium based catalysts (3) and cistacticity of > 98% with neodymium based catalysts (4). This high tacticity does not change with the ligand nature (Fig. 1) in contrast to conventional catalysts based on 3-d block elements. A second feature of f-block catalysts is that the cis content of polymer is scarcely... 

A cistactic polymer is a tactic polymer in which the main chain double bonds of the configurational base units are entirely in the cis arrangement. A transtactic polymer is a tactic polymer in which the main chain double bonds of the configurational base units are entirely in the trans arrangement [134]. Geometrical cis-trans isomerism also arises from different configurations of substituents on a cyclic structure. 

Note 1 Terms referring to the tacticity of polymers (tactic, ditactic, tritactic, isotactic, cistactic, etc.) can also be applied with similar significance to chains, sequences, blocks, etc. 

When all of the double bonds in the polymer molecule have the same configuration, the result is two different ordered polymer structures—transtactic and cistactic. Figure 8-5 shows the structures of the completely cis and completely trans polymers of isoprene. The stereochemistry of these polymers is indicated in their names. For example, the trans polymer (IX) is named as trans-1,4-polyisoprene or poly( -l-methylbut-l-ene-l,4-diyl). The first name is the IUPAC-recommended trivial name the second name is the IUPAC structure-based (Sec. l-2c) [IUPAC, 1966, 1981, 1996],... 

---