Polymer ditactic

The simplest optically active ditactic polymers prepared so far are isotactic cis and trans 1.4-polypenta-l.3-diene (93, 95). 

It should also be mentioned that atactic polymers may be formed from monodeuteropropylene and pentadeuteropropylene, similarly to the case of the polymerisation of non-deuterated propylene. However, atactic structures with respect to one stereogenic tertiary carbon atom, with the other possibly arranged to form tactic polymer sequences, are not known. Also, ditactic polymers, which might be characterised by the appearance of two distinct series of tacticity as regards both stereogenic tertiary carbon atoms, i.e. the isotactic with respect to one stereogenic carbon atom and syndiotactic with respect to the other one, and vice versa, are not known. 

Show by adopted Fischer projections the various (if any) tactic (ditactic) polymers that might possibly be obtained from each of the olefins ... 

Indicate tactic or ditactic polymers that can be obtained by the coordination polymerisation of oxiranes. 

Tactic polymers are classified as isotactic, syndiotactic, or heterotactic according to how the configurational monomeric units are bonded to each other. If two defined stereoisomeric positions per configurational monomeric unit occur, then this is known as a ditactic polymer, which may, for example, be diisotactic or disyndiotactic. If the configurational monomeric unit has three defined stereoisomeric positions, then the polymer is a tritactic polymer. Polymers of higher tactic number are similarly defined. 

Ditactic polymers possess two stereoisomeric centers per constitutional monomeric unit, and tritactic polymers possess three. Ditactic polymers may be formed by the polymerization of 1,2-disubstituted ethylene derivatives, as, for example, with pentene-2 ... 

Stereospecific ring-opening polymerization of epoxides or episulfides with two asymmetric carbon atoms in the ring. Highly stereoregular ditactic polymers have been obtained from... 

Ditacticity. Ditactic polymers possess two centers of asymmetry per monomeric unit it is the case of 1,2-disubstituted vinyl polymers whose two chiral centers are generated upon polymerization, and it is also the case of heterocycles carrying two centers of asymmetry. The three possible tacticities are schematically represented as follows ... 

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