Synthetic polymers stereochemical control

An example of such modeling of a stereochemically variable polysiloxane focused on poly[methyl(3,3,3-trifluoropropyl)siloxane],137 a polymer much studied with regard to the already-mentioned new synthetic techniques for controlling stereoregularity and thus crystallizability.102-104 138... 

The synthetic application of the direct coupling of two acetylene units was initially limited by the formation of mixtures of regio (head-to-head and head-to-tail) and stereo (E/Z) isomers, and preference for trimerization processes [4], During recent years, however, increased regio and stereochemical control has been achieved by the appropriate choice of catalyst. For example, conjugated polymers with enriched ( ), (Z), or gem-vinylene linkages are selectively obtained by the use of suitable Pd, Ru, or Rh catalysts, respectively [5]. 

Atomic Structure. The control of atomic structure is fundamental to any system, and an incomplete understanding of atomic structure can limit advancement. For example, our understanding of preceramic polymers, up through the formation of networks, is improving but the full exploitation of this chemistry is still limited by the lack of detailed knowledge of the structure of the resulting ceramic at the atomic level. Even with more familiar silicone polymer systems, synthetic barriers are encountered as polymers other than poly(dimethylsiloxane) are used. Stereochemical control is inadequate in the polymerization of unsymmetrical cyclic siloxanes to yield novel linear materials. Reliable synthetic routes to model ladder systems are insufficient. 

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