Regiospecific polymerization

The polymer composed of 2-cyclohexenyl-l,4 units can exhibit high Tg (176 °C) when the tacticity is controlled well [62]. Recently, [( -allyl)NiBr]2, in conjunction with MAO, was found to initiate stereo- and regiospecific polymerization of 1,3-cyclohexadiene [63]. Although the polymer has too poor solubility in organic solvents to be analyzed by NMR spectroscopy, the copolymers of 1,3-cyclohexadiene with 1,3-butadiene and norbornene prepared by the Ni catalyst show NMR spectra that indicate the presence of the 2-cyclohexene- 1,4-diyl unit formed via 1,4-polymerization of 1,3-cyclohexadiene (Eq. 11). X-ray diffraction analysis of the crystalline poly( 1,3-cyclohexadiene) as well as studies by molecular dynamics confirmed the cis-syndiotactic structure of the polymer [64]. 

A third, non-catalytic approach to regioregular polythiophenes relies on the discovery by Andersson and co-workers that the oxidation of some monomers can be controlled giving high coupling selectivities. For example, phenyl-substituted thiophene monomers can be regiospecifically polymerized by a slow addition of FeCH that maintains a low concentration of radical throughout the reaction. Yields approaching 80 %... 

Nakano, M. Yao, Q. Usuki, A. Tanimura, S. Matsuoka, T. Stereo- and regiospecific polymerization of cyclic conjugated dienes using highly active nickel catalysts. Chem. Commun. 2000, 2207-2208... 

Early studies showed that polymers possessing some regiospecificity exhibit improved electrical and magnetic properties when compared to random polythiophenes [234]. In this instance, P3ATs 56 were synthesized by polymerization of 3,3 -dialkyl-2,2 -bithiophene 55 as shown in Scheme 55. Polymerization either electrochemically or via Lewis acid yielded predominantly HH-coupled polymers whose absorption maxima blue shifted -90 nm for 3,3,-dimethyl-2,2 -... 

K. Kobayashi and T. Kondo, Synthesis of a regiospecifically fluorinated polysaccharide 3-deoxy-3-fluoro-(l — 6)-o -D-glucopyranan via ring-opening polymerization, Macromolecules, 30 (1997) 6531-6535. 

Fig. 10 Topological classification of linear polymeric polyradicals, including a scheme showing the importance of regiospecific connectivity.

A new approach to 1,2,4-thiadiphospholes 129 via a regiospecific reaction of phosphaalkynes 128 with sulfur in the presence of the polymeric thiotantalum(v) sulfide [STaC ] was reported by Regitz and co-workers (Equation 12) <2002EJ01664>. 

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