Stereoregular Polymerization with Transition Metal Alkyls

V. Stereoregular polymerization with Transition Metal Alkyls. 298... 

Ziegler-Natta catalyst. Gi ulio Natta developed a catalyst based on his work with Karl Ziegler for polymerizing vinyl monomers to give stereoregular, tailored, three-dimensional chains. The catalyst is based on aluminum alkyls and TiCU or other transition metal halides. 

Well-controlled polymerization of substituted acetylenes was also reported. A tetracoordinate organorhodium complex induces the stereospecific living polymerization of phenylacetylene.600 The polymerization proceeds via a 2-1 -insertion mechanism to provide stereoregular poly(phenylacetylene) with m-transoidal backbone structure. Rh complexes were also used in the same process in supercritical C02601 and in the polymerization of terminal alkyl- and arylacetylenes.602 Single-component transition-metal catalysts based on Ni acetylides603 and Pd acet-ylides604 were used in the polymerization of p-diethynylbenzene. 

Before the 1970s, Ziegler-Natta catalysts for a-olefin production were normally prepared from certain compounds of transition metals of Groups IV-VI of the periodic table (Ti, V, Cr, etc.) in combination with an organoraetallic alkyl or aryl (Table I). Practically all subhalides of transition metals have been claimed as catalysts in stereoregular polymerization. Only those elements with a first work function <4 eV and a first ionization potential <7 V yield sufficiently active halides, that is, titanium, vanadium, chromium, and zirconium (7, Only titanium chlorides have gained widespread acceptance in crystalline polyolefin production. 

---