Transition metal catalysts molecular weight control

The thermal ROP of silicon-bridged [l]ferrocenophanes requires moderately high temperatures (100-250°C) and there is little or no molecular weight control. As a result, the molecular weight distributions are quite broad (d/w/47n E5-2.5). This polymerization method has now been superseded in many ways by ambient-temperature ROP methods that involve the use of anionic initiators (see Section 12.06.3.3.4) or transition metal catalysts (see Section 3.3.4). 

We have seen the development of polyethylene, from low molecular weight polymers first mentioned by name in the literature in 1869, to the first reported solid polymers of linear polyethylene by Prof. Marvel in 1930 then the unintentional synthesis and chance observation of 0.4 g of solid polyethylene in March 1933 by ICI (prepared under high pressure, later described as LDPE) the onset of catalyst technology in the industry, from the simultaneous discoveries of transition metal catalysts a few decades later, that created the HOPE industry the development of LLDPE copolymers and the discovery in 1979 of metallocene catalysts for polyolefin polymerization - all of which are now part of the mainstream polyethylene industry. Post-metaUocene catalysts offer the promise of branching without high pressure or comonomers the potential to incorporate polar groups without high pressure, and to control this copolymer microstructure. 

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