Transition metal initiator

Block copolymers have been successfully synthesized because many metallocene polymerizations of MMA proceed as living polymerizations, and it is possible to have a single one-way crossover from carbanion (alkene) polymerization to MMA (enolate) polymerization with metallocene and related initiators, especially when group 3 transition metal initiators are used [Boffa and Novak, 2000 Desurmont et al., 2000a,b Jin and Chen, 2002 Yasuda et al., 1992],... 

The transition metal initialized dehydrogenation of hydridocarbosilanes to yield further crosslinked organosilicon polymers can be monitored by IR- and H NMR spectroscopic methods Decreasing of the intensity of both the Si-H stretching vibration as well as of the Si-H resonance signal is observed. 

TABLE 2.17 Microstructure of Polydienes from Transition Metal-Initiated Polymerization ... 

One suggested mode of polymerization with metal oxide catalysts envisages reaction in a chemisorbed monomer layer. In this mechanism, ethylene is chemisorbed on the catalyst surface by interaction of the monomer ir-electrons and unpaired electrons of the transition metal. Initiation involves the supply of an unpaired electron from a metal atom to an adjacent adsorbed monomer molecule propagation then ensues by reaction of the product with a neighbouring adsorbed monomer molecule. The process may be depicted as follows ... 

Besides transforming the N-terminus of the polypeptide chain after the NCA polymerization, bifunctional initiators can be employed (see Table 2). The method can be carried out with amine-initiated NCA polymerization [80] or transition metal-initiated NCA polymerization [79]. In the latter case, it has been shown that the ATRP group is stable in the presence of the nickel catalyst used for the NCA polymerization [79], although nickel complexes can also be used as catalysts in the ATRP polymerization [99]. 

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