Butynes living polymerization

A Ta vinylalkylidene complex 6, confirmed by a single crystal X-ray analysis, was revealed to polymerize 2-butyne in a manner of living polymerization.The initiation efficiency is quantitative, and the living end can be end-capped with aromatic aldehydes. As polymers from symmetric acetylenes are generally insoluble, soluble poly(2-butyne) is accessible if the degree of polymerization is suppressed below 200. The NMR analysis of living oligomers of 2-butyne clearly indicates that both cis- and 7ra r-structures exist in the main chain. 

It was reported that the alkylidene mechanism for the living polymerization of 2-butyne and acetylene itselP was operative in two systems that contained well-defined alkylidene complexes, although controlled living acetylene polymerization by well-defined initiators is still relatively rare. 

A Ta carbene complex (2 in Table 15.2) is the first example of a single-component metathesis catalyst that induces the living polymerization of substituted acetylene, where the monomer used is 2-butyne [37]. The initiation efficiency is quantitative. 

---