Acetylenes disubstituted, metathesis polymerization

Ziegler-Natta catalysts are not active at all in polymerization of disubstituted acetylenes.415 Mo- and W-based systems (for alkynes with small substituents) and Nb- and Ta-based catalysts (for alkynes with bulky groups), in turn, are very effective catalysts used to convert disubstituted acetylenes into polymers with very high molecular weight.414 415 A polymerization mechanism similar to that of metathesis polymerization of cycloalkenes are supported by most experimental observations.414 423 424... 

Table 10.4 References to the metathesis polymerization of disubstituted acetylenes"... 

Acetylene and mono- and disubstituted acetylenes do not polymerize with conventional free-radical or ionic initiators to high molecular weight polymers in high yields. However, they polymerize via metathesis mechanism in the presence of suitable transition-metal catalysts such as Nb, Ta, Mo, W, or Ru. The polymers possess carbon-carbon alternating double bonds along the main chain and exhibit unique properties such as semimetallic or metallic conductivity, Scheme 15.1. 

Although metathesis catalysts polymerize mono- and disubstituted acetylenes, they do not polymerize monomers having polar and/or protic groups because of their lack of tolerance of these groups. For the same reason, the polymerization with metathesis catalysts is carried out in relatively nonpolar solvents. 

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