ABSTRACT
Acetylene and its mono-and disubstituted derivatives polymerize in the presence of suitable catalysts to provide linear polymers (Scheme 21.1).1-6 Their polymerization behavior greatly varies, depending on the number and kind of substituents on the monomer. Unlike vinyl polymers, the formed polyacetylenes possess carbon-carbon alternating double bonds along the main chain, and hence they belong to the group of conjugated polymers. The alternating double bond structure endows these polymers with unique properties such as electrical conductivity, paramagnetism, color, photoconductivity, electroluminescence, and electrochromism.7-10 Although various catalysts, including radical and ionic initiators and metal complexes, have been examined for the polymerization of acetylenes, only a restricted number of transition metal catalysts are able to selectively polymerize them. Polymerization of acetylenes is often accompanied by cyclotrimerization and linear oligomerization; hence, judicious choice of catalysts is essential. Furthermore, the type of monomers polymerizable with a particular catalyst is typically rather restricted, and therefore it is important to recognize the characteristics of each catalyst. Figure 21.1 shows typical catalysts used for the polymerization of
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HC CR CH C
R
CC
R′R
HC CH CH CH
n
n
n
R, R′ = alkyl, aryl, halide, etc.
