Investigation on radical polymerization behavior of 4-substituted aromaticenynes. Experimental, ESR, and computational studies

The radical polymerization of 4-substituted aromatic enynes was carried out to obtain polymers containing acetylene moieties in the side chain. The po lymers prepared at 60 degreesC consisted of 1,2-polymerized units (i.e., un its having pendent acetylene moieties) regardless of the character of the s ubstituents. The Q and e values of enyne monomers were estimated from copol ymerization with methyl methacrylate. The large Q values (Q = 4.1-5.5) indi cate that the propagating radicals are highly stabilized by the arylethynyl groups which is supported by both the ESR experiments and molecular orbita l calculations. The e values (e = -0.1 to -0.6) were in good agreement with the Hammett sigma (p) values of the substituents on the benzene rings.