Study of Radical Polymerization of Arylacetylenes. Composition, Structure, and Some Properties of the Generated Products

Abstract

Abstract Radical polymerization of 2-methyl-5-ethynylpyridine (MEP) and the structure and some properties of phenylacetylene and pentafluorophenylacetylene polymers were investigated. As the first step in polymerization of MEP in the presence of azo-1-cyclohexylcarboxylic acid dinitrile at 94-115°C the monomer conversion is proportional to the quantity of decomposed initiator: 1 mole of initiator causes transformation of 5-7 mole of monomer. At a high degree of polymerization the yield of polymer is not proportional to the initial initiator concentration. The products generated in MEP polymerization initiated thermally or by azo compounds were investigated by means of gel-permeation chromatography, ozonation, 1H-NMR, IR, and UV spectroscopy. Initiation with azo compounds afforded cyclic trimer (tripicolylbenzene) and a fraction with a number average molecular weight Mn of 1550. Thermal polymerization yielded the dimer (picolyl-substituted quinoline or isoquinoline), tripicolylbenzene, hexaraer, and fractions with Mn = 1500 and 1800. Composition and properties of the polymerization products enable one to assume the presence of poly-MEP hexadiene rings in the main chain. Formation of cyclodiene structures by facile aromatization in the course of arylacetylenes polymerization was confirmed by investigations of the structure and some properties of polyphenylacetylenes and polypentafluoro-phenylacetylenes. A mechanism of radical polymerization of arylacetylenes is proposed.