Ring-Collapsed Radical Alternating Copolymerization of Phenyl-Substituted Cyclooligostibine and Acetylenic Compounds

We studied ring-collapsed radical alternating copolymerization (RCRAC) of hexaphenylcyclohexastibine ( cyclo -(PhSb) 6 ) and several acetylenic compounds in the presence of a catalytic amount of 2,2‘-azobis(isobutyronitrile) (AIBN) in tetrahydrofuran at 70 °C. Although the monosubstituted acetylenic monomers, phenylacetylene ( 1a ), 4-cyanophenylacetylene ( 1b ), and 4-methoxyphenylacetylene ( 1c ), gave low molecular weight poly(vinylene stibine)s, RCRAC of dimethyl acetylenedicarboxylate ( 1d ) and cyclo -(PhSb) 6 provided a corresponding poly(vinylene stibine) ( 2d ) of which the number-average molecular weight was 4300 by gel permeation chromatographic analysis. The structure of 2d was supported by 1 H and 13 C NMR spectra and elemental analysis. The structure and the molecular weight of 2d were insensitive to solvents and the feed ratio of the monomers. When hexaphenylcyclohexaarsine ( cyclo -(PhAs) 6 ) was used in RCRAC with 1d, no polymerization proceeded. These results were derived from different reactivity of pnictogen radicals. When the results of RCRAC of cyclo -(PhAs) 6 and that of 2 are compared, the arsenic radicals had more reactivity to the ethynyl groups and the antimony radicals had more reactivity toward the vinyl radicals.