Synthesis of Poly(vinylene−phosphine)s: Ring-Collapsed Radical Alternating Copolymerization of Methyl-Substituted Cyclooligophosphine with Acetylenic Compounds

A conjugated polymer containing a phosphorus atom in the main chain, poly(vinylene−phosphine), was synthesized by ring-collapsed radical alternating copolymerization (RCRAC) of a cyclooligophosphine and phenylacetylene ( 1a ). Under a nitrogen atmosphere, pentamethylcyclopentaphosphine ( cyclo -(MeP) 5 ) and 1a were reacted in the presence of a catalytic amount of 2,2‘-azobis(isobutyronitrile) (AIBN) at 78 °C in deaerated benzene for 8 h. Poly(vinylene−phosphine) ( 2 ) was obtained as a yellow powder after purification by reprecipitation into n -hexane three times and freeze-dried for 10 h. The number-average molecular weight of polymer 2 was 2500, which is estimated by gel permeation chromatographic (GPC) analysis (chloroform, PSt standards). The structure of 2 was supported by 1 H, 13 C, and 31 P NMR spectroscopies, suggesting that trans isomers of diphosphaalkene units were mainly formed in the main chain. The UV−vis absorption spectrum of polymer 2 in chloroform showed small absorption at a visible region derived from the n−π* transition in the main chain as well as strong absorption at a UV region derived from aromatic groups. The fluorescence spectrum of a dilute chloroform solution of 2 showed an emission peak at 470 nm, which derived from the n −π* transition along the polymer backbone.