Silicon Promoted Cationic Polymerization of Phenylacetylenes

Poly(phenylacetylene)s (PPAs) are widely applied in a variety of research fields due to their good electrical and optical properties. Transition-metal-catalyzed polymerizations are generally performed for the synthesis of PPAs, while the residual metal catalysts might be problematic. In this work, we present a silicon promoted cationic polymerization of phenylacetylenes (PAs) by introducing a labile and electron-donating silyl group at the alkynyl termini of PA monomers. The polymerizations were performed in the presence of trifluoromethanesulfonic acid to rapidly produce the PPA products with good yields. The structures of the PPAs were characterized by NMR, IR, MALDI-TOF MS, UV–vis, and fluorescence spectroscopies, showing that the PPAs consist of conjugated skeletons with high contents of trans-configurations. GPC analysis showed a relatively narrow molecular weight distribution, and the molecular weight reached up to 4.7 kDa. A possible reaction scheme was proposed through further analysis on the structures of three kinds of oligomeric species. As the silyl groups are generally inherited from Sonogashira coupling reactions during the synthesis of PAs, this work presents a straightforward and metal-free method for the synthesis of PPAs.