Rhodium-Catalyzed Polycyclotrimerization of Diphenylpropiolates: A Facile Strategy toward Ester-Functionalized Hyperbranched Polyarylenes

Alkyne polycyclotrimerizations have become efficient synthetic tools for constructing hyperbranched polyphenylenes. However, the polycyclotrimerization reactions of internal alkynes are rarely reported. Herein, we present the first example of RhCl3-catalyzed polycyclotrimerization of activated internal diynes to prepare hyperbranched polymers. The polymerization reactions of diphenylpropiolates (1a–c) were performed in toluene under reflux in the presence of RhCl3·3H2O and N,N-diisopropylethylamine (DIPEA), affording soluble hyperbranched poly­(triphenylbenzoate)­s (hb-PTPBs), hb-P1a–c, with high molecular weights (up to 187000) and high regioregularities (fraction of 1,2,4-triphenylbenzoate isomer up to 88.2%) in satisfactory yields. The degree of branching of hb-P1a was determined to be 0.73. The resultant hb-PTPBs are thermally stable, with 5% weight loss temperatures higher than 330 °C. The hb-PTPBs are weakly emissive in their dilute solutions but become intensively emissive upon aggregate formation, showing aggregation-induced emission features.