Metal-free polycyclotrimerization of trimethylsilyl-protected diynes: a facile strategy toward regioregular hyperbranched polyarylenes

Exploration of efficient polymerization strategies is critical in polymer science. Alkyne polycyclotrimerization reactions have become powerful synthetic tools for constructing hyperbranched polyarylenes ( hb -PAs). However, most of the polymerization reactions suffer from the requirement of using transition metal catalysts, and yield mixtures of 1,2,4- and 1,3,5-trisubstituted benzene isomers in their products. In this work, we provide the first example of metal-free polycyclotrimerization of internal diynes to synthesize regioregular hb -PAs. The polymerizations of trimethylsilyl-protected aromatic diynes ( 1a-e ) proceeded smoothly in the presence of p -toluenesulfonic acid monohydrate, producing soluble hb -PAs, hb -P 1a-e , with high molecular weights ( M w up to 32 200) and perfect 1,3,5-regioregularity in satisfactory yields. The degree of branching of hb -P 1e was calculated to be 0.68. The polymerization reaction was insensitive to moisture and oxygen. The hb -PAs exhibited high thermal stabilities with 5% weight loss at temperatures up to 391 °C and electrochemical activities. Moreover, the hb -PAs containing tetraphenylethene moieties are weakly emissive in solution but highly fluorescent in the aggregated state, displaying aggregation-induced emission properties. A metal-free p -TsOH·H 2 O-catalyzed polycyclotrimerization of internal alkynes is developed to produce hyperbranched polyarylenes with electrochemical activities and aggregation-induced emission characteristics.