Hyperbranched poly(p-phenylene ethynylene)s

Hyperbranched poly(p-phenylene ethynylenes) (HB-PPEs) were synthesized in an A(2)+ B-3 one-pot approach by the Pd/Cu-catalyzed cross-coupling reaction of 1,4-diethynyl-2,5-bis-(octyloxy)benzene and 1,2,4-tribromobenzene. Reaction conditions were varied with the objective to obtain well-defined HB-PPEs of different molecular weights. HB-PPEs with (M) over bar (W) from 11000 to 237 000 g.mol(-1) and PDIs of 1.5-10.7 were prepared. All polymers that comprised unreacted ethynyl groups eventually became insoluble upon drying, presumably as a result of solid-state cross-linking. This reaction could be prevented by endcapping the polymers with an excess of 4-iodotoluene.