Construction of hyperbranched poly(alkenephenylene)s by diyne polycyclotrimerization: Single-component catalyst, glycogen-like macromolecular structure, facile thermal curing, and strong thermolysis resistance

A "simple" catalyst of TaBr₅ NbBr₅, or NbBr₃̇CH₃O(CH₂₎₂OCH₃ is developed, which readily effects polycyclotrimerizations of α,ω- alkenediynes {HC≡C(CH_2)mC=CH, m = 4-6 [1(m)]} at room temperature, giving hyperbranched poly(alkenephenylene)s [hb-P1(m)] with high molecular weights (M_w up to ∼270 × 10³) in high yields (normally >80%). The polymers prepared under optimal reaction conditions are completely soluble in common organic solvents such as toluene, THF, and chloroform. Spectroscopic characterizations prove that the polymers comprise of linear (L) and dendritic units (D) of 1,2,4/1,3,5-trialkylbenzenes and terminal unit (T) of 1,2,4-trialkylbenzene (or 6-alkyltetralin). The L and D units are generated by geostructurally different addition modes, similar to those used by nature to create L and D units of glycogen, a hyperbranched biopolymer. With the aids of model reactions and simulations, detailed structural analyses reveal that hb-P1(4) possesses a degree of branching of 64% and consists of 36%, 32%, and 32% of L, D, and T units, respectively, with 1,2,4-trialkylbenzene being the predominant isomeric structure (74%). The polymer shows outstanding thermal properties: it readily cures when baked at a moderate temperature of 100°C and loses little of its weight when heated to a high temperature of ∼500°C.