Carbocationic polymerization in the gas phase: polymerization of acetylene induced by BF2+

Gas-phase measurements for the primary reaction of BF2+ with acetylene and the ensuing higher-order reactions with acetylene have been performed at 296 ± 2 K in helium at 0.35 torr using the Selected-Ion Flow Tube (SIFT) technique. The primary reaction was observed to be rapid and to produce two species which both initiated rapid polymerization of acetylene. The major primary product, C2HBF+, was observed to initiate the sequential addition of four molecules of acetylene, most likely by termolecular association reactions. The first few steps in this polymerization were also followed using abinitio molecular orbital theory. The calculations and measurements provide structural, energetic, and kinetic information and, in combination, reveal several intrinsic features of the initial steps of the cationic polymerization of acetylene initiated by BF2+. Keywords: polymerization, acetylene, aromaticity.