Effects of ortho-substituents on the living polymerization of phenylacetylenes by MoOCl4-based catalysts

Polymerization of phenylacetylenes (PAs) having various ortho‐substituents were examined by using MoOCl4—n‐Bu4Sn—EtOH (mole ratio 1:1:1) as catalyst. Phenylacetylenes with no or sterically small ortho‐substituents did not polymerize in a living fashion. On the other hand, in the polymerization of phenylacetylenes having medium‐sized substituents (e.g., CH3, Cl, Br, and iPr), the number‐average molecular weights Mn of polymers increased in direct proportion to monomer consumption, while the polydispersity ratios were 1,2– 1,3, which is in favor of living polymerization. Further, monomers having bulky ortho‐groups (CF3 and Me3Ge) exhibited excellent living nature with small polydispersity ratios of ≈ 1,1. Thus, it is concluded that not the electronic but the steric effect of the ortho‐substituent is important to achieve living polymerization.