Investigation of Bimetallic Nickel Catalysts in Catalyst-Transfer Polymerization of π-Conjugated Polymers

A comparative study involving bimetallic nickel catalysts designed from disubstituted N,N,N ',N '-tetra(diphenylphosphanylmethyl)benzene diamine bridging ligands is reported. Catalyst behavior is explored in the Kumada catalyst-transfer polymerization (KCTP) using poly(3-hexylthiophene) (P3HT) as the model system. The success of a controlled polymerization is monitored by analyzing monomer conversion, degree of polymerization, end-group identity, and molecular weight distribution. The characterization of P3HT obtained from KCTP initiated with the bimetallic catalysts shows chain-growth behavior; however, the presence of Br/Br end-groups and broader molecular weight distribution reveals a reduced controlled polymerization compared to the commonly employed Ni(dppp)Cl-2. The observed increase in intermolecular chain transfer and termination processes in KCTP initiation with the bimetallic catalysts can be attributed to a weaker Ni(0)-pi-aryl complex interaction, which is caused by increased steric crowding of the coordination sphere.