The performance of catalyst transfer polymerization (CTP) reactions which depend on catalyst association was studied on 3,6-dioctylthiothieno[3,2-b]thiophene (TT)-monomers. This monomer was selected because a strong association of the catalyst is expected, since the aromaticity of thienothiophene is largely maintained when the catalyst and thienothiophene associate. This study includes both reported and unreported Ni- and Pd-catalyst systems. It is found that no polymer formation can be observed using Ni-catalysts, whereas Pd-catalysts show a similar behavior as for other monomer systems. During the study of the Ni-catalyzed CTPs, the p-associated Ni-0-complex has been isolated in situ and displayed a high stability in solution. It is shown that the associated complex interferes with the polymerization reaction and even prevents polymer formation. Furthermore, this complex prevented any Kumada-coupling reaction in the presence of the TT unit, as it serves as a trapping site for free Ni-0-catalyst entities. Ni-0-trapping does not occur during polymerization of 3-alkylthiophene, confirming the presence of the pi-associated Ni-0-complex in this polymerization. This introduces a new convenient method of probing Ni-0-association during all Ni-catalyzed reactions. Furthermore, these results establish the presence of an upper limit to the catalyst association strengthabove which oxidative addition is prevented and the polymerization is inhibitedand they therefore add extra considerations for optimal catalyst design.