Toward Perfect Control of End Groups and Polydispersity in Poly(3-hexylthiophene) via Catalyst Transfer Polymerization

2011-05-10T00:00:00Z (GMT) by Ruth H. Lohwasser Mukundan Thelakkat
We report the influence of the active Grignard monomer formation on the end groups and polydispersity of poly(3-hexylthiophene) (P3HT) for the catalyst transfer polymerization. The rate of the active Grignard monomer formation of 2,5-dibromo-3-hexylthiophene using <i>t</i>-BuMgCl was studied using <sup>1</sup>H NMR. Only in the absence of unreacted/excess <i>t</i>-BuMgCl, polymers with 100% H/Br end groups were formed. If the active Grignard monomer formation was incomplete and thus unreacted <i>t</i>-BuMgCl remained, the end groups depended on the polymerization time; the ratio of H/Br to H/H end groups decreased with increasing time. LiCl was shown to accelerate the active Grignard monomer formation but negatively affects the regioregularity to a small extent. It also increases the molecular weight of P3HT when used in combination with Ni(dppp)Cl<sub>2</sub> as a catalyst. Further, MeOH as a quenching reagent was identified to cause chain−chain coupling and hence an increase in the polydispersity. Thus, important parameters influencing the kinetics of the catalyst transfer polymerization were studied, and a series of P3HTs with 100% H/Br end groups and low polydispersities were synthesized by an optimized procedure. These findings are very relevant for extending this polymerization method to new monomers and for the realization of well-defined block copolymers.