Soluble Head-to-Tail Regioregular Polythiazoles: Preparation, Properties, and Evidence for Chain-Growth Behavior in the Synthesis via Kumada-Coupling Polycondensation

Head-to-tail regioregular poly­(4-alkylthiazole)­s containing silylethers in the side-chains were synthesized via Kumada-Coupling polycondensation of “reversed” monomers, that were metalated at the sterically hindered 5-position. Their optical, electrochemical, and bulk properties have been studied, and evidence is presented that indicates the occurrence of quasi-living chain-growth behavior in the polymerization process. Two polymers, PTzTIP and PTzDIBO, featuring triisopropylsilyl and diisobutyloctadecylsilyl side chains, respectively, were prepared. PTzTIP is largely insoluble, while PTzDIBO is fully soluble in common organic solvents, including hexane, and readily gave number-averaged molecular weights exceeding 100 kDa, corresponding to an average degree of polymerization greater than 200, as determined via gel-permeation chromatography (GPC) in CHCl₃. The formation of a regular head-to-tail regiostructure could be confirmed through comparison with a head-to-head–tail-to-tail regioregular polybithiazole (PBTzTIP), synthesized via Yamamoto-polymerization of a head-to-head-linked bithiazole. Regioregular PTzDIBO could be obtained via different polymerization protocols, including external initiation with two new aryl-nickel-complexes, which furnished material with particularly low polydispersities (<1.4 at M_n > 100 kDa). Furthermore, a direct correlation between the obtained molecular weight and the monomer/catalyst ratio was observed in series of batch polymerization experiments, in agreement with a chain-growth polycondensation process. The incorporation of the precatalyst–aryl moiety into the polymer chains could be proven by comparison with a model compound. The functionalized end-groups allowed to independently determine the molecular weight via ¹H NMR, which gave good agreement with the values obtained from GPC, further corroborating the occurrence of chain-growth.