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

Abstract

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.

Bithiazole: An Intriguing Electron‐Deficient Building for Plastic Electronic Applications

“…However, no OFET or OPV data was reported for the polymers. The same group later reported a modification to the structure of poly(4‐alkylthiazoles) by synthesizing P60 , P61 , and P62 , which have a silyloxymethyl side‐chain . Once again, it was found that P60 and P62 were relatively insoluble in common organic solvents, however, P61 was fully soluble in hexane.…”

Influence of the halogen and organometallic function in a KCTP (Co)polymerization

“…After the discovery of the controlled nature of the poly(3‐hexylthiophene) (P3HT) polymerization by McCullough and coworkers and Yokozawa and coworkers, the field of conjugated polymers evolved tremendously. While the Kumada Catalyst Transfer Polycondensation (KCTP) mechanism is used to polymerize a wide variety of monomers, the halogen and organometallic function on these monomers are almost consistently bromine and chloromagnesio, respectively . Nevertheless, changing these functions can affect the (co)polymerization of the monomers.…”

Diversifying Cross‐Coupling Strategies, Catalysts and Monomers for the Controlled Synthesis of Conjugated Polymers

“…Both dppp and dppe based catalysts have been used to polymerize a broad range of monomers (Figures and 4). These include phenylenes, thiophenes, pyrroles, furans, selenophenes, tellurophenes, thiazoles, pyridines, fluorenes, thienopyrazines, dithienosiloles, carbazole and rylene diimides . In each of these cases, dramatic differences arise when exploring these different conjugated building blocks.…”

“…Pammer and McNeil have both explored 4‐substituted thiazoles, a related but more electron deficient five‐membered aromatic . Both research teams have noted dramatic changes in solubility for this monomer with the nitrogen atom in the 5‐membered ring, and a large siloxy side chain was necessary to achieve well‐defined polymers with narrow molecular weight distributions.…”