Head-to-Tail Regioregular Polythiazole Prepared via Kumada-Coupling Polycondensation

Abstract

Head-to-tail regioregular poly(4-alkylthiazoles) (C 9 -pTz, C 13 -pTz, alkyl = n-C9H19, n-C13H27) have been synthesized and spectroscopically and electrochemically characterized. The PTzs were obtained by transmetalation of 2-chloro-5-bromo-4-alkylthiazoles with i PrMgCl, followed by Kumada-coupling polycondensation. The polymers are largely insoluble in organic solvents but dissolve readily in the presence of, e.g., trifluoro acetic acid (TFA). Analyses of soluble trace fractions of the polymers gave number average molecular weights (M n) of 1.9–2.4 kDa (C 9 -pTz, PDI ≈ 1.1–1.3) and 2.9–3.0 kDa (C 13 -pTz, PDI ≈ 1.1–1.2), as determined by gel permeation chromatography (GPC) relative to polystyrene standards, while the molecular weight of the bulk material is presumed to be considerably higher. Comparison of the 1H NMR spectra of the PTzs with a quaterthiazole model compound (4Tz) and head-to-head–tail-to-tail regioregular polybithiazole (PBTz) confirmed the head–tail structure and the high degree of regioregularity. The optical and electrochemical band gaps of C 9 -PTz were found to be similar to those of poly(3-hexylthiophene) (P3HT), while the frontier orbital levels are stabilized by 0.3–0.5 eV relative to those of the polythiophene. The synthesis of PTz via selective transmetalation of the precursor at the sterically hindered 5-position renders this synthesis a rare polycondensation of a reversed monomer. The implications for the polymerization mechanism are also discussed.

Synthesis, Properties, and Solar Cell Performance of Poly(4‐(p‐alkoxystyryl)thiazole)s

“…Comparison of cyclic voltammograms of PvTzHD with P3HT and C 13 ‐PTz. Data for P3HT and C 13 ‐PTz, adapted from reference *: internal reference ferrocene.…”

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.…”

Application of named reactions in polymer synthesis

“…To further expand the scope of controlled polycondensation towards other electron-deficient building blocks, Pammer et al [29] recently presented the synthesis of head-to-tail regioregular poly(4-alkylthiazole) compounds via Kumadacoupling polycondensation of 2,5-dihalogenated-4-alkylthiazoles (Scheme 1). Subsequent analysis showed that the number average molecular weights (M n ) of poly(4-nonylthiazole) (C 9 -PTz) were 1.9-2.4 kDa with a Polydispersity Index (PDI) of about 1.1-1.3 and the M n of poly(4-tridecylthiazole) (C 13 -PTz) were 2.9-3.0 kDa (PDI1.1-1.2).…”

“…In comparison with the AB approach, the AA/BB approach of SPC is more popular, most likely because the monomers are easier to synthesize. For example, a high molecular weight copolymer comprised of alternating Scheme 1 Synthesis of C 9 -PTz and C 13 -PTz via Kumada polymerization [29]. benzothiadiazole (BTZ) and cyclopentadithiophene (CDT) units was synthesized by Müllen et al (M n =50 kDa, Scheme 2) [33].…”