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Syntheses, characterizations, and properties of regiospecific poly(3-alkylthiophenes), poly(phenylcarbyne), and related polymers mediated by Rieke metals
Abstract
Highly reactive metals (Rieke metals) were found to be a very useful tool in the synthesis and modification of special polymers and new materials. Rieke zinc reacted, chemoselectively, with dihaloarylenes, such as 2,5-dibromothiophene, para-diiodobenzene, and their substituted derivatives, to afford the quantitative mono-organozinc arylenes, which were polymerized upon treatment with a catalytic amount of Pd($\rm PPh\sb3)\sb4$(0.2 mol-%) to yield the conjugated polyarylenes, such as polythiophene and poly(para-phenylene), quantitatively. This novel methodology had been expanded to a systematic regiocontrolled synthesis of poly(3-alkylthiophenes). Rieke zinc underwent oxidative addition to 2,5-dibromo3-alkylthiophenes or 2-bromo-5-iodo-3-alkylthiophenes regioselectively to afford the 2-bromo-5-(bromozincio)-3-alkylthiophene or 2-bromo-5-(iodozincio)-3-alkylthiophene. The same monoorganozinc 3-alkylthiophene intermediate can be polymerized catalytically to a series of poly(3-alkylthiophenes) (P3AT) with the degree of regioregularity in the polymer chain dependent on the specific catalyst employed. The regioregularity of the polymer chain was solely controlled by the structure of the catalyst. An almost completely regioregular head-to-tail (HT $>$ 98.5%) P3AT catalyzed by Ni(DPPE)Cl$\sb2$ and a totally regiorandom (50:50, head-to-tail:head-to-head) P3AT catalyzed by $\rm Pd(PPh\sb3)\sb4$ were most significant. The regioregular HT P3ATs were consistently characterized as a class of low bandgap and highly electroconductive polymers with regiospecific head-to-tail conformation, significantly extended conjugation length, self-organized chain structure, and polycrystalline texture by NMR, FTIR, electronic absorption, X-ray diffraction, electron spin resonance, cross-polarized microscopy, and electroconductivity studies. The neutral and doped regioregular HT P3ATs had three orders of magnitude higher conductivities than that of the regiorandom P3ATs. The temperature dependence of conductivity and magnetoresistivity showed that regioregular HT P3ATs were near the critical regime of disorder-induced metal-insulator transition (MIT), while regiorandom P3ATs were in the insulating regime. A light-violet electroluminescence was produced by a blend of HT-P3HT and poly(9-vinylcarbazole) (blend ratio = 1/60 by weight). The electroluminescence quantum efficiency was enhanced by blending, i.e., greater than in pure PVK (poly(9-vinylcarbazole)) by approximately a factor of 4 and greater than in pure HT-P3HT by more than two orders of magnitude. A facile synthesis of poly(phenylcarbyne), a novel polymer precursor to diamond or diamond-like carbon, was developed using Rieke metals, such as Rieke calcium, strontium, and barium. The reaction of 1.0 equivalent of $\alpha ,\alpha , \alpha$-trichlorotoluene with 1.5 equivalent Rieke metal gives poly(phenylcarbyne) with 46% yield which is almost double that of the traditional method.
Subject Area
Polymers|Organic chemistry|Materials science
Recommended Citation
Chen, Tian-An, "Syntheses, characterizations, and properties of regiospecific poly(3-alkylthiophenes), poly(phenylcarbyne), and related polymers mediated by Rieke metals" (1994). ETD collection for University of Nebraska-Lincoln. AAI9510965.
https://digitalcommons.unl.edu/dissertations/AAI9510965