Cyclopolymerization of α-methylbenzyl dipropargylamine by transition metal catalysts

Abstract

π-Conjugated oligomers and polymers are intensively studied mainly because of their interesting electrical and optical properties and, more importantly, their potential utility in electronics and photonic applications. Among the π-conjugated polymers, the polyacetylene (PA) is structurally the simplest one, and it can be made freestanding thin film by using Shirakawa catalysts [Ti(OC4H9)4Al(C2H5)3]. 6 However, the drawbacks are that PA is insoluble, infusible, and unstable to air oxidation. Thus it was difficult for practrical applications to opto-electronic devices as an active material. To overcome these problems of PA itself, more stable heterocycle-based polymers such as polypyrrole and polythiophene were prepared, and these materials can be easily obtained in their oxidized conducting form by means of one-step electrochemical synthesis. And also, a number of substituted PAs has been prepared by the simple linear polymerization of the corresponding acetylene monomers by various catalyst systems. The polymers having a conjugated backbone are expected to show unique properties such as electrical conductivity, paramagnetism, migration and transfer of energy, color, and chemical reactivity and complex formation ability. Because of these properties, polyacetylene and its homologues have been promising as organic semiconductors, as membranes for gas separation and for liquid-mixture separation, as chiro-optical materials, as side-chain liquid crystals, and as materials for nonlinear optical property and for photoluminescence and electroluminescence properties. Cyclopolymerization of nonconjugated diynes is very interesting method for the synthesis of conjugated polymer system via an alternating intramolecular-intermolecular chain propagation. 1,6-Heptadiyne itself has been polymerized by various transition metal catalysts into a polyene of cyclic structure. The resulting poly(1,6-heptadiyne)s obtained were dark red or black, which indicates a high order of conjugation in the polymer. However, the poly(1,6-heptadiyne)s were also insoluble in any organic solvent and unstable to air oxidation as like with that of PA. Introduction of substituents at 4-position of 1,6-heptadiyne can help enhance the processibility and stability of the polyene systems, thus a variety of substituted poly(1,6-heptadiyne)s were designed and synthesized. In recent years, nitrogen-containing polymers have received unabated attention in the design and synthesis of multifunctional polymers. Unlike other π-conjugated polymers, they contain nitrogen heteroatom either in the main chains or in the side chains that provide facile quaternarization reaction and protonation of the nitrogen sites. Now, we report the synthesis of new conjugated cyclopolymer by the cyclopolymerization of a dipropargylamine derivative and the characterization of the resulting conjugated polymer.