Soluble Polymer Precursors via Ring-Expansion Metathesis Polymerization for the Synthesis of Cyclic Polyacetylene

Abstract

Cyclic polyacetylene (c-PA) is the cyclic derivative of the semiconducting linear polyacetylene. As with the linear derivative, cyclic polyacetylene is insoluble, making its characterization and processing challenging. Herein, we report the synthesis of c-PA via an indirect approach, employing ring-expansion metathesis polymerization of cyclic alkenes to form soluble polymer precursors. Subsequent retro-Diels–Alder elimination through heating provides c-PA. Dilute solution characterizations of the polymer precursors including 1H nuclear magnetic resonance spectroscopy, gel permeation chromatography, and infrared and Raman spectroscopy confirm their cyclic structure and, by inference, the cyclic topology of the resulting c-PA. Solid-state thermal analyses via thermogravimetric analysis and differential scanning calorimetry reveal the chemical and physical transformations occurring during the retro-Diels–Alder elimination step and concurrent isomerization. Freestanding films are attainable via the soluble precursors, and when doped with I2, the films are semiconducting.