Molecular Oxygen Insertion Polymerization into Crystals of Tetrakis(alkoxycarbonyl)quinodimethanes

Solid-state alternating copolymerization took place by molecular oxygen insertion in the crystals of 7,7,8,8-tetrakis(ethoxycarbonyl)quinodimethane (1a) and 7,7-bis(ethoxycarbonyl)-8,8-bis(methoxycarbonyl)quinodimethane (1b) to form highly crystalline needlelike white solids for 1a and amorphous ones for 1b. The polymer structures were confirmed by 1H NMR, 13C NMR, IR, elemental analysis, powder XRD, and TGA measurements. However, in vacuo polymerizations of 1a and 1b in the solid state with heating and photoirradiation did not take place. 7,7,8,8-Tetrakis(methoxycarbonyl)quinodimethane (1c) did not undergo solid-state alternating copolymerization with oxygen even in the presence of oxygen, but instead it homopolymerized to form highly crystalline homopolymer. The difference in the solid-state polymerization reactivity was discussed on the basis of molecular packing in the crystals obtained by X-ray crystallography. In addition, it was found by ESR measurement that the solid-state alternating copolymerizations with molecular oxygen proceed by means of a radical mechanism.