New soluble unsaturated polyketone derived from diarylidenecycloalketone: synthesis and optical and electrochemical properties of π-conjugated poly(diarylidenecyclohexanone) with long side chains

A new type of unsaturated polyketone having cyclohexanone moiety in a π-conjugated main chain was prepared by polycondensation between 2,6-bis(4-bromobenzylidene)cyclohexanone and 2,5-dihexyloxy-p-phenylene diboric ester in the presence of Pd(PPh₃)₄. The polymer had good solubility in common organic solvents. Analysis by gel permeation chromatography (GPC; polystyrene standards) showed that the polymer had M_n and M_w values of 7800 and 18?200, respectively. The polymer exhibited a η] value of 0.70 dl g⁻¹ in benzene at 30 °C. The chloroform solution of the polymer showed an UV-Vis peak at 392 nm, and the PL spectrum gave a peak at 533 nm. DSC exhibited that the polymer had a T_g of 85 °C. The DSC data, observation with a polarizing microscope, X-ray diffraction data and UV-Vis data of the obtained polymer showed a phase transition above 200 °C. TGA showed that the polymer had good thermal stability with 5 wt% loss temperature of 407 °C under N₂. Electrochemical oxidation (or p-doping) of the polymer started at about 0.7 V vs. Ag/AgNO₃ and gave a peak at 1.06 V vs. Ag/AgNO₃ with a color change of the film from yellow to deep red. The color change was followed by UV-Vis spectroscopy. The corresponding p-dedoping peak appeared at 0.58 V vs. Ag/AgNO₃.