Polymerization of m-Diethynylbenzene and Electrical Properties of the Polymer

Abstract

Oxidative coupling polymerization of m-diethynylbenzene (MEB) was carried out in the presence of the copper(I) chlorideN, N, N', N'-tetramethylethylenediaminepyridine system in o-dichlorobenzene, nitrobenzene, diphenyl ether, quinoline, N, N-dimethylformamide, and dimethyl sulfoxide at 90°C (Table 1). The polymer obtained could be manufactured into a tough film by the solvent casting method when its solution viscosity in nitrobenzene at 160°C was more than 0.19η_sp/C. Copolymerization of MEB and p-diethynylbenzene (PEB) was carried out in o-dichlorobenzene and nitrobenzene at 95°C (Table 2). The copolymerization with monomer feed of 7.4 to 10 mol% of PEB proceeded without depositing a polymeric product to yield the copolymer with higher molecular weight in comparison with that of the homopolymer of MEB.
Thormal degrad ation behavior of the homopolymer of MEB and copolymer of MEB with PEB was examined by means of thermogravimetry and differential thermal analysis under air and nitrogen atmospheres. Both polymers exhibited a similar thermal stability and the copolymer was slightly more stable than the homopolymer (Figs.1 and 2).
Electrical properties of the homopolymer of MEB doped with v arious electron-accepting dopants such as tetracyanoquinodimethan (TCNQ) (Fig.3), bromine (Fig.4), iodine (Fig.4), and arsenic pentafluoride (AsF₅) (Fig.5) were studied. Conductivity of the undoped homopolymer of MEB was found to be 9.5×10-^-18 s/cm. It was found that conductivity of the doped polymers increased with the amount of the dopant and reached to 2.9×10^-9 and 2.81×10^-11 s/cm when TCNQ and AsF₅ were doped, respectively. The conductivities of iodine- and bromine-doped polymers were 5.5×10-15 and 5.0×10-1' sicm, respectively, when the halogen vapor was absorbed for 12 h.