Columnar Formation from Polyethynylbenzene and Poly-(p-Methylethynylbenzene) Polymerized Using [Rh(norbornadiene)CI]2 as a Catalyst. An X-ray and ESR Study

Abstract Stereoregular polymerization of p-methylethynylbenzene (MEB) was successfully performed using a [Rh(norbornadiene)CI]2 catalyst in alcohol and triethylamine. Polymers which have a cis-transoid structure were selectively formed in fairly high yields. The structure and properties of the resulting polymers were compared with those of polyethylnylbenzene (PEB) by means of x-ray diffraction and ESR techniques. The data showed that both pristine amorphous polymers are converted to pseudohexagonal structures called columnar when they were treated with toluene at room temperature. The line width, ΔH msl in the ESR spectrum of PMEB polymer was found to be increased from 10.5–12.5 gauss to 13.1–15.8 gauss when the solvent was changed from alcohols, e.g., ethanol or tert-butanol, to cyclic alcohols, e.g., cyclopentanol. The increase of the observed ΔH msl was explained in terms of magnetically inhomogeneous broadening arising from heterogeneous aggregations of radical spins in the columnar polymer phase.