An electron spin resonance study of poly(α‐ethynylnaphthalene) polymerized with [Rh(norbornadiene)Cl]2 and WCl6 as catalysts

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Abstract
Poly(α‐ethynylnaphthalene)s (PENAPs) obtained with the Rh complex [Rh(norbornadiene)Cl]2 as a stereoregular polymerization catalyst of monosubstituted acetylene monomers and WCl6 were studied by using the electron spin resonance (ESR) method to inspect the geometrical structure with respect to the CC bond in the main chain where π‐radicals called solitons may be stabilized in the conjugated polymer chain. In PENAP obtained as the immobile unpaired electrons were found to be stabilized in the polymer chain, indicating a short and restricted conjugated chain, i. e., formation of a cis‐transoid polymer. In PENAP obtained with WCl6 as catalyst more mobile unpaired electrons were found to be stabilized in the conjugated polymer chain not only at room temperature but also at lower temperature, indicating the presence of a π‐conjugated main chain, i. e. of a trans‐transoid polymer. Moreover it was found, interstingly, that the clearly resolved ESR spectrum with the hyperfine structure (solitin) could be observed at higher temperature, i. e., ca. 300°C.