Phenylacetylene metathesis polymerization mechanism

A striking feature of the stereoregular polyacetylenes is their simple NMR spectral patterns, which facilitates elucidation of the polymerization mechanism as well as the polymer structure. A co-polymer of phenylacetylene with partly G-labeled phenylacetylene (Ph G= GH) shows two doublet carbon signals with /i3c-i3C of 72 Hz, indicating the presence of G= G bond in the polymer backbone.This is a clear indication of the insertion mechanism instead of the metathesis pathway. 

Pfleger et al. [369] have studied photoconduction in undoped poly(phenylacetylene) which they prepared by coordination polymerization of phenylacetylene using the metathesis catalyst WOCU/Pl Sn. The polymer thus obtained was predominantly in the c/5-transoidal form, as demonstrated by IR spectra, and had a molecular weight of (A/ ) 91 000. The photoconduction threshold has been detected at 410 nm, although absorption of the film extended up to 550 nm. It is suggested that the mechanism of photogeneration is intrinsic by its nature. The formation of initial charge carrier pairs occurs by an exciton autoionization process [38]. From the temperature dependence, as well as Irom the field dependence of the quantum yield, the pair separation distance was established to be ca 2.2 nm. 

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