TRANSPOLYACETYLENE ON SODIUM AND CESIUM MORDENITES - A RESONANCE RAMAN-SPECTROSCOPIC STUDY

Sodium and cesium mordenite (denoted NaM and CsM, respectively) were i nvestigated as potential catalysts for the synthesis of polyacetylene ((CH)x). Both were successful in initiating polymerization of purified gaseous acetylene at room temperature as evidenced by Raman spectrosc opic studies. The polyacetylene synthesised in this way exhibited reso nance enhancement of the polyene skeletal vibrations. trans-Polyacetyl ene, but no cis-(CH)x, was detected. As no apparent coloration of the NaM and CsM substrates accompanied the formation of trans-(CH)s it was concluded that only small quantities of the polymer were present. The number of conjugated double bonds was estimated from the frequencies of the Raman active C-C and C=C stretching vibrations, and it was show n that the trans-(CH)x formed on CsM has a distribution of conjugation lengths ranging from less than 6 to at least 30 double bonds. The pol yacetylene formed on NaM was significantly shorter and was produced in lower yields than that synthesized on CsM. ''Sliced'' resonance excit ation profiles of polyacetylene formed on CsM were obtained using near ly 40 different excitation wavelengths and these confirmed that the ad sorbed trans-(CH)x was composed of segments having a distribution of c onjugated lengths. The architecture of the mordenite pore system permi tted only a single polymer molecule per channel, there by preventing c ross-linking. Raman spectroscopic studies of the effects of exposure t o air revealed that progressive oxidative degradation occurred with a reduction in the number of conjugated double bonds.