CONSIDERATIONS FOR RAMAN-SPECTROSCOPIC DETERMINATION OF POLYENE LENGTH DISTRIBUTION IN DEGRADED POLY(VINYL CHLORIDE)

Practical complications in the quantitative Raman spectroscopic determination of the polyene sequence length distribution in degraded poly(vinyl chloride) samples were found. If samples are measured directly, i.e. without dissolving them, the distribution of polyenes changes during the Raman experiment if power densities above 20 W/mm2 are used. Lower power densities or short exposure times (<1 min) must be used to avoid these effects. The direct method turned out to be an appropriate method for the quantitative determination of the polyene length distribution in lightly degraded poly(vinyl chloride) samples (<0.05 % HCl loss). If the samples are dissolved in tetrahydrofuran, the influence of laser power is negligible. However, in that case other problems are encountered; solutions must be stored in a cooled state and in the dark in order to avoid disappearance of the polyenes. Moreover, the solution process results in an altered polyene sequence distribution. The tetrahydrofuran method turned out to be a quick and convenient way to obtain information about the polyene sequence distribution for samples with relatively high degradation levels (>0.05 % HCl loss).