THE ORIGIN OF BANDSHAPES AND INTENSITIES OF POLYENE RESONANCE RAMAN BANDS FROM DEGRADED POLYURETHANE FOAM-BACKED POLY(VINYL CHLORIDE) SHEETAT DIFFERENT EXCITATION WAVELENGTHS

A new method has been developed that uses model u.v./visible absorptio n spectra to determine the relative resonance enhancement factors and the ranges of polyene lengths that contribute to a particular resonanc e Raman spectrum from a thermally degraded poly(urethane) foam-backed poly(vinyl chloride) sheet. Resonance Raman spectra were recorded usin g Microline Focus instrumentation with 514.5, 488.0, 457.0 and 632.8 n m excitation. The individual polyene nu(2) resonance Raman bands contr ibuting to the observed nu(2) resonance Raman band have been determine d and polyene concentration profiles have been calculated. Interpretat ion of the data shows that polyene propagation is the dominant mechani sm in the degradation. Detailed modelling of the 514.5 nm excitation d ata, over the full range of degradation times, indicates an inverse re lationship between concentration and polyene length. This new result s uggests that there is no maximum length to which a polyene propagates in this system.