Some applications of Raman spectroscopy in structural studies on poly(vinyl chloride)

Abstract

Raman spectroscopy has been used to obtain two types of structural information for poly(vinyl chloride) samples. The first is a more complete assignment of the carbon-chlorine stretching modes. The prediction of Moore and Krimm that the frequencies of the B1 mode of longsyndiotactic sequences in crystalline regions should differ because of correlation splitting in the infrared and Raman spectra has been verified. The problems involved in the quantitative interpretation of the Raman spectrum by use of computer resolution of overlapping bands to give information on the proportion of the various conformers of the syndiotactic and isotactic configurations, have been examined critically. The second application is the use of resonance Raman spectroscopy to characterize polyene sequences containing between 9 and 17 conjugated double bands in degraded PVC samples. Measurements on a commercial polymer degraded at 160 and 190°C show that the concentration of a conjugated polyene of a particular sequence length is a function both of the temperature and the overall degree of degradation. Preliminary results for thermally degraded samples of higher tacticity and for γ-irradiated specimens suggest that resonance Raman spectroscopy will be equally useful in these cases. The current limitations of the technique are discussed briefly.