The IR absorbances at 1465 and 1378 cm−1 formed the basis of an infrared method for estimating the ethylene/propylene ratio in EPM polymers. Calibration curves were set up for both self-supporting and silver chloride supported films of ASTM EPM polymers. The adequacy of the calibration curves was verified by 1H and 13C NMR data and by testing the methods on several commercial polymers. The self-supporting film method provided more reproducible data than the silver chloride film method. Even so, the confidence intervals for predicting the composition of new polymers were rather broad. They could be reduced to about ±2 wt.% ethylene on polymers of 40 to 70 wt.% ethylene by running five analyses. We have illustrated some of the problems which face the analytical chemist in setting up calibration curves with particular focus on the quality of new data arising from the calibration.
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Johnson-Plaumann et al. (1986) studied this question.