GPC study of ethylene-propylene copolymers combined with viscometry and IR spectroscopy

Summary By combining GPC fractionation with IR spectroscopy of ethylene-propylene copolymer (EP) samples, it has been shown that copolymer composition of EP's used in this study does not dep-end on molecular weight. Thus, contrary to earlier investigations by others, molecular weight distributions (MWD) and averages of EP's have been determined by using only experimental data such as GPC traces, universal calibration curve of GPC, and intrinsic viscosities. A comparative study has been carried out by using the MV method (called median value method) and the method of Ogawa and Inaba (OI method) for determination of MWD's and molecular weight averages of EP's. Application of the MV method results in lower molecular weight averages than the use of the equations proposed by Ogawa and Inaba for calculation of Mark-Houwing constants of EP's. However, polydispersities were found to be the same in both methods. The MV method also yields composition depending reliable pairs of Mark-Houwink constants, a and K, for EP's in 1,2,4-trichloro-benzene at 135 °C.