Measurement of the absolute molecular weight and molecular weight distribution of polyolefins using low-angle laser light scattering



By connecting a low-angle laser light scattering photometer (LALLSP) on line with a high-temperature gel permeation chromatograph (GPC), molecular weight distributions were determined for three polyethylene standards (two high density and one low density) without resorting to column calibration procedures. In addition, the absolute weight-average molecular weight and second virial coefficients of four polyethylene standards (three high density and one low density) were obtained using low-angle laser light scattering. The molecular weights measured were in excellent agreement with those specified by the National Bureau of Standards. For the low density material, a microgel fraction was detected by the on-line LALLSP but not by the conventional GPC detector. This resulted in a z-average molecular weight of over 3 × 106 daltons, an order of magnitude greater than that determined by conventional GPC techniques.