USE OF RHEOLOGICAL MEASUREMENTS TO ESTIMATE THE MOLECULAR-WEIGHT DISTRIBUTION OF LINEAR POLYETHYLENE

An important characteristic of a polymer is its molecular weight distr ibution (MWD). The MWD affects its processing characteristics and its solid state performance. The traditional analytical method for determi ning MWD is gel permeation chromatography (GPC). However, GPC results depend strongly on the skill and experience of the operator and are no t sensitive to small amounts of high molecular weight material that ca n have an important effect on processing and product properties. It is known that rheological properties depend on MWD, and it has been prop osed that viscosity or complex viscosity data can be used to infer the MWD for commercial polymers. Although there has been some controversy as to whether this is feasible, recent results of Shaw, Tuminello, an d others indicate that for linear polymers this is, in theory, possibl e. However, limitations in the accessible frequency range, as well as inevitable experimental errors, pose serious barriers to the use of su ch a procedure. We have investigated the severity of these barriers an d have shown that within certain limits, complex viscosity data can be used to infer a realistic MWD for linear polyethylenes. (C) 1996 Soci ety of Rheology.