Practical use of intrinsic viscosity for polyethylenes

Abstract

AbstractAlthough usually derived from measurements at several concentrations, intrinsic viscosity (IV) can be determined with good precision from a single measurement. IV tends to be a regular and distinct function of melt index (MI) for each family of high‐density polyethylenes. The tendency to regularity suggests a use in routine control, uniform production being marked by a small scatter about the IV–MI line. The distinctiveness marks one family of medium high and high‐density resins from another, and becomes a rapid means of identifying the production method of a resin. Further, IV at a given MI correlates roughly with properties, and can be used to characterize a resin. These attributes of the IV–MI relationship arise from the correlation of IV a t a given MI with width of molecular weight distribution. Such width varies considerably among commercial high‐density polyethylenes, causing a commensurate variation in IV. Among low‐density polyethylenes the IV–MI relationships is less useful, being confused by long‐chain branching.