SynopsisA description is given of an analytical temperature-rising elution fractionation (TREF) system for the purpose of determining short-chain branching (SCB) or copolymer distributions in polyethylenes and ethylene copolymers. The system achieves fractionation on the basis of crystallhbility and is shown to be very little influenced by molecular weight in the normal high polymer range. Sample preparation by slow cooling from relatively dilute solution followed by continuous elution with a simultaneous and fairly rapid rate of temperature rise proves to be an efficient fractionation process. An on-line detector and data system allows application of a calibration curve to give realistic SCB distribution data in a convenient manner. The potential value of the TREF technique for providing structural information is illustrated by examples which include low-density high-pressure resins made by both tubular and autoclave reactors, high-and low-density resins made by lowpressure processes, and copolymers of ethylene with vinyl acetate and ethyl acrylate.

A method is described and a computer program outlined whereby gel‐permeation chromatographic analysis of fractions from gradient‐elution fractionation of branched polyethylenes provides a complete molecular weight evaluation of each fraction and the parent resin. The procedure involves the use of the universal calibration concept of Benoit et al. in a way that eliminates the ambiguities present in attempts to apply it directly to whole polymers. The resultant molecular weight data for fractions, when related to their solution viscosity and low‐shear melt viscosity and to their infrared analysis, provides a total structural evaluation of a branched polyethylene resin, including molecular weight molecular weight distribution and the distribution of both long‐and short‐chain branching. The potential of this method for providing a comprehensive structural evaluation of branched polyethylene is illustrated by examples of its application in the analysis of some commercial resins.