Temperature rising elution fractionation

Abstract

An outline is given of the development of temperature rising elution fractionation (TREF) technique for polymer separation on the basis of crystallizability. The TREF technique has found application mainly in the area of analysis of semi-crystalline polyolefins and its development has been significantly influenced by the desire to establish the structure of linear low density polyethylenes. These materials exhibit an unusually broad distribution of comonomer which can be readily explored by TREF. Systems have been developed which can provide fractionation on a preparative scale, where recovery of fractions for further analysis is desirable and more recently on a small scale, where rapid analysis using detectors provide refined crystallizability distributions. A description is given of these fractionation systems along with a discussion of the separation mechanism and the significance of controlling the crystallization step to achieve fractionation efficiency.

Application of TREF is discussed with reference to low density polyethylenes made by both the high and low pressure process, ethylene vinyl acetate copolymers and poly-propylenes. The value of TREF for analysis of polymer blends is emphasized along with the potential for cross-fractionation combining TREF with a molecular weight fractionation for detailed analysis of polymer structure. Finally the point is made that TREF is becoming much more widely used and accepted as a technique for structural evaluation. Further improvements in instrumentation and techniques for controlling the crystallization step are expected. These will further enhance the usefulness of TREF and pave the way for its greater use both in the area of polyolefins as well as for other crystalline polymer systems.