Fractionation

Abstract

Abstract Polymer fractionation techniques attempt to fractionate polymers according to specific characteristics of their microstructures as defined by their distributions of molecular weight, chemical composition, comonomer sequence length, tacticity, and long‐chain branching. Because of the heterogeneous nature of polymers, fractionation techniques are essential for understanding structure‐property relationships, polymerization mechanisms and kinetics, and polymer reaction engineering. In this entry, theoretical models to describe the microstructure of polymers are initially reviewed and used as a basis to understand the several polymer fractionation techniques described in the subsequent sections. Batch fractionation methods are covered next, including temperature variation and solvent/nonsolvent fractionation procedures. The recent technique of crystallization analysis fractionation (Crystaf), together with temperature rising elution fractionation (TREF), are reviewed as methods for fractionation by crystallizability. The well‐established technique for molecular weight fractionation by size‐exclusion chromatography (SEC) is covered next, followed by a section on the versatile field flow fractionation (FFF). Large‐scale fractionation of polymers is covered in the section for continuous polymer fractionation (CPF). Mass spectrometry, particularly matrix‐assisted laser desorption ionization coupled with time‐of‐flight analyzers (MALDI‐TOF) is the subject of the next section. Finally, a section in interaction chromatography and some other less general polymer fractionation techniques is followed by the concluding section on cross‐fractionation techniques.