ANALYSIS OF BLOCK COPOLYMERS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY UNDER CRITICAL CONDITIONS

The complete chromatographic characterization of block copolymers (molecular weight versus chemical composition) is an important problem in polymer chemistry. The experimental validity of the concept of so-called "chromatographic invisibility", predicted theoretically by Gorbunov and Skvortsov on the basis of the phenomenon of critical conditions known in liquid chromatography, was examined. The theoretical approach predicts the possibility of one component of an A-B block copolymer being eluted under gel permeation chromatographic conditions, whereas the size of the alternate "invisible" component exerts no effect on the overall elution profile of the block copolymer. This applies only when special thermodynamic conditions, i.e., eluent composition and temperature, are fulfilled, where the distribution coefficient K is unity, regardless of molecular weight. Block copolymers of poly(styrene-methyl methacrylate) and poly(styrene-tert.-butyl methacrylate) were used as examples with binary and ternary mixtures of acetonitrile-dichloromethane, methanol-chloroform, tetrahydrofuran-dichloromethane and tetrahydrofuran-dichloromethane-hexane as eluents for chromatography under critical conditions on wide-pore silica gel in narrow-bore columns.