Fundamental study of the separation of homopolymers from block copolymers by liquid chromatography with preloaded adsorption promoting barriers.

ABSTRACT

A fundamental study of the separation of homopolymers from polystyrene-block-polymethylmethacrylate (PS-b-PMMA) by liquid chromatography with preloaded discrete and continuous adsorption promoting barriers was performed. The impact of barrier composition on the separation of block copolymers (BCP) was studied by a dual detection (ultraviolet (UV) and evaporated light scattering (ELSD) detectors) system that enabled monitoring both barrier composition and BCP separation simultaneously. The separation of homopolymers from BCP by preloaded discrete adsorption promoting barriers was validated via a series of control experiments by blending known amounts of homopolymers PS or PMMA with PS-b-PMMA, and the resulting chromatograms were free from co-elution of homopolymers and BCP. Quantitation of homopolymers and BCP by ELSD was also demonstrated. The influence of BCP chemical composition on the separation by preloaded discrete adsorption promoting barriers was investigated. Results showed a PS-b-PMMA having 90wt% PMMA co-eluted with homopolymer PMMA, whereas PS-b-PMMA samples having lower amounts of PMMA block could be separated from homopolymer PMMA, successfully. Attempts at using a preloaded solvent gradient for separating homopolymers from block copolymers were unsuccessful. UV detection of the solvent gradient revealed significant deviation in solvent composition compared to the nominally loaded gradient. This deviation was due to the interaction of strong desorption solvent with column stationary phase. As such, the barrier composition in the preloaded gradient method was not as expected. Therefore, one can obtain undesired separation results by preloaded solvent gradients.