Separation of poly(styrene–methyl methacrylate) block copolymers by liquid adsorption chromatography

Block copolymers P(S-b-MMA) prepared by using polymeric peroxide as an initiator were separated into three peaks using silica gel as an adsorbent and a mixture of chloroform and ethanol as the mobile phase. The first peak included both polystyrene homopolymer and P(S-b-MMA), the second peak appeared to be P(S-b-MMA), and the third consisted of P(S-b-MMA) and poly(methyl methacrylate) homopolymer. These results suggest the presence of three different block copolymers in composition and/or in structure. By removing the two homopolymers, it was found that the P(S-b-MMA) sample prepared in this work consisted of two components of equal amount: One was a block copolymer having a smaller MMA content and smaller molecular weight averages and the other having a higher MMA content (similar to the monomer feed ratio) and higher molecular weight. Besides these two components, one minor copolymer, which might be different from these two components but rather similar to the first one in both composition and molecular weight, appeared between these two peaks in a liquid adsorption chromatogram. These three components had both composition and molecular weight distributions.