Separation and characterization of low-conversion poly(styrene-co-methyl methacrylate) by liquid adsorption chromatography

Poly(styrene‐co‐methyl methacrylate) copolymers of narrow chemical composition distributions were separated according to composition by linear gradient elution at column temperatures between 10 and 80°C using silica gel as an adsorbent. The initial mobile phase was a mixture of chloroform and ethanol (99.0 : 1.0, v/v) and the final one (95.5 : 4.5). The relationship of retention volume and the composition of the copolymers was obtained. Higher column temperature (and/or less ethanol content in the mobile phase) is preferable for the separation of copolymers having less MMA and vice versa. Molecular weight dependence on retention volume was not observed. The chromatographed copolymers were still chemical heterogeneous: the compositional difference of the front and rear halves of an adsorption chromatogram of a copolymer was 2.1 %. The front half had a higher styrene content and lower molecular weight averages than those for the rear half of the peak. This separation method was reproducible and the relative standard deviation was about 0.6%. Recovery of fractions was 98.2% by isocratic elution and 96.4% by gradient elution.