SEPARATION AND DETECTION OF STYRENE-ALKYL METHACRYLATE AND ETHYL METHACRYLATE-BUTYL METHACRYLATE COPOLYMERS BY LIQUID ADSORPTION CHROMATOGRAPHY USING A DICHLOROETHANE MOBILE PHASE AND A UV DETECTOR

Styrene (S)-methyl methacrylate (MMA), S-ethyl methacrylate (EMA) and EMA-n-butyl methacrylate (BMA) copolymers were separated according to chemical composition. Silica gel was used as the stationary phase and a mixture of 1,2-dichloroethane (DCE) and ethanol as the mobile phase. DCE was transparent at wavelengths over 230 nm and methacrylate homopolymers and copolymers could be monitored with a conventional UV detector at 233 nm. The molar absorption coefficients for both PS and PMMA at 233 nm were nearly equal and the chromatograms obtained at this wavelength reflected the relative amounts of the copolymers with different chemical compositions. A mixture of S-MMA copolymers having different compositions and PMMA was separated by a gradient elution method at constant column temperature. The initial mobile phase was a mixture of DCE and ethanol (99.0:1.0, v/v), and the ethanol content was increased to 5.0% in 20 min and then to 10.0% in another 5 min or to 10.0% in 20 min. The copolymers of S-MMA and S-EMA having higher styrene contents eluted earlier and the elution of the copolymers was in order of decreasing styrene content. Therefore, the chemical composition of the copolymers in a mixture can be determined directly from the chromatogram by knowing the retention volume of each copolymer. A mixture of PEMA, PBMA and their copolymers was also separated by a similar method. PBMA eluted earlier than PEMA. The affinity of the EMA component to the surface of silica gel was assumed to be stronger than that of the BMA component.