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Dual detection HPSEC system as an aid in copolymer characterization

Compositional heterogeneity is one of the essential factors controlling the physical and physico-chemical properties of copolymers ; its determination is in most cases a rather difficult and challenging scientific task. The overall composition of a copolymer comprising two kinds of repeating units can be determined as a function of molecular mass by the dual detector high performance size exclusion chromatography (HPSEC) technique. The common combination of the refractive index (RI) detector with the UV spectrophotometer can be applied if at least one of the monomer units absorbs at a suitable wavelength and if the UV-spectra of both components are sufficiently different. In this paper, synthesized random copolymers of styrene and methyl methacrylate were dissolved in tetrahydrofuran and characterized by the RI-UV HPSEC technique, at the UV wavelength of 254 nm. Home made software and a corresponding hardware interface were used for the equipment control, data acquisition, data processing and calculation. The obtained results show that the technique is capable for fast, routine determination of average copolymer composition. There is no significant variation of chemical composition with molecular mass for investigated copolymers with lower polystyrene content. For copolymers rich in polystyrene, chemical composition varies with molecular mass. In this case, calculated apparent mass fractions of styrene may exceed 100%, and this is explained by the presence of small quantities of low-molecular-mass styrene hompolymer.

Size Exclusion Chromatography; Dual Detection; Styrene - Methyl Methacrylate Copolymers

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