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DUAL DETECTION SYSTEM IN HPSEC OF COPOLYMERS

Determination of the compositional heterogeneity of copolymers, in addition to molecular characterization common to homopolymers is an essential factor controlling the physical and physico-chemical properties of this class of materials. The overall composition of copolymer comprising two kinds of repeating units can be determined as a function of molecular mass by a dual ( UV and RI ) detector HPSEC technique. The common combination of the RI with the UV detector can, however, only be applied if at least one of the monomers absorbs at a suitable wavelength and if the UV-spectra of both components are sufficiently different. Wavelengths at which absorbance of the copolymer parts are monitored must be chosen to maximize the difference in molar absorbance of the parts. The signal of the RI and UV detectors of the HPSEC equipment must be strictly proportional to the concentration of the copolymer parts. Beside the compositional heterogeneity, depending on the copolymer type ( alternating, statistical, block and graft ) some additional parameters ( grafting efficiency, graft ratio, frequency of graft chains along the polymer backbone ) could be determined by this technique. Syntesized random copolymer of styrene and methyl methacrylate were dissolved in tetrahydrofuran and characterized by the mentioned technique using 254 nm wavelength of UV detector. For the equpment control, data acquisition, data processing and calculation a home- made software and hardware interface were used.

dual ( UV and RI ) detector HPSEC technique; copolymers

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