Composition, copolymer, function retention volume

Composition Drift. Determinations of copolymer composition distribution by SEC with dual UV and RI detectors were developed by several researchers (1, 20-22). To exemplify that this methodology may only be capable of producing average composition data across a chromatogram as a function of retention volume V, results for samples of the diblock copolymer PS-PT are presented. The block lengths in samples of PS-PT were chosen such that the SEC peak for copolymer was well resolved from the PS prepolymer peak. 

When one of the constituents, A or B of a copolymer A-B, has an ultraviolet (UV) absorption and the other does not, a UV detector-refractive index (RI) combined detector system can be used for the determination of chemical composition or heterogeneity of the copolymer. A point-to-point composition, with respect to retention volume, is calculated from two chromatograms and a variation of composition is plotted as a function of molecular weight. The response factors of... 

Figure 11. Copolymer composition (Plv), average styrene sequence length (Ns) and number average molecular weight as function of the retention volume. Molar feed composition is 0.90. PS is the polystyrene calibration curve. Key , Mn A>...

Tri-block copolymers of MMA-styrene-MMA were characterized by SEC, TLC and PGC [79]. SEC was applied first to fractionate the copolymers according to molecular size. These fractions were subjected to PGC to obtain their composition. These fractions were also separated into block copolymer and homopolymers (PS and PMMA) by TLC. Using these three techniques, MMA (or styrene) percentage, and concentrations of block copolymer, PMMA homopolymer and PS homopolymer as a function of SEC retention volume could be obtained. 

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