On the selectivity of adsorption chromatography

Abstract

SYNOPSISIn this paper, the shape of chromatograms obtained by elution of copolymers with a mixture of solvent-nonsolvent of variable composition has been studied from a theoretical point of view. It is assumed that the thermodynamic quality of the mixture a t which the copolymer is eluted depends only on its composition and not on its mass and structure. If one characterizes the polydispersity in composition, assuming that each constituent obeys a molar mass distribution of the Zimm-Schulz type, one can draw the following curves: concentration of the copolymer versus eluant composition. They depend on three parameters, including composition of the copolymer and the polydispersity of each constituent. The most striking result is that the shape of the chromatogram changes dramatically when one increases the polydispersity of either constituents. For low polydispersities, one obtains a classical peak. For large polydispersities, the chromatogram has a minimum for the intermediate values of composition and presents peaks in the vicinity of the pure homopolymers. This can be explained easily by a qualitative argument.

Poly(n-butyl acrylate) Homopolymer and Poly[n-butyl acrylate-b-(n-butyl acrylate-co-styrene)] Block Copolymer Prepared via Nitroxide-Mediated Living/Controlled Radical Polymerization in Miniemulsion

“…The detection was performed using a UV detector (Waters 481) and an evaporative light scattering detector (DEDL 21, Eurosep). Details on the experimental conditions can be found in ref b.…”

“…The linear increase in M n after styrene addition, the complete shift of the SEC traces (both refractive index and UV traces), and the decrease in the M w / M n to 1.27 clearly indicated that chain extension was effective. Furthermore, liquid adsorption chromatography (LAC) 25 (Figure ), which performs separation according to the chemical composition, did not show any detectable poly( n -butyl acrylate) homopolymer, signifying efficient reinitiation by the first block. A different result was found when styrene was polymerized first; in particular, reinitiation was incomplete, even at high conversion in the second step, as demonstrated by the SEC and LAC analyses.…”