Size exclusion behavior of polymers in amide solvents .3. Elution characteristics of acrylic polymers in N,N-dimethylformamide

Nonexclusion effects of acrylic polymers in the size exclusion chromatography using DMF as the mobile phase were investigated. A poly(methyl methacrylate) sample containing sulfate terminal end groups presented marked differences in the elution behavior when compared with the corresponding neutral sample, as in the case of polyacrylonitrile (PAN). It was observed that there is an unexpected small retention in the PS-DVB column and a large peak was detected by UV at 280 nm, which was not detected by the RI detector. The deionization of the DMF extinguished the peak detected by UV and shifted the retention volumes to higher values, but it did not affect the shape and position of the neutral polymer peak. A very strong adsorption effect was shown in the SEC of poly(acrylic acid) (PAA) in deionized DMF. The activity of the sites on the PS-DVB gel in deionized DMF was suppressed by saturation through successive injections of PAA. The elution peculiarities were ascribed to the electrostatic interaction between the charged polymer chains and the ionic species from DMF degradation. The addition of a small amount of LiBr to DMF inhibited the interactions completely. (C) 1997 Elsevier Science Ltd.