Fixation by H-bonding of ligands in polymer coils

The stability constants of H-bonds between phenols and the ester groups of polyethylmethacrylate (PEMA) in CCl4 determined by IR measurements, are of the same order of magnitude as those of the phenols with the low-molecular model substance ethylisobutyrate. In absence of additives, the cloud points at 25 degree C of PEMA (Mw=258000) in CCl4-n-hexane mixtures are fairly well predicted by the equations of Huyskens et al. The presence of phenols displaces these cloud points towards higher values of the relative mole fraction of the cosolvent. This is also the case when acetone is used as additive. Beyond the cloud point, viscosity measurements show that practically no polymer coils remain in the supernatant liquid. However, after the phase separation, the additives behave in a completely different way. Dipolar measurements show indeed that the concentration of acetone in the supernatant liquid is of the same order as in the solution before the precipitation, whereas the phenol molecules are predominantly found in the precipitated flakes. This illustrates the fundamental difference between non-specific dipole-dipole interactions and specific intermolecular forces like H-bonds, whose characteristics were extensively studied during more than thirty years by Lucjan Sobczyk and his coworkers.