EPR spin probe study of polymer associative systems.

Molecular dynamics of polyacrylamide gels, polymeric micelles and hydrogel of polyacrylic acid and macrodiisocyanate was investigated by the ESR spectroscopy of spin probes. The local mobility in network junction of polyacrylamide gels is found to be essentially slower than that in the micelles created by the low molecular weight detergents and does not depend on the amount and length of hydrophobic groups (C9 or C12) in the polymer chain. The immersion of 10-30 mol.% of ionic monomers into the polymer chain (sodium acrylate) influences insufficiently on the local mobility of network junctions. In aqueous solutions, polystyrene-block-poly-(N-ethyl-4-vinylpyridinium bromide) block copolymers create polymeric micelles. The local mobility in the polystyrene core of the micelles is about twice as much as that in the solid polystyrene. Partially swellable polymer network in aqueous solutions was synthesized from polyacrylic acid and macrodiisocyanate. The local mobility in hydrophobic regions of the gel is substantially lower than that in the hydrophilic regions. It was concluded that the hydrophobic and hydrophilic regions and the local dynamics of them dictate practical application of the polymer associative systems.

Molecular mass characterization of polymers with strongly interacting groups using gel permeation chromatography-light scattering detection.

This work is aimed at studying dilute solution behavior and developing techniques for the proper Mr characterization of polymers with strongly interacting groups. In particular, we have studied ionomers based on poly(dimethylcarbosiloxane) with carboxylic groups and hydrophobically modified polyacrylamide and its charged terpolymer. Gel permeation chromatography-light scattering (GPC-LS) study of organosilicon ionomers allowed us to follow molecular mass distribution evolutions during approximately a week that evidenced the gradual dissolution of clusters formed in bulk polymers. The rate of this process depends on the polymer composition and its preliminary treatment. Observed aggregates arre found to be stable during the procedure of chromatographic analysis. For characterization of hydrophobically modified polyacrylamide and its charged derivatives, we have used aqueous NaNO3-acetonitrile mixed solvent. Fluorescence spectroscopy with pyrene as a probe did not reveal any hydrophobic association in this solvent in contrast to aqueous solutions. Reversed-phase retention as well as polyelectrolyte exclusion were suppressed at GPC analysis. GPC-LC and classical LS methods gave consistent results for uncharged and weakly charged polymers. In the case of highly charged and highly hydrophobic terpolymers LS results evidenced association, while OPC-LC gave credible Mr values. We can conclude that in the last case, the observed association was weak enough to be disrupted in the coarse of chromatography.