SEGMENTAL MOBILITY OF SPIN-LABELED POLY(METHACRYLIC ACID) IN COMPLEXES WITH ALKYLTRIMETHYLAMMONIUM BROMIDES

The segmental mobility of spin-labeled poly(methacrylic acid) in aqueo us solutions with various pH values and in complexes with alkyltrimeth ylammonium bromides was determined by comparing the experimental and c alculated EPR spectra. The theoretical spectra were calculated using a model according to which the spin label participates in the motions o f two types. (i) slow Brownian rotations performed together with a mac romolecular segment and (ii) fast intrinsic oscillations relative to t he polymer chain. In aqueous solutions, the segmental mobility of PMAA increases on passing from weakly acidic (pH 6) to alkaline (pH 9) me dium. This is related to an increase in the degree of ionization of th e acid and a change in the conformation of macromolecules from ''compa ct'' (stabilized by a system of hydrogen bonds) to ''uncoiled (typical of a strongly swelled statistical polymer coil). The formation of sol uble polyelectrolyte complexes at pH 6 leads to increasing segmental m obility of the macromolecules as a result of breakage of the compact c onformation of spin-labeled PMAA. At pH 9, the formation of the polyel ectrolyte complexes has virtually no effect on the segmental mobility of the polymer. These laws apply to all the alkyltrimethylammonium bro mides studied and are valid within the entire range of compositions in which the complexes remain soluble. The formation of insoluble stoich iometric complexes leads to a sharp drop in the segmental mobility of spin-labeled PMAA.