EPR STUDY OF CHAIN ROTATIONAL-DYNAMICS IN DILUTE AQUEOUS-SOLUTIONS OF SPIN-LABELED POLY(METHACRYLIC ACID) AT DIFFERENT DEGREES OF NEUTRALIZATION

Spin-labeled poly(methacrylic acid) (SL-PMA) was synthesized and EPR spectra of its dilute aqueous solutions were measured at different degrees of neutralization over the temperature range 272-333 K and analyzed. The temperature dependence of parameters characterizing the segmental rotational mobility of SL-PMA and the internal rotation of the spin-label relative to the polymer chain were determined by fitting line shapes of the experimental EPR spectra to the simulated ones. The simulated EPR spectra were calculated by use of axially symmetric Brownian rotational diffusion for modeling the rotational diffusion of the spin label. The determined apparent activation energies of SL-PMA segmental rotational diffusion are discussed in connection with both its conformation in dilute aqueous solution and the activation energy of the viscous flow of the solvent used.