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

Spin-labeled poly(acrylic acid)(SL-PAA) was synthesized and electron p aramagnetic resonance (EPR) spectra of its dilute aqueous solutions we re measured at different degrees of neutralization a in the temperatur e range 273-353 K. The temperature dependence of parameters characteri zing the segmental rotational mobility of SL-PAA and the internal rota tion of the spin label relative to the polymer chain were determined b y simulating the line shapes of the experimental EPR spectra. The segm ental rotational dynamics of SL-PAA was found to be nearly independent of its degree of neutralization. The absence of the methyl group is p robably responsible for higher segmental rotational mobility of SL-PAA at all degrees of neutralization and in the entire temperature range studied, when comparing with spin-labeled poly(methacrylic acid) (SL-P MA) under the same conditions. SL-PAA forms strong complexes with both poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP) in aque ous solutions at alpha = 0.0 and 0.1. The complexes immediately precip itate from the solution under our experimental conditions. Complexatio n of SL-PAA neutralized to higher degrees (alpha = 0.2-1.0) with PEO o r PVP in aqueous solutions was not observed.