Effect of hydration on the dynamics of polymeric cation exchangers and polymeric sorbent inferred from the Rayleigh scattering of Mössbauer radiation

Abstract

Dependences of the dynamics of hydrophilic polymeric nets of acrylate cation exchanger, sulfonated poly(styrenedivinylbenzene) cation exchanger, and hydrophobic poly(divinylbenzeneethylstyrene) sorbent on the degree of hydration were studied by the Rayleigh scattering of MOssbauer radiation (RSMR). Dependences of the integral elastic fraction of RSMR of the polymer--water systems on the water/polymer mass ratio were determined. In the case of the cation exchangers, a considerable decrease in the elastic fraction of RSMR of the polymer during hydration was established. A considerable increase in the mobility of the nets indicates their transition from a glassy state to an elastic state. It was established that the intramolecular mobility of the hydrophobic polymeric sorbent remains unchanged during its hydration, and it contains water clusters with the nonzero elastic fraction of RSMR in its finest pores.Key words: Rayleigh scattering of M6ssbauer radiation, dynamics of polymers, polymeric ion exchangers, polymeric sorbents, hydration.The study of the dynamics of polymers is motivated by the relation between their dynamics and important functional properties. This concerns completely a special class of reactive polymers, viz., polymeric ion exchangers.Previously, 1-4 it has been established by M6ssbauer spectroscopy that the hydration of the three-dimensional polymeric net of an acrylate cation exchanger results in its transition from the glassy to the elastic state with very intense intramolecular motions. The frequency and amplitude parameters of these motions were studied quantitatively, and their strong dependence on the crosslinkage concentration of the polymeric net was established. In these works, the MOssbauer isotope 57Fe was introduced into the ion exchanger to form a strong complex with functional groups (--RCOO-)2Fe3+A -. In this case, the dynamics of the Fe atom reflected the dynamics of the fragment of the polymeric net. The necessary presence of functional groups, which bind strongly the atom-label, is the natural restriction of this approach. In addition, the effect of a metal ion on the dynamics of the polymeric net and the dynamic heterogeneity of the net cannot be ambiguously separated in the strong dependence of the mobility on the number of metal ions introduced. When the M6ssbauer probe is used, its mobility is mainly determined by the microstructure rather than the mobility of the net of the solvated ion exchanger. 5,6 Therefore, an alternative approach is very important: the study of the dynamics of a polymer--water (solvate) system by the Rayleigh scattering of M~ssbauer radiation (RSMR). The possibility to study any substance in the absence of M6ssbauer atoms is a great advantage of the method, although there is some uncertainty in separating the contributions of components of the two(multi)-component system to the integral spectrum of the scattered radiation.In this work, we present the first results of the study of the dynamics of the polymeric ion exchanger--water and polymeric sorbent...