Molecular dynamics and heterogeneity of the styrene-acrylonitrile copolymers as viewed by electron spin resonance

Molecular mobility and heterogeneity of statistical and alternating copolym ers of styrene and acrylonitrile have been studied in the wide temperature range by the ESR spin probe method using two nitroxyl radicals, Tempo and T empone. The temperature at which the maxima separation becomes 5 mT decreas es with increasing styrene content. At higher temperatures above the glass transition temperature the copolymers with the smaller amount of styrene re flect motional heterogeneity. The motional difference between the statistic al and alternating copolymers of a similar composition are reconciled on th e basis of the sequence structure of copolymer chains. The packing of segme nts and the formation o motionally different domains can be explored by the adequately chosen probe even i the homopolymers have very similar glass tr ansition temperature but differ in the polar and packing features.