Abstract
Polystyrene (PS) samples carrying terminal or in-chain nitroxide spin labels have been blended with poly(vinyl methyl ether) (PVME) in varying proportions and their electron spin resonance (ESR) spectra recorded over a range of temperatures. The spectra are mainly of the slow-motion type but reflect the plasticizing influence of the PVME on the PS. However, the spectra of the blends containing end-labelled PS (but not those of in-chain-labelled PS) develop a second motionally-narrowed component at a particular temperature T f which is dependent on the proportion of PVME present. As with the cloud point T c , T f increases with the proportion of PS in the blend, but T f is about 60°C below T c . It is proposed that T f is the temperature at which the ESR technique is capable of detecting the onset of phase separation. Since the spin-label experiment responds to events at a micro or molecular level, T f is lower than T c which is essentially a macroscopic quantity.
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