Polystyrene-polyisoprene blends : a spin-label study
Polystyrene (PS) carrying a terminal nitroxide group was synthesised by anionic polymerisation. The ESR spectra of the PS in bulk and in blends with polyisoprene (PIP) recorded over a range of temperatures indicate that the motional freedom of a proportion of the labelled PS chain ends is enhanced by the presence of PIP especially at elevated temperatures (above ca. 400K). The possibility that this effect is due to a trend towards macroscopic miscibility between the two homopolymers at temperatures in the region of 400K is ruled out by a range of experiments including differential scanning calorimetry and interfacial tension measurements. It is concluded that in PS/PIP blends there is a greater than average concentration of PS chain ends in the PIP-enriched environment of the phase boundaries. This work provides the first experimental verification of the prediction, based on thermodynamic considerations, that in immiscible blends of polymers chain ends are located in preference to internal segments at the interfacial region (interphase).