Dielectric spectroscopy of binary polystyrene/poly[styrene-b-(ethylene oxide)] blends and ternary composites of polystyrene/poly[styrene-b-(ethylene oxide)] swollen with homopoly(ethylene oxide)

Abstract

The effect of incorporating poly[styrene-b-(ethylene oxide)], PS-b-PEO into PS/PEO composites has been examined microscopically and dielectrically. The addition of block copolymer stabilizes the dispersion of PEO in PS and can produce composites of PEO in PS in which the PEO domain size ranges from the size of the micelle core in binary PS/PS-b-PEO composites to larger PEO-swollen micelles to micron-sized phases of PEO stabilized by small amounts of PS-b-PEO. Dielectric spectra have been obtained as a function of frequency and temperature for binary composites of PS/PS-b-PEO and ternary composites of PS/PS-b-PEO/PEO, wherein the total content of PEO residues is held constant at 4.7% by weight. The dispersion of PEO in PS enables the observation of the full dielectric spectrum of the PEO phase. The dielectric spectrum of binary composites of PS/PS-b-PEO shows a predominant peak for the beta' relaxation of PEO chain segments covalently tethered to the glassy PS continuum. Ternary PS/PS-b-PEO/PEO composites show significant beta and beta' relaxations. The beta peak corresponds to that observed in pure PEO and in PS/PEO composites. The beta' peak corresponds to the higher temperature WLF type molecular relaxation observed in binary PS/PS-b-PEO composites and in PS/PEO composites. In the binary systems containing only PS and PS-b-PEO, the crystallinity of PEO is suppressed or disturbed. Accordingly, the upsilon and alpha peaks which present themselves in pure PEO and in PS/PEO composites are not observed.