THERMOPLASTIC ELASTOMER GELS - I - EFFECTS OF COMPOSITION AND PROCESSING ON MORPHOLOGY AND GEL BEHAVIOR

Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(eth ylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated at different o il concentrations to ascertain the effect of composition on TPEG morph ology and mechanical properties. The impact of thermal processing is a lso examined by comparing gels thermally quenched to 0 degrees C or sl owly cooled to ambient temperature. Transmission electron micrographs reveal that gels with 70 to 90 wt % oil exhibit styrenic micelles meas uring ca. 24 nm in diameter. Variation in composition or cooling rate does not have any perceivable effect on micelle size or shape, whereas the rate at which the gels are cooled influences the extent of micros tructural order and the time to rupture (t(R)) at constant strain. Dyn amic rheological testing confirms the presence of a physically crossli nked network at TPEG compositions ranging from 70 to 90 wt % oil, inde pendent of cooling rate. Results presented here suggest that the dynam ic elastic shear modulus (G') scales as t(R)(alpha), where a varies fr om 0.41 to 0.59, depending on cooling rate. (C) 1998 John Wiley & Sons , Inc.