Journal of Polymer Science Part B: Polymer Physics, Vol.36, No.14, 2513-2523, 1998
Thermoplastic elastomer gels. II. Effects of composition and temperature on morphology and gel rheology
Thermoplastic elastomer gels (TPEGs) composed of a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and a low-volatility, midblock-compatible mineral oil have been investigated here to ascertain the effects of composition on TPEG morphology, and temperature on mechanical properties. Cryofracture-replication transmission electron micrographs reveal the existence of spheroidal bumps due to copolymer micelles, as well as a network of irregularly shaped, high-aspect-ratio features. Since the density of this network decreases with increasing oil concentration, these features are attributed to copolymer grain boundaries. Micellar periodicities are discerned from small-angle X-ray scattering as a function of copolymer concentration and compared with previously reported data from related systems. Dynamic rheological tests performed up to 140 degrees C indicate that the linear viscoelastic regime for these TPEGs decreases with both increasing copolymer concentration and temperature. A concentration-dependent thermal transition, signified by an abrupt reduction in the dynamic elastic modulus (G＇), has also been identified.
Keywords:COPOLYMER HOMOPOLYMER BLENDS, ANGLE X-RAY, TRIBLOCK COPOLYMER;BLOCK-COPOLYMER, NEUTRON-SCATTERING, DIBLOCK COPOLYMER;PHYSICAL GELATION, MOLECULAR-WEIGHT, BINARY BLENDS, SHEAR