Modification of a thermoplastic elastomer gel through the addition of an endblock-selective homopolymer

Abstract

Addition of a midblock-selective oil to an ABA triblock copolymer with a rubbery B-midblock and thermoplastic A-endblocks yields a thermoplastic elastomer gel (TPEG) if the oil constitutes the majority blend constituent and a physically crosslinked network, responsible for solid-like mechanical properties, is retained. These blends typically exhibit a micellar morphology in which the micellar cores are composed of the oil-incompatible A-endblocks. Since the micelles serve as crosslink sites, the properties of TPEGs depend on (i) the intrinsic characteristics of the solid-state endblocks, and (ii) the degree to which the micelles interact through bridged and looped midblocks. In this work, a poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer and an aliphatic oil are used to prepare TPEGs into which poly(2,6-dimethylphenylene oxide) (PPO), a styrene-compatible homopolymer, is added. The morphologies and bulk properties of these ternary systems are examined by electron microscopy, viscometry, and dynamic rheology. A slight increase in the PPO content in these TPEGs promotes increases in micelle size, confirming that the PPO primarily resides within the micelles, and disordering temperature, signified by an abrupt change in rheological properties. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1863–1872, 1999