Elizabeth A. Wilder

The molecular structure and intermolecular interactions of 1,3:2,4-dibenzylidene-D-sorbitol

The 1,3(R):2,4(S)-dibenzylidene-D-sorbitol (DBS) molecule is a low molar mass organic gelator (LMOG) that is capable of hydrogen-bonding with itself. As a consequence, DBS molecules self-organize into nanofibrillar networks at relatively low concentrations in a wide variety of organic solvents and polymers. In this work, molecular mechanics and molecular dynamics simulations were conducted to elucidate the equilibrium structure of DBS and the molecular interactions that govern DBS self-assembly. Molecular mechanics calculations performed on single DBS molecules with Cerius2 and InsightII software reveal that the phenyl rings tend to adopt an equatorial position and that the pendant hydroxyl group prefers to form an intramolecular hydrogen bond with an acetal oxygen, in contrast to the terminal hydroxyl group. Molecular mechanics and molecular dynamics on DBS dimers reveal that they are capable of forming hydrogen bonds and participating in π interactions, suggesting that the mechanism of nanofibrillar network formation may be complex, involving more than one type of physical interaction.

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

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.