MICROSTRUCTURE OF TRIBLOCK COPOLYMERS IN ASPHALT OLIGOMERS

A model asphalt has been separated into two parts, asphaltene and malt ene, through solvent extraction by n-heptane. The interactions of asph altene and maltene with the triblock copolymer poly(styrene-b-(ethylen e-co-butylene)-b-styrene) (SEBS) were investigated by transmission ele ctron microscopy(TEM), small-angle X-ray scattering (SAXS), dynamic me chanical analysis (DMA), and differential scanning calorimetry (DSC). Asphaltene was found to be essentially immiscible with both blocks of SEBS, while maltene was miscible with SEBS. An unusual sequence of mor phological transformations of SEBS microstructure with respect to the addition of maltene was observed. The morphology transformed from hexa gonal cylinder, to perforated layers, to lamellae and then back to the original hexagonal cylinder. The observed transformation reflects a l imited solubility for both S and EB domains: at lower concentration ma ltene is a preferential additive for S domains, while increasing conce ntration the swelling of EB-rich microdomains by maltene becomes signi ficant. The basic understanding of the interactions of the components of asphalt with SEBS gives a simple path to characterize and predict t he microstructure of triblock copolymers in asphalt oligomers. (C) 199 7 John Wiley & Sons, Inc.