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Asphalt-modification was studied using two different types of triblock copolymers both with star-like molecular architecture: poly(styrene-b-butadiene-b-styrene), SBS, and poly(styrene-b[(butadiene)1x-(ethylene-co-butylene)x]-b-styrene), SBEBS, to elucidate the effect of the molecular characteristics of the polymer and the polymer-content on the morphology and rheological behavior of polymer-modified asphalt, P-MA. The P-MAs were prepared using a hot mixing process and characterized using fluorescence microscopy and oscillatory shear flow measurements under linear viscoelastic conditions. Results revealed that the morphology of the polymer-rich phase and rheological behavior of the P-MA are dependent on the type and concentration of polymer: (i) P-MAs prepared with SBEBS exhibited higher dispersion in the asphalt matrix and were more elastic and less responsive toward frequency changes; (ii) P-MAs prepared with the polymer (SBS or SBEBS) of the larger molecular weight displayed higher elasticity; and (iii) the increase in the polymer concentration from 3 to 10 wt% resulted in the creation of P-MAs with higher elastic response. These results substantiate the importance of the molecular characteristics of the polymer in determining the properties of P-MAs, in particular composition of the elastomeric-b and molecular weight of these polymers, and the results are explained considering the molecular characteristics of these polymers and the polymer/asphalt interaction. POLYM. ENG. SCI., 53:2454–2464, 2013. © 2013 Society of Plastics Engineers