Variations in the chemical characteristics of asphalt constituents and styrene-butadiene-styrene triblock copolymer (SOS) in the second type of polymer modified asphalt (MT) and during thermal degradation process are compared with those of the H type of polymer modified asphalt (MH) from the yields of four constituents in both MT and MH separated by solvent extraction, the average molecular weight of four constituents in MT and MH, the molecular weight distribution of SBS in MT and MH, physical properties (softening point and penetration), and concentration of radicals in MT and MH. As a result, the findings are as follows. During thermal degradation of both MT and MH, the decomposed SBS molecules combined with the asphalt constituents, which resulted the increases of asphaltene yields. Irrespective of term of thermal degradation within 10 days at 190 degrees C, the softening points and penetration values of MH were higher than those of MT. During thermal degradation process of MH, the content of radicals in MH was lower than that of MT due to incorporation of most of the asphalt constituents into the SOS molecules. As a result, in comparison with MT, decomposition of the SBS molecules and the increases of the yield and the average molecular weight of ASP were suppressed with the increase of term of thermal degradation of MH. (C) 2011 Elsevier B.V. All rights reserved.