Fresh fracture surfaces formed by tensile failure of craze in molded polystyrene (PS) bars have been compared with the molded surfaces of the same bars, using an atomic force microscope with a thermal probe and operated in local thermal analysis. The results indicate that molecular weight is much higher in the interior of the sample than at the surface. No evidence was found for degradation of the PS chains via chain scission during crazing. Alternative explanations for the low-molecular weights at the molded surface are discussed. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2233-2237, 2010