The effect of processing history in a single-screw extruder on molecular characteristics was studied by employing commercially available low-density polyethylene with no additives. Generation of long-chain branch, which is responsible for the neck-in phenomenon and draw resonance, is indicated by nonlinear viscoelastic properties of the extruded samples. Consequently, the processed samples show higher level of elastic property than the original pellet. However, thermal analysis revealed that there is no change in the distribution of short-chain branch. Moreover, both chain scission and cross-linking take place, and the chain scission is predominant above 320 degrees C. Furthermore, processing history at low temperature depresses the melt elastic nature, although primary molecular structure is unchanged. This would be attributed to shear modification phenomenon. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1462-1470, 2009