Commercial blow molding grade recycled high density polyethylene (R-HDPE) and blow molding grade virgin high density polyethylene (V-HDPE) were reactively extruded with various compositions (0.00-0.15% wt/wt) of different peroxides in a twin screw extruder. The aim was to produce the extended chain mechanism of a blow molding grade HDPE photopolymer-a polymer resin comprising a significant part of the post consumer recycled plastic stream in Australia. In shear rheological tests, the modified material exhibited an increase in viscoelastic properties and complex viscosity compared to unmodified counterparts. Higher extent of viscoelastic properties enhancement was observed with 1, 3 1, 4 BIS (tert-butylperoxyisopropyl) Benzene (OP2). This could be attributed to the higher degree of branching. The weight average molecular weight of the all modified materials and its molecular weight distribution (MWD) widened with peroxide modification. These results also support that formation of branching dominates the modification process at molecular level. Increase in branching index (g') with increase in peroxide composition also confirmed higher degree of branching. POLYM. ENG. SCI., 49:18061813, 2009. (C) 2009 Society of Plastics Engineers