Chain extension of poly(ethylene terephthalate) (PET) with bisphenol-A dicyanate (BADCy) was studied using an internal mixer under reactive blending conditions. The reaction between PET and BADCy was confirmed by Fourier transform infrared (FUR) and chemical titration. With increasing amount of BADCy introduced, the modified PET gave rise to higher torque during stirred in an internal mixer, higher viscosity (eta'), and higher storage modulus (G'). Measurement of intrinsic viscosity showed that BADCy indeed extended the molecular weight of PET. DSC analysis represented that T, and T, of the modified PET were shifted to low temperatures. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2003-2008, 2010