This article covers the depolymerization of poly(ethylene terephthalate) (PET) under microwave irradiation in neutral water. The reaction was carried out in a sealed reaction vessel in which the pressure (or temperature) was controlled. The hydrolytic product contained terephthalic acid, ethylene glycol, and diethylene glycol characterized by IR spectrometry and gas chromatography. The undepolymerized PET was identified by gel permeation chromatography. Both the yield of terephthalic acid and the degree of PET depolymerization were seriously influenced by pressure (or temperature), the weight ratio of water to PET, and the reaction time. The applied irradiation power had little influence on the degree of PET depolymerization. With a pressure of 20 bar (temperature = 220degreesC), a reaction time of 90-120 min, and a weight ratio of water to PET of 10:1, the PET resin was depolymerized completely. The molecular weight and the molecular weight distribution indicated that the hydrolytic depolymerization of PET obeyed the regular chain-scission mechanism to some extent. (C) 2004 Wiley Periodicals, Inc.