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abstract The thermal stability study of a conducting semi-IPN has been reported. The thermo-oxi-dation of poly(ethylene oxide) (PEO)/poly(3,4-ethylenedioxythiophene) (PEDOT)semi-Interpenetrating Polymer Network (semi-IPN) was studied at 80 C in open air. Thedegradation was followed by spectrophotometry in the visible and near infrared range,cyclic voltamperometry and thermogravimetric analysis. Fluorescence spectrophotometryallowed for the identification of OH by-product originated in the PEO network degradationby the use of a chemiluminescent probe, typically terephthalic acid. The formation ofhydroxyl radicals damaged the PEDOT chains as checked by infrared spectroscopy. Themechanism of degradation is further confirmed (i) by introducing a radical scavenger or(ii) by performing a thermal ageing under inert atmosphere; in both cases the semi-IPNlife-time is tremendously increased. 2008 Elsevier Ltd. All rights reserved. 1. IntroductionPoly(3,4-ethylenedioxythiophene) (PEDOT) is a veryattractive electronic conducting polymer (ECP) due to itsoptical and conductive properties and its high chemicaland thermal stability [1,2]. The range of its applicationsis very wide such as antistatic coating in photographicfilms [3], electrochromic devices [4,5], actuators [6,7].When associated with other polymers, PEDOT can be usedas injection layer in photovoltaic devices [8] or organiclight emitting diodes [9]. The main example is thePEDOT/PSS (poly(styrene sulfonate)) material which iscommercially available as a water colloidal dispersion.The PSS serves as counter-ion polyelectrolyte and allowsfor thin film preparation. Semi-interpenetrating polymernetworks (semi-IPNs) are a promising solution to associatetwo or more polymers and lead to new tailor-made mate-rials. They are defined as a combination of at least onecross-linked polymer and one linear polymer synthesizedin the presence of each other [10]. We have prepared freestanding films based on poly(ethylene oxide) (PEO)/PEDOTsemi-IPNs [11,12]. In this system, the PEDOT is embeddedwithin a PEO network and the resulting thin film (100–500