The Influence of Chain-Ends on the Thermal and Rheological Properties of Some 40/60 PES/PEES Copolymers Lorenzo Abate, Ignazio Blanco, Gianluca Cicala, Giuseppe Recca, Andrea Scamporrino Dipartimento di Metodologie Fisiche e Chimiche per l’Ingegneria, University of Catania, Viale A. Doria, 6 95125 Catania, Italy Four random, differently ended (Cl, NH 2 , OH, and COO 2 ), polyethersulfone/polyetherethersulfone (PES/ PEES) copolymers were studied to investigate the influence of chain ends on thermal and rheological behaviors. The number average molar mass (M n  9500 gmol 21 ) and the PES/PEES ratio (40/60) of all copolymers investigated were checked by 1 H NMR spectra. Thermal degradations were carried out in the scanning mode and initial decomposition temperatures (T i ) and activation energy values of degradation (E a ) were obtained. Glass transition temperature (T g ) was determined by differential scanning calorimetry and complex viscosity (g*) by rheological measurements in isothermal heating conditions (T ¼ 2708C). All parame- ters determined were largely affected by copolymer chain ends and decreased according to the same order, OH > NH 2 > Cl > COO 2 . The results were discussed and interpreted. POLYM. ENG. SCI., 49:1477– 1483, 2009. ª 2009 Society of Plastics Engineers INTRODUCTION In recent years our group has been interested in the investigation of aromatic thermoplastic polymers contain- ing ether, ketone, and sulfone groups [1–9]. These poly- mers show usually good thermal and mechanical proper- ties, and it has been reported in literature that a wide spectrum of characteristics can be obtained by balancing opportunely various groups [10]. Moreover these poly- mers are of increasing technological importance; in partic- ular, polyethersulfones (PESs) are used as adhesives for metal-to-metal bonds [11], as membranes in the separa- tion of gases and solids from solutions [12] and as mem- branes for fuel cells [13]. More recently the use of PESs as toughening agents for brittle thermosetting resin has been attempted [14]. As we are interested in synthesizing new polymers for these purposes, for which not only low viscosity is requested as well as fairly good thermal stability and glass transition temperatures, we thus considered PES/ polyetherethersulfone (PES/PEES) copolymers, whose chains are more flexible than PES because of the presence of a larger number of ether links. We thus investigated in the past low molar mass Cl- and NH 2 -ended PES/ PEES copolymers, at various PES/PEES ratios, in order to compare their comprehensive thermal stabilities and rheological properties [8, 9]. Both thermal and rheological parameters were widely dependent on copolymer compo- sition in every case, but the trends observed for the two series of copolymers were different from each other. On the basis of the comprehensive picture of the results in Refs. 8 and 9, the 40/60 PES/PEES copolymer appeared to us as the most suitable for the present work, because its thermal and rheological parameters reasonably average among the needs of various uses. This choice was also in agreement with the literature report on the employment of 40/60 PES/PEES copolymer as toughening agent [15]. In this work, we thus studied some random differently (Cl, NH 2 , OH, and COO 2 ) ended PES/PEES copolymers, having the same PES/PEES ratio (40:60) as well as the same number average molar mass (M n  9500 gmol 21 ), and whose repeating units were the following A½AOAArASO 2 AArAA PES A½AOAArAOAArASO 2 AArAA PEES (where Ar is 1,4-substituted phenylene). We determined here the glass transition temperature (T g ) and the complex viscosity (g*) of the studied copolymers, as well as the characteristic parameters of decomposition, initial decomposition temperature (T i ) and apparent activa- tion energy (E a ) of degradation in both inert and oxidative environments, with the aim of investigating if and how much these parameters are affected by terminal groups. The dependence of the thermal, mechanical, and rheo- logical properties of polymers on the various functional Correspondence to: L. Abate; e-mail: labate@dmfci.unict.it Contract grant sponsor: The Italian M.I.U.R. DOI 10.1002/pen.21378 Published online in Wiley InterScience (www.interscience.wiley.com). V V C 2009 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2009