Ethyl octyl ether (EOE) can be obtained by the ethylation of 1-octanol by means of ethanol or diethyl carbonate over acidic ion-exchange resins. However, EOE formation has to compete with the less steric demanding formation of diethyl ether, by-product obtained from ethanol dehydration or diethyl carbonate decomposition. In the present work, the influence of the resin functionalization degree on EOE formation has been evaluated. A series of partially sulfonated resins (0.87-4.31 mmol H+/g) were prepared by the sulfonation of a macroreticular styrene-divinylbenzene copolymer. The catalysts were characterized, and subsequently, tested in a batch reactor (T = 150 degrees C, P = 25 bar). Amberlyst 15 and 46 were also tested for comparison purposes. Catalytic runs revealed that EOE formation occurred mainly in the firstly sulfonated domain of the polymer skeleton, the least crosslinked; while diethyl ether was formed in the whole polymer bead. Accordingly, the functionalization of the least accessible polymer domain, as a result of increasing the sulfonation temperature or by using a pre-swelling solvent, is not suitable to produce long chain ethers such as EOE; which are preferred as diesel fuels. (C) 2014 Elsevier Ltd. All rights reserved.