The isopropylation of diphenyl ether (PE) was examined over dealuminated H-mordenite (MOR) under 0.8 MPa of propene at 175-350 degrees C. 4,4'-Diisopropyldiphenyl ether (4,4'-DIPPE) was selectively formed at low and moderate reaction temperatures (175-250 degrees C). The selectivities for 4,4'-DIPPE decreased with increasing reaction temperature, and resulted in the formation of thermodynamically more stable 3,4'- and 3,3'-DIPPE at high temperatures (300-350 degrees C). The selectivities for DIPPE isomers in encapsulated products had similar features to the selectivities of bulk products. The shape-selective isopropylation of PE consecutively occurs at low and moderate reaction temperatures: 4-isopropyldiphenyl ether (4-IPPE) forms preferentially from PE, and then rapidly convert to 4,4'-DIPPE. However, the isomerization of 4,4'-DIPPE occurred on internal acidic sites in the channels as well as on external acidic sites at high temperatures. MOR channels were large enough for the isomerization of 4,4'-DIPPE at high temperatures because of the fluctuations of zeolite structure and organic molecules. These features of the isopropylation of PE were quite different from the isopropylation of biphenyl (BP), where no isomerization of 4,4'-diisopropylbiphenyl occurred inside the channels. These differences were due to the conformation of the transition states between PE and BP in MOR channels. Flexible conformation of 4,4'-DIPPE also enabled the isomerization inside the channels. (C) 2011 Elsevier B.V. All rights reserved.