The reaction of styrene with a-methylstyrene has been studied over Y, Beta and ZSM-12 zeolites at 80-120 degrees C in the presence or absence of chlorobenzene. Homo- and codimers of styrene and alpha-methylstyrene were the main reaction products. The yield of dimers and their structure depends on zeolite type and the experimental conditions. Dimers were formed with greater selectively over zeolite HZSM-12 (S = 80-83%), for which the structural features promote the synthesis of linear compounds. In the presence of the zeolites HY and HBeta, cyclic homo- and codimers were the predominant products. The yield of dimers increases with increased reaction temperature and catalyst concentration, and in the presence of solvent. All zeolites investigated showed high codimerisation activity on styrene and alpha-methylstyrene at 120 degrees C. (C) 2011 Elsevier B.V. All rights reserved.