AbstractThis study describes low‐conversion terpolymerization kinetic investigations of methyl methacrylate/dodecyl methacrylate/octadecyl methacrylate (MMA/DDMA/ODMA) and styrene/dodecyl methacrylate/octadecyl methacrylate (ST/DDMA/ODMA) systems. Terpolymerizations were performed isothermally (70–105 °C), in 1 mol dm−3 xylene solutions, using 0.01 mol dm−3 of bifunctional peroxide initiator 1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane or monofunctional tert‐butylperoxy‐2‐ethylhexanoate. Synthesized terpolymers were characterized with respect to composition and molar mass distribution. Initial polymerization reaction rates as well as terpolymer average molar masses decreased with increasing MMA or ST content in the monomer mixture, for both initiators and all investigated temperatures. Overall reaction rates were found to be significantly larger for the MMA/DDMA/ODMA system. In the MMA/DDMA/ODMA system, experimental terpolymer compositions were found to be similar to the initial monomer feed compositions—all the experimental monomer feed mixtures were close to the azeotropic composition. The Alfrey–Goldfinger terpolymerization equation was successfully used for the description of MMA/DDMA/ODMA terpolymerization kinetics, where the existence of the true azeotropic ternary point was established. The same equation did not perform as well for the ST/DDMA/ODMA terpolymerization system. Copyright © 2006 Society of Chemical Industry