Differential scanning calorimetry method was used for the study of thermal properties of terpolymers of styrene (ST) or methyl methacrylate (MMA) with dodecyl methacrylate and octadecyl methacrylate. Particularly, the interdependencies of the crystallinity content and composition of terpolymers were examined. The increase of the MMA or ST content in terpolymers resulted in the increased glass transition temperatures and decrease of the ratio of crystalline relative to amorphous phase (from 10% for xMMA = 10 mol% to 5.7% for xMMA = 30 mol%, and from 8.5% for xST = 16 mol% to 4% for xST = 40 mol%). These kinds of copolymers are commonly used as flow improvers at low temperatures for lubricating mineral oils; therefore a direct correlation between flow behavior of polymer solutions in mineral oil (pour point) and side-chain crystallinity of copolymers was examined. Thus, by increasing the proportion of crystalline phases, i.e. the long-chain alkyl methacrylates in copolymer, the pour point of oil solutions lowers. Thus, the solution of terpolymer with crystalline phase content of 4 mol% displays the pour point of −9°C while in those with crystalline phase content higher than 7 mol% pour point lowers below −30°C. POLYM. ENG. SCI., 53:2299–2307, 2013. © 2013 Society of Plastics Engineers