Influence of polar groups on the depressive effects of polymethacrylate polymers as cold flow improvers for diesel fuel

•A series of C14MC-BMI, C14MC-ACM, and C14MC-BMI-ACM were synthesized and used as cold flow improvers for diesel fuel.•C14MC-BMI-ACM in diesel exhibited better depressing effects than C14MC-BMI and C14MC-ACM.•The SP and CFPP of 1000 ppm C14MC-BMI-ACM (9:0.25:0.75) treated diesel decreased by 22 °C and 12 °C, respectively.•The depressive mechanisms of the C14MC-BMI-ACM in diesel were investigated. In this study, a series of polymethacrylate polymers of tetradecyl methacrylate-N-benzylmaleimide copolymers (C14MC-BMI), tetradecyl methacrylate-4-acryloylmorpholine copolymers (C14MC-ACM), and tetradecyl methacrylate-N-benzylmaleimide-4-acryloylmorpholine terpolymers (C14MC-BMI-ACM) were synthesized and characterized by 1H nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography. The influences of benzene rings and morpholine groups on the depressive effects of the polymers as cold flow improvers for diesel fuel were investigated. Results indicated that C14MC-BMI-ACM with benzene rings and morpholine groups leads to better cold flow properties in diesel in contrast to that of C14MC-BMI with benzene rings groups and C14MC-ACM with morpholine groups. Moreover, C14MC-BMI-ACM (9:0.25:0.75) at 1000 ppm showed the best depressing effect and decreased the solid point and cold filter plugging point of diesel by 22 °C and 12 °C, respectively. In addition, the depressive mechanism was studied using viscosity-temperature curves, differential scanning calorimeter, macrocrystal images, and polarizing optical microscope. The results revealed that compared with copolymers with only benzene rings or morpholine groups, terpolymers with benzene rings and morpholine groups delayed crystal precipitation, changed the number of crystals and liquid state, and modified crystal morphology, thereby significantly reducing the low-temperature viscosity and improving the cold flow properties of diesel fuel.