Summary Low molar mass homopolymers, synthesized through free radical polymerization of acrylic acid under solvent control were reported. The polymers were characterized by FTIR, NMR, TGA, and GPC. The behavior as pour point improvers in biodiesel and blends biodiesel/diesel, were evaluated. By using 1000 ppm of the poly(tetradecyl acrylate) (A14) it was possible to decrease the pour point (PP) of neat biodiesel to −10°C, blend B5 to −39°C and blend B20 to −28°C, values below those reported in the literature. These results indicated that it would be possible to use higher amount of biodiesel in blends with diesel in regions where their use would not be feasible, mainly because of their poor flow properties.

Phenolic antioxidants have limited solubility in biodiesel, so this research developed new antioxidants by addition of hydroquinone and catechol on unsaturated fatty acid esters, which improved significantly the oxidative stability of rapeseed biodiesel. This new compound class is more soluble in biodiesel than hydroquinone and catechol, in same molar concentrations. The aging of biodiesel was studied using Metrohm model 743 Rancimat and PetroOxy devices and it was possible to observe an improvement on oxidation stability in both testing using these new antioxidants. Especially the additives 2MB3 and 4MB3 improved the induction period (IP) of rapeseed methyl ester (RME‐B100), from 4 to 63 and 65 h, respectively, with 30 mmol/kg of additives, while hydroquinone in comparison improves the stability to 25 h in the same molar concentration. This new class of antioxidants is promising to enhance oxidative stability of biodiesel, showing the capability of such additives to be commercialized for this purpose. Practical applications: Biodiesel is obtained by different raw materials, so the composition is different according to the source. The biodiesel with higher amounts of unsaturated fatty acids is more susceptible to oxidation than those with higher saturation. To solve problems caused by oxidative deterioration of biodiesel, this research aimed to synthesize a new class of antioxidants as an alternative for preventing and minimize oxidative damage of biofuels. Rapeseed biodiesel without any addition of additive was out of specification according to EN 14214, which regulates oxidative stability greater or equal to 8 h. The additives herein obtained improved significantly the oxidation stability for rapeseed biodiesel by more than 100%.