The present work focuses on the conception of bio-based epoxy resins arising from an increasing interest class of curing agents: the dicarboxylic acid. The hardener used was first synthesized from maleic anhydride and dipropylene glycol and then copolymerized with epoxidized linseed oil (ELO) to design resins from bio-resources. The anionic copolymerization between the two monomers has been highlighted by DSC while evolutions of chemical structures have been investigated by the corroboration of FT-IR and 2D NMR spectroscopies. DMA and DSC studies indicate that the copolymerization reaction is influenced by epoxy/dicarboxylic acid ratio and the presence of an initiator. Interestingly, the utilization of imidazole derivative as initiator provides selective reactions, which significantly increase the crosslink density and the α-relaxation temperature (Tα) of obtained networks. The resulting materials exhibit ductile and flexible behaviour with low Tα although keeping excellent thermal resistance (T10% > 315 °C).