Bio-based polyimine vitrimer

This thesis is focused on the synthesis and the characterization of a polyimine based on vanillin derivative. As illustrated in Figure 1, vanillin reacted with 4,4'-oxydianiline (ODA) to produce the intermediate monomer, V-ODA (vanilline-4,4'-oxydianiline), which was subsequently used for polymer synthesis. In this reaction the ethanol was used as the solvent and the reaction take 6 hours at 80°C, finally the V-ODA separated by filtration and left to dry for 24 hours. The structure of V-ODA confirmed by 1H NMR and FTIR analyses. Thermogravimetri analysis (TGA) showed good thermal stability, and Differential Scanning Calorimetry (DSC) confirmed the absence of residual solvent. To synthesize Epoxy V-ODA (Figure 2) the synthesized V-ODA was reacted epichlorohydrin (ECH) at 110 °C and stirred for 30 minutes. To separate the desired epoxy the dichloromethane (DCM) and distilled water were added to form a two-phase system and extract water soluble impurities. Subsequently, to remove residual moisture anhydrous MgSO4 was used. Finally, hexene was introduced to aid to remove of remaining ECH before rotary evaporation. FTIR analysis of EV-ODA confirmed the successful attachment of the epoxy groups, as well as the disappearance of the hydroxyl and amine groups originally present in V-ODA. TGA revealed degradation temperature of 270°C, indicating high thermal stability. DSC analysis showed a broad endothermic peak around 137 °C, which is probably related post-curing of the material. In crosslinking step, EV-ODA was dissolved in dimethyl sulfoxide (DMSO) and Ytterbium (III) trifluoromethanesulfonate was added as the thermal initiator. Different amount of thermal initiator (3%wt, 4%wt and 5%wt) was added. The mixture was cured at 80 °C for 24 hours. FTIR analysis, which performed after the curing, confirmed the presence of imine groups and disappearance of epoxy ring in the polymer network; however, no significant differences were observed in the spectra of samples containing different amounts of thermal initiator. Therefore, the further test and analysis of this study was performed by using a 3%wt of the thermal initiator for each sample. Dynamic mechanical analysis (DMA), was initially performed over a temperature range of -15°C to 330°C. In the first trial, the storage modulus increased unexpectedly around 100°C, which might be due to post curing. In the second and third trials, the storage modulus decreased as the temperature increased. The glass transition temperature (Tg) increased from 247°C in the second trial to 298°C in the third trial which might be due to increasing crosslinking occurring during the heating cycles. Stress relaxation test was performed at 150°C on circular sample under 5%strain. The material showed significant stress relaxation after 1h, which indicate network rearrangement through imine bond exchange. Finally, reprocessability of material evaluate. Solvent free EV-ODA with 3%wt of thermal initiator hot pressed for 15 minutes at 150°C, which resulted in the formation of a very thin and homogenous film. After each tensile test, the brocken material hot pressed at 150°C , and in all four cycles, the resulting film was homogeneous. Despite the brittleness of film, it can withstand applying a load for a few moments before failure.