The Use of the Straightforward Diels-Alder Reaction for the Preparation of Monomers From Tung Oil and Itaconic Acid-Derived Precursors: Synthesis, Characterization, and Screening of Their Polymerization Reactions

Abstract

The strict dependance of the polymer industry on petroleum-based chemicals has risen awareness on environmental safety and sustainability, motivating an at least partial shift towards the utilization of renewable platforms as alternative sources of raw materials. The strategy gains notoriety if one considers the preparation of novel macromolecules that cannot be obtained from petroleum using reasonable synthetic steps. In this work, tung oil and itaconic acid were used as bio-based feedstocks for the synthesis of novel polyfunctional monomers and polyesters. Primarily, methyl α-eleostearate, synthesized from tung oil and methanol, was applied as diene in a Diels-Alder reaction with dimethyl itaconate, leading to the formation of tri-ester monomers. A petroleum-based dienophile, n-butyl methacrylate, was also used to produce a bifunctional monomer. The synthesized monomers were characterized by FTIR/ATR, ¹H NMR and GC-MS, and then submitted to step-growth polymerizations with either glycerol or ethylene glycol, which allowed to synthesize novel linear and crosslinked bio-based polyesters. Spectroscopic analyses of the products suggested the success of the reactions, and TGA did not detect the presence of volatiles, with the materials being stable at temperatures up to 240 °C. DSC indicated a glass transition temperature at approximately 0 °C for one of the polymers, and an exothermic peak centered at about 140 °C, likely resulting from polymerization of the unsaturations in the polyesters. GPC indicated peaks with weight average molecular weights (\(\stackrel{-}{{M}_{w}}\)) of around 1400–2200 Da, suggesting the formation of oligomers. The results were encouraging and are expected to inspire new possibilities to produce bio-based polymeric materials.