Effective and facile solvent-free synthesis route to novel biobased monomers from vanillic acid: Structure–thermal property relationships of sustainable polyesters

Abstract

Solvent-free synthesis of monomers is one among the most promising ways to develop greener polymers that are both environmentally and economically acceptable, but it was described as one of the “grand challenges” facing chemists. As a contribution towards sustainable bioplastics development which has attracted great attention in materials science research, a truly efficient, practical, and more environmentally friendly solvent-free synthetic route was successfully applied herein to prepare three new fully biobased diol monomers derived from vanillic acid and aliphatic diols (ethylene glycol, 1,3-propanediol and 1,4-butanediol). Their chemical structures were confirmed in detail by 1H, 13C NMR and FTIR spectroscopies while their thermal properties were investigated by DSC and TGA. Results showed high melting points in the 121.8–142.3 °C range and no significant weight loss (Td, 5%) up to 243, 312 and 284 °C respectively for diols with 2, 3, and 4 methylene units. To prove their suitability in polymerization, melt polycondensation of prepared diols with three diacyl chlorides and also with dimethyl 2,5-furandicarboxylate were successfully carried out under catalyst-free conditions and using tetrabutyl titanate (TBT), respectively. The chemical structures of the novel series of polyesters were confirmed in detail by NMR and FTIR spectroscopies. The latter showed satisfactory intrinsic viscosity values in the 0.25–0.30 dL/g range and a wholly amorphous nature. All materials revealed high thermal stability with onset degradation temperatures Td, 5% ranging from 314 to 373 °C and a wide glass transition temperature (Tg) range oscillating from -2.8 to 69.5 °C. The innovative approach proposed herein for the first time, which involves the synthesis of sustainable monomers under solvent-free conditions, is fully aligned with one of the main principles of green chemistry.