Synthesis of polyesters mimicking polyethylene terephthalate and their thermal and mechanical properties

Abstract

Poly (dihydroferulic acid) (PHFA) from biorenewable vanillin was reported before as an alternative replacement of polyethylene terephthalate (PET). Thermal properties of PHFA were found to be very close to those of commercial polyethylene terephthalate (PET). However, PHFA was insoluble in common organic solvents, and it was difficult to measure molecular weight of the obtained polymer due to difficulty of performing gel permeation chromatography (GPC) analysis. In order to modulate the physical properties of PHFA, here we report a new kind of polyester synthesized from ethyl vanillin instead of vanillin as a starting material. Ethyl group on the monomer was found to disrupt the crystallinity, improve the thermal properties and increase the solubility of the obtained polymer. 3-(4-acetoxy)-3-ethoxyphenyl) propanoic acid (AEPPA) was obtained from the reaction between ethyl vanillin and acetic anhydride through Perkin reaction and subsequent hydrogenation. Polycondensation of AEPPA was achieved using zinc acetate catalyst and resulted in poly (3-(4-acetoxy)-3-ethoxyphenyl) propanoic acid) with 75% yield and high solubility in common organic solvents. Thermal transition temperatures of the obtained polymer are very close to those of commercial PET. Polycondensation was further extended to copolymerization of AEPPA and monomers derived from vanillin and syringaldehyde. Synthesized copolymers also showed higher solubility and tunable thermal properties compared to the PHFA from vanillin.