Dimethyl 2-Methylterephthalate: A Versatile Building Block in Polyester Synthesis with Intriguing Gas Barrier Properties

This article describes the potential of using a "methyl-branched dimethyl terephthalate," i.e., dimethyl 2-methylterephthalate, in the synthesis of polyalkylene methyl terephthalate. By employing linear diols with varying carbon chain lengths, three different polyesters were synthesized via the classical melt-polycondensation procedure. All polymers exhibited high molecular weights and thermal stabilities similar to poly(ethylene-terephthalate) (PET). The newly synthesized polyesters, poly(ethylene-methyl-terephthalate) (PEmT) and poly(propylene-methyl-terephthalate) (PPmT), are obtained as amorphous materials, whereas poly(butylene-methyl-terephthalate) (PBmT) is semicrystalline. In comparison to commercial PET, the branched methyl group is attributed with superior gas barrier properties as well as very similar tensile strength and elongation at break for PEmT. The combination of comparable mechanical properties and enhanced gas barrier performance of PEmT suggests substantial potential to replace petroleum-based polyesters in many application areas.