Polyester copolymer

A polyester copolymer, having a number average molecular weight of equal to or more than 5000 grams/mole and having a glass transition temperature of less than 160° C., comprising the following repeating units:

• in the range from equal to or more than 45.0 mole % to equal to or less than 99.9 mole %, based on the total amount of moles of repeating units within the polyester copolymer, of one or more bicyclic diol-oxalate repeating units chosen from the group consisting of isosorbide-oxalate, isoidide-oxalate, isomannide-oxalate, 2,3:4,5-di-O-methylene-galactitol-oxalate and 2,4:3,5-di-O-methylene-D-mannitol-oxalate;
• in the range from equal to or more than 0.1 mole % to equal to or less than 50.0 mole %, based on the total amount of moles of repeating units within the polyester copolymer, of one or more linear C2-C12-diol oxalate repeating units;
• optionally in the range from equal to or more than 0.0 mole % to equal to or less than 5.0 mole %, based on the total amount of moles of repeating units within the polyester copolymer, of one or more additional repeating units;
• wherein the molar ratio of bicyclic diol-oxalate repeating units to linear C2-C12-diol oxalate repeating units is equal to or more than 1:1, more preferably equal to or more than 1.5:1.

A process for the production of a polyester copolymer, comprising polymerizing the following monomers:

• in the range from equal to or more than 25.0 mole % to equal to or less than 49.9 mole %, based on the total amount of moles of monomers, of one or more bicyclic diols chosen from the group consisting of isosorbide, isoidide, isomannide, 2,3:4,5-di-O-methylene-galactitol and 2,4:3,5-di-O-methylene-D-mannitol;
• in the range from equal to or more than 45.0 mole % to equal to or less than 50.0 mole %, based on the total amount of moles of monomers, of the one or more oxalic diesters having a chemical structure according to formula (VI):
• wherein R2 and R3 each independently are a C3-C20 alkyl group, a C2-C20 alkenyl group, a C4-C20 cycloalkyl group, a C4-C20 aryl group or a C5-C20 alkylaryl group;
• in the range from equal to or more than 0.1 mole % to equal to or less than 25.0 mole %, based on the total amount of moles of monomers, of one or more linear C2-C12 diols;
• and
• optionally equal to or more than 0.0 mole % to equal to or less than 5.0 mole %, based on the total amount of moles of monomers, of the one or more additional monomers.