PET polymer with an anti-crystallization comonomer that can be bio-sourced

A method to prepare a PET polymer comprising:

• diacid units derived from diacid compounds, said diacid units comprising:
• a) from 96.14 mol % to 97.15 mol % of said diacid units being terephthalic acid (TA) units or an ester thereof, and
• b) from 2.85 mol % to 3.86 mol % of said diacid units being 2,5-furandicarboxylic acid (2,5-FDCA) units or an ester thereof, based on 100 mol % of all diacid units, and
• diol units derived from diol compound(s), said diol units comprising monoethylene glycol units in an amount of at least 95.00 mol % of the diol units and optionally diethylene glycol units in an amount of less than 5.00 mol % of the diol units, based on 100 mol % of all diol units, comprising copolymerizing a mixture of:
• the diacid compounds comprising terephthalic acid (TA) or an ester thereof, and 2,5-furandicarboxylic acid (2,5-FDCA) or an ester thereof, and
• the diol compound(s), wherein the diol compound(s) comprise at least 95.00 mol % of monoethylene glycol of said diol compound(s) based on 100 mol % of all diol compound(s),
• wherein copolymerizing comprises a first step of melt polymerization and a second step of solid state polymerization,
• wherein the melt polymerization comprises a first sub-step of esterification or transesterification and a second sub-step of polycondensation,
• wherein the polycondensation is performed at a temperature of 285° C. in the presence of Sb2O3 as a catalyst.