A process for preparing a polymer having a 2,5-furandicarboxylate moiety within the polymer backbone and having a number average molecular weight of at least 10,000 (as determined by GPC based on polystyrene standards) includes a first step wherein a prepolymer is made having the 2,5-furandicarboxylate moiety within the polymer backbone, followed in a second step by a polycondensation reaction. In the first step a 2,5-furandicarboxylate ester is transesterified with a compound or mixture of compounds containing two or more hydroxyl groups, in the presence of a tin(IV) based transesterification catalyst. In the second step at reduced pressure and under melt conditions the prepolymer prepared in the first step is polycondensed in the presence of a tin (II) based polycondensation catalyst until the polymer is obtained. This polymer may then be subjected to Solid State Polycondensation. Polymers so produced may have a 2,5-furandicarboxylate moiety within the polymer backbone, and having a number average molecular weight of at least 20,000 (as determined by GPC based on styrene standards), and an absorbance as a 5 mg/mL solution in a dichloromethane:hexafluoroisopropanol 8:2 at 400 nm of below 0.05.