A series of poly(butylene 2,5-furandicarboxylate-co-terephthalate) copolyesters coPBFxTy covering the whole range of compositions has been prepared via ring opening polymerization (ROP). Cyclic oligomers of butylene 2,5-furandicarboxylate c(BF)n and butylene terephthalate c(BT)n, both mainly consisting of a mixture of dimer, trimer, and tetramer species, were synthesized by the high dilution condensation method. Random copolyesters with the targeted compositions and weight-average molecular weights within the 55¿000–80¿000 g·mol–1 range were obtained by ROP of c(BF)n/c(BT)n mixtures in periods of time much shorter than those required by melt polycondensation. The thermal properties of these copolyesters were consistent with their compositions and comparable to their isocompositional analogs obtained by polycondensation. A comparative kinetics study of the isothermal crystallization of the homopolyesters and copolyesters differing in composition revealed that the presence of the 2,5-furandicarboxylate units decreased the crystallization rate of PBT. Nevertheless, coPBFxTy copolyesters with moderate contents in BF units were still able to crystallized rapidly from the melt

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