Fig. 3

Bottle-grade synthesis of PEF via ROP from cyclic oligomers. a Size exclusion chromatography (SEC) trace, showing that neat ring-opening polymerisation of 99% cyOEF without additional catalyst at 280 °C leads to relatively fast conversion of C3 and larger cycles to PEF, while C2 polymerisation is very slow and incomplete (black arrow). Simultaneously, the resulting heterogeneous system shows strong discolouration and molecular weight degradation, observable by the shift of the PEF peak to larger elution volumes over time. b Comparison of different ROP conditions to enable fast kinetics with short reaction times, all at 280 °C: neat (black squares), dry grinding of 0.1% (mol/mol) cyclic stannoxane initiator into cyOEF (blue diamonds), addition of fresh cyOEF into twice its mass of a reactive PEF melt at >90% conversion with the same initiator amount (purple triangles), 0.1% cyclic stannoxane added together with 33% (mass per mass cyOEF) tetraglyme as liquid inert plasticiser (red circles). The plasticiser alone without initiator (grey circles) increases kinetics to a smaller extent. c, d ROP using 0.1% (squares), 0.2% (diamonds) and 0.3% (triangles) cyclic stannoxane with 33% tetraglyme at 260 °C, resulting in full ( >96%) cyOEF conversions to high molecular weights exceeding the bottle-grade target of 30 kg mol⁻¹ within <20 min. e PEF from different routes: a high molecular weight product without undesired discolouration derived from ROP using 0.1% cyclic stannoxane initiator with 33% tetraglyme at 260 °C after 25 min (right), and a discoloured product from non-optimised ROP using 97% pure cyOEF at 280 °C with the same initiator for 60 min (middle), are compared with a typical industrial polycondensation PEF product (M_n = 15 kg mol⁻¹), which is similarly discoloured (left)