Novel solventless purification of poly(propylene carbonate): Tailoring the composition and thermal properties of PPC

Poly(propylene carbonate), PPC, is produced via a catalytic copolymerization of CO2 and propylene oxide. The common side product propylene carbonate and catalyst residues are detrimental to the thermal and mechanical properties of the resulting PPC. Thus, efficient purification procedures are needed. PPC produced using zinc glutarate (ZnGA) catalyst was purified by a novel solid-liquid extraction using aqueous maleic acid. The resulting PPC exhibited a dramatically increased thermal stability as the onset of the degradation was increased by 85 °C compared to that of a crude PPC reference sample. It is suggested that metal-ion coordination between some in situ produced zinc species and the carbonyl moieties in the PPC backbone may explain this. The stiffness of the PPC increased by 75% when plasticizer side products were removed by the solid-liquid extraction. This novel purification method provides a sustainable alternative because only water and no organic solvent is used, and the method allows for the tailoring of the metal residues from the catalyst in the final polymer. The novel solid-liquid extraction procedure renders the PPC thermally stable at 200 °C for ca 60 min, thus expanding the processing window for PPC.