Ethylene glycol-soluble Ti/Mg-citrate complex catalyst for synthesis of high intrinsic viscosity poly(ethylene terephthalate)

Antimony-free poly(ethylene terephthalate) (PET) has been synthesized through polycondensation of p-phthalic acid and ethylene glycol, and then subjected to a viscosity-increasing process by liquid-state polycondensation (LSP). For both of these processes, a novel environmentally benign ethylene glycol-soluble Ti/Mg bimetal (TM) catalyst has been used. The structure of the TM catalyst has been comprehensively characterized and its catalytic activity in the polycondensation reaction has been evaluated and compared with those of other titanium-based catalysts. The results reveal that the TM catalyst is a chelated complex with high catalytic activity for polycondensation to afford PET without significant side reactions. Indeed, the LSP process catalyzed by TM affords a PET product with high intrinsic viscosity suitable for industrial yarn production (1.08 dL/g) within 60 min, and that exhibits higher thermostability with increasing intrinsic viscosity. Finally, the kinetics of the TM-catalyzed polycondensation has been probed based on the variation of intrinsic viscosity with increasing polycondensation time.