Cost-Effective Sustainable Synthesis of High-Performance High-Molecular-Weight Poly(trimethylene terephthalate) by Eco-Friendly and Highly Active Ti/Mg Catalysts

Efficient sustainable synthesis of high-performance poly(trimethylene terephthalate) (PTT) with simultaneously high molecular weight, narrow molecular weight distribution, and tiny cyclic dimer suitable for high end applications at low cost still faces challenges. Novel nontoxic and 1,3-propanediol-soluble Ti/Mg bimetal catalyst mainly based on biobased 1,3-propanodiol and food grade materials has been productively synthesized and also carefully characterized. The Ti/Mg catalyst was found to be exceptionally active catalysts for the polycondensation of terephthalic acid and 1,3-propanediol from a renewable resource capable of producing high-molecular-weight PTT as an environmentally friendly and recyclable material in both laboratory reactor and continuous pilot plant. The high-quality PTT samples with the highest number-average molecular weight up to 68 870 g/mol ever reported so far, the narrowest molecular weight distribution index down to 1.92, and the second lowest cyclic dimer content down to 2.21% simultaneously were synthesized for the first time at optimal Ti/Mg catalyst content and polycondensation temperature. Solid-phase polycondensation will result in even higher molecular weight up to 77 740 and even lower cyclic dimer content down to 1.92% at the same time. The kinetic analysis demonstrates that the polymerization by the Ti/Mg catalyst is faster and the degradation is slower than those by other catalysts reported. Pilot scale polymerization for productively synthesizing PTT was also carried out in a continuous plant, achieving cost-effective large-scale synthesis of PTT with the highest molecular weight and high performance. The properties of PTT obtained thus were superior to that of commercial grade. A systematical characterization signifies that the PTT catalyzed by Ti/Mg catalyst shows obvious characteristics including strong thermal-induced crystallinity, high glass transition temperature, elevated melting temperature, high melt viscosity, high storage modulus, high thermal stability, and excellent melt-spinnability.