Cleaner synthesis and systematical characterization of sustainable poly(isosorbide-co-ethylene terephthalate) by environ-benign and highly active catalysts

Abstract

It remains a great challenge to cost-efficiently and cleanly synthesize sustainable polyesters based on both biomass-derived comonomers and biogenic catalysts because of the lack of clean, biogenic, and active catalysts so far. This work would like to address the tough problems of cleaner manufacturing and processing of the polyesters. We report the first example of the sustainable copolyesters from starch-based isosorbide/ethylene glycol and terephthalic acid by a highly active but environmentally benign Ti-Mg catalyst designed in our laboratory replacing current toxic catalysts. The optimal content of the Ti-Mg catalyst for productively synthesizing the copolyesters is down to 5 ppm that is just 1/30–1/75 content of traditional toxic catalysts including Sb2O3, GeO2, and pyridine reported heretofore. The copolyesters obtained by the Ti-Mg catalyst possess higher molecular weight up to Mn 25150, better performance, and are much more environmentally benign than most of similar copolyesters reported up to now. The copolyesters retain transparency owing to their irregular chain structure and random chain sequence and thus remain as a stable amorphous structure even after experiencing heating/cooling cycles. The Ti-Mg catalyst demonstrates 41–46 times higher catalytic activity than Sb2O3 catalyst and is active enough to catalyse the direct polycondensation between OH and COOH by eliminating water that is clearly distinguished from toxic methanol and corrosive HCl produced by polycondensation between OH and COOCH3/COCl catalyzed with toxic Sb2O3/pyridine catalysts, achieving cost-efficient and cleaner synthesis of the copolyesters without toxic residues. A systematic environmental analysis of the Ti-Mg catalyst, the copolyesters, raw materials and catalytic process, has been estimated, signifying that the Ti-Mg catalyst replacing current Sb2O3, GeO2, and pyridine accomplishes the cleaner production of most polyesters without toxic discharge or other harmful environmental impacts.