Iodine and alkali metal alkoxides: a simple and versatile catalytic system for fully alternating polyester synthesis from phthalic anhydride and epoxides

A new environmentally benign synthesis of polyesters involves ring-opening alternating copolymerization (ROAC) of phthalic anhydride (PA) with various epoxides, utilizing molecular iodine and alkali metal alkoxides as novel dual catalytic systems under solvent-free conditions. With a suitable combination of iodine and alkali metal alkoxides, the reaction can be performed to a level of >99% conversion with good regioselectivity and respectable TOF values of 16 to 50 h(-1). We examined a series of commercial alkali metal alkoxides (MeOLi/Na/K, iPrOLi/Na/K, and tBuOLi/Na/K) in combination with molecular iodine for the copolymerization of epoxides with PA. The results indicate that the sodium and potassium alkoxides in combination with iodine showed higher activity. Particularly, I-2/tBuOK showed markedly higher activity exhibiting respectable TOF values in the range of 16 to 50 h(-1) towards the ROAC of PA with epoxides, which is comparable to the activity of metal-based complex catalysts. In addition, this methodology was employed for the copolymerization of PA with various epoxides such as CHO, PO, AGE, PGE, SO and tBGE. Each product exhibits a perfectly alternating sequence distribution, controlled molar mass (M-n up to 37.14 kDa), and low dispersity (D up to 1.04). Therefore, in the present work a novel and simple catalytic system was developed for regioselective fabrication of polyesters with diverse structures.

Automated summary

A new environmentally benign synthesis of polyesters has been developed using molecular iodine and alkali metal alkoxides as dual catalytic systems for the ring-opening alternating copolymerization of phthalic anhydride and various epoxides. The reaction showed high conversion, good regioselectivity, and respectable TOF values. This methodology allows the regioselective fabrication of polyesters with diverse structures.