Ring-Opening Copolymerization Using Simple Fe(III) Complexes and Metal- and Halide-Free Organic Catalysts

A comprehensive range of 14 synthetically simple, air-stable, and structurally diverse Fe (III) complexes, comprising salalen, salen, salan, and thiolen frameworks, were applied as catalysts to the ring-opening copolymerization (ROCOP) of phthalic anhydride (PA) and cyclohexene oxide (CHO) without the need for extra additives, such as co-catalysts, as part of a newly discovered unary system. Alternating poly (1, 2-cyclohexylene-1, 2-phthalate) poly (CHO-co-PA) was obtained with reasonable molecular weight, narrow dispersity, and high % ester linkage. Structure–activity relationships have been investigated and discussed. The most interesting discovery was that while performing “ligand control” ROCOP experiments (highlighting the importance of such checks in catalysis), all these organocatalysts outperformed their Lewis acidic Fe (III) analogues; these results are significant as a simplistic, metal- and halide-free, organocatalytic single-component approach to ROCOP was developed. There are few examples of organocatalysts in the literature, tending to rely on two component systems with harsher, air-sensitive chemicals, and these results provide hope that more reactive, effective systems are possible in an area very much in its infancy but will no doubt emerge and potentially prove vital to future sustainable polymerization research. Thermal properties were accessed via differential scanning calorimetry analysis, and for the amorphous copolymers, the Tg values ranged by 35 °C from 100 °C to a respectable 135 °C.