Ring opening copolymerization using simple Fe(III) complexes and metal- and halide-free organic catalysts

A comprehensive range of fourteen synthetically simple, air-stable and structurally diverse Fe(III) complexes, comprising of salalen, salen, salan and thiolen frameworks, were applied as catalysts to the ring opening copolymerization of phthalic anhydride (PA) and cyclohexene oxide (CHO) without the need for extra additives, such as co-catalyst, 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 weights, narrow dispersities and with high % ester linkages. Structure-activity-relationships have been investigated and discussed. The most interesting discovery was when performing ‘ligand control’ ROCOP experiments (highlighting the importance of such checks in catalysis) that 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 literature, examples tending to rely on two component systems with harsher, air-sensitive chemicals and these results provide hope that more reactive, effective organo-initiators 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 DSC analysis and, for the amorphous copolymers, the Tg values ranged by 35 °C from 100 °C to a respectable 135 °C.