Efficient preparation of cyclic polymers via pre-stacking of photo-cycloaddition capable end groups and a continuous-flow technique

Abstract

Cyclic polymers have recently attracted more and more attention due to their unique structures and performance, but their synthesis still presents great challenges. The commonly used ring-closure strategy to synthesize them mainly has the problem of low efficiency caused by the extremely dilute reaction concentrations, which limits its further in-depth study and widespread application. In this work, an efficient polymer cyclization process was developed to produce a series of well-defined monocyclic polystyrene, polycaprolactone, and polyethylene oxide polymers by pre-stacking of styrylpyrene (SP) groups at the end of linear precursors and a photo-cycloaddition reaction. Due to the pre-stacking of the SP groups, cyclization could occur at relatively high concentrations (∼10⁻⁴ M), higher than that of the general ring-closure strategy. Assisted by continuous-flow technology, the efficiency of cyclization could be further improved and photodamage could be reduced. The maximum production rate for preparing monocyclic polymers is about 54 mg h⁻¹, which is at least 7 times faster than that of other traditional ring-closure methods. This method is expected to make large-scale continuous preparation of cyclic polymers possible.