Energy transfer photocatalyst enabled by covalent organic framework induced reversible complexation-mediated polymerization under white LED light irradiation and the mechanism study

Abstract

Heterogeneous photocatalytic polymerization has emerged as a successful method for the development of greener reversible deactivation radical polymerization protocols. In this article, a halogen-free covalent organic framework (1,3,6,8-tetrakis(4-aminophenyl) pyrene-1,3,6,8-tetrakis(4-formylphenyl) pyrene-covalent organic framework [TAPPy-TFPPy-COF]) based on imine bonds was prepared, which mediated reversible complexation-mediated polymerization of methacrylates for the synthesis of various polymers with controllable molecular weight and relatively uniform distribution under white light-emitting diode light irradiation. TAPPy-TFPPy-COF absorbed the energy from photo and was transformed to excited state (COF•), and then the energy transfer occurred between COF• and initiator 2-iodo-2-methylpropionitrile (CP-I), which cleaved the carbon-iodine bond of CP-I to generate carbon radicals, thereby initiating the polymerization reaction. The density function theory calculation suggests that the coordination of iodine of CP-I with nitrogen on TAPPy-TFPPy-COF significant decrease the bond dissociation energy, making the polymerization more efficiency. The monomer conversion and reaction time showed a linear kinetic relationship of first order. The number average molecular weight of the obtained polymers increased along with the monomer conversion rate, and in good agreement with theoretical molecular weight, indicating a high frequency of the activation-deactivation cycle. The obtained polymer has high chain end fidelity, which can be used to synthesize various block copolymers. This work provided a new direction for the development of heterogeneous catalysts for reversible complexation-mediated polymerization.