Hydrogen Bond Effects: A Strategy for Improving Controllability in Organocatalytic Photoinduced Controlled Radical Polymerization Targeting High Molecular Weight

Abstract

A highly efficacious photoinduced reversible complexation-mediated polymerization (photo-RCMP) system using amino alcohol N-oxide as the catalyst has been developed, allowing access to controlled high-molecular-weight polymers of different methacrylates (M n = 497–815 kg/mol, Đ < 1.5), which is very challenging for those known catalytic systems of photo-RCMPs and most organocatalytic photoinduced controlled radical polymerization as it demands higher controllability of catalysts. The monomers can be converted into the polymers nearly quantitatively under simulated or natural sunlight irradiation. Strong hydrogen bond effects are observed in this high-molecular-weight photo-RCMP, in terms of both monomer conversion and molecular weight controllability. The insights of the effects are revealed as the intramolecular hydrogen bond of the N-oxide catalyst modifies the electron density of N-oxide, and thereby facilitates the regeneration of the catalyst (activator) and release of I2 as a predominant effective regulator of radical concentration, by the studies of X-ray analysis, control experiments, density functional theory calculation, ultraviolet–vis absorption spectroscopy, etc.

Quantum chemical calculation driven insights into deep eutectic solvent‐accelerated photoinduced reversible complexation‐mediated polymerization

“…The photo-RCMP mechanisms generally include initiation, propagation, activation/deactivation equilibrium, and termination. 15,27,63 Detailed DES-accelerated photo-RCMP mechanism is described as follows (Scheme 1C): Initially, a complex (RI-DES) of alkyl iodide (RI) initiator and DES is formed. Subsequently, this complex is excited under irradiation, and the complex in the excited state dissociates to generate an alkyl radical (RÁ) and the complex ÁI-DES.…”

“…[1][2][3][4][5][6][7][8][9] In addition, Goto et al first develop reversible complexation-mediated polymerization (RCMP), 10 a mechanism in which the amine abstracts an iodine from Polymer-I to generate PolymerÁ and a complex of the iodine radical and amine, as shown in Scheme 1A. Recently, several researchers have been expanding the field of photo-RCMP, [11][12][13] including providing well-defined block copolymers, 14 obtaining controlled high molar mass polymers, 15 and employing novel covalent organic framework photocatalysts. 16 There are still drawbacks of photo-RCMP, for example, photo-RCMP in water or DMSO results in a slow polymerization rate due to low primary radicals concentration.…”

Enhancing Ultrasound-Assisted Iodine-Mediated Reversible-Deactivation Radical Polymerization by Piezoelectric Nanoparticles

“…This is probably due to the electron-withdrawing effects of fluorine atoms that promote the cleavage of the carbon−iodine bond. 43,49,50 GMA, BnMA, and MEMA also exhibited high monomer conversions with good control over the molecular weight.…”

“…A high conversion of 96% was then calculated for HFNBMA polymerization, yielding PHFNBMA with M n of 17000 Da and Đ of 1.08. This is probably due to the electron-withdrawing effects of fluorine atoms that promote the cleavage of the carbon–iodine bond. ,, GMA, BnMA, and MEMA also exhibited high monomer conversions with good control over the molecular weight.…”

“…Iodine-mediated reversible-deactivation radical polymerization uses alkyl iodides (R-I) as an initiator to establish equilibrium between active species (polymer • ) and dormant species (polymer-I). − It requires no conventional thermal initiator or expensive catalysts compared with other RDRP methods. Recently, photocontrolled RDRP was accomplished by Goto and others. − The development of a mechanochemical approach for the reversible deactivation process enables a sustainable implementation with broader applications. Herein, we report a novel mechanically controlled iodine-mediated reversible-deactivation radical polymerization (mechano-RDRP), using BTO as the mechanoredox catalyst and alkyl iodide as the initiator.…”