Visible Light‐Regulated Heterogeneous Catalytic PET‐RAFT by High Crystallinity Covalent Organic Framework

Abstract

Covalent organic frameworks (COFs) are a class of promising photocatalysts for conversing light energy into chemical energy. Based on the tunable building blocks, COFs can be well‐designed as photocatalyst for mediating reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. Herein, 1,3,6,8‐tetrakis(4‐formylphenyl)pyrene (TFPPy) and 2,2″‐bipyridine‐5,5″‐diamine (Bpy) are chosen to construct imine‐based TFPPy‐Bpy‐COFs for catalyzing RAFT polymerization of methacrylates under white light irradiation. The well‐defined polymers with precise molecular weight and narrow molecular weight distribution are obtained. The switch on/off light experiments suggest excellent temporal control toward RAFT polymerization system and the chain‐extension reaction indicates high chain‐end fidelity of macro‐initiators. Mechanism study clarifies that the electron transfer between excited state of TFPPy‐Bpy‐COFs and RAFT agent can form living radicals to mediate polymerization. This methodology provides a novel platform for reversible‐deactivation radical polymerization using COFs as heterogeneous catalysts.

Porphyrin-based donor–acceptor COFs as efficient and reusable photocatalysts for PET-RAFT polymerization under broad spectrum excitation

“…Hou and coworkers reported a COF-mediated photo-ATRP using copper catalysts. 34 The same group also demonstrated the use of fully-π conjugated COFs as PCs to mediate ATRP (with ppm-level copper) 35 and pyrene-based COFs for RAFT 36 under white-light irradiation. Cui and coworkers reported N , N -diaryl dihydrophenazine-based 2D and 3D COFs that promoted photoinduced radical ring-opening polymerization of vinylcyclopropanes, 37 achieving controlled molecular weight and low molecular weight dispersities.…”

Reusable polymer brush-based photocatalysts for PET-RAFT polymerization

“…12,29,[31][32][33] Heterogeneous photocatalysis is a viable alternative: [34][35][36][37][38][39][40][41] the ability to reuse catalysts for multiple reactions mitigates catalyst impurities, and improves both sustainability and cost effectiveness considering the often prohibitively expensive nature of some catalysts (e.g., Ir( ppy) 3 ). 12,18 Recent heterogeneous photocatalytic systems have been based on nanoparticles, [42][43][44][45][46][47][48][49][50][51] polymer networks, [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] metal oxides, [68][69][70][71][72] or catalytic (single chain nanoparticle) polymers. 73,74…”

“…, Ir(ppy) 3 ). 12,18 Recent heterogeneous photocatalytic systems have been based on nanoparticles, 42–51 polymer networks, 52–67 metal oxides, 68–72 or catalytic (single chain nanoparticle) polymers. 73,74 However, nanoparticles themselves strongly absorb visible light and reduce light penetration into the reaction mixture.…”

Influence of the Building Unit on Covalent Organic Frameworks in Mediating Photo‐induced Energy‐Transfer Reversible Complexation‐Mediated Radical Polymerization (PET‐RCMP)

“…Relying on the structural designability of building blocks and the stability of covalent connection mode in network, several of COF‐based PCs have been applied for inducing controlled radical polymerization and showed excellent controllability toward polymerization. For example, we have constructed pyrene‐based COF catalysts, TFPPy‐Td‐COF [19] and TFPPy‐Bpy‐COF, [20] for mediating ATRP and PET‐RAFT polymerization under visible light irradiation, and producing well‐defined polymers with precise molecular weight ( M n ) and narrow molecular weight distribution ( M w / M n ). Recently, Zhu and co‐workers reported porphyinic donor‐acceptor COFs for PET‐RAFT polymerization, indicating that the good catalytic polymerization performance of COF‐based catalysts [21] .…”