Logic-Controlled Radical Polymerization with Heat and Light: Multiple-Stimuli Switching of Polymer Chain Growth via a Recyclable, Thermally Responsive Gel Photoredox Catalyst

Abstract

Strategies for switching polymerizations between "ON" and "OFF" states offer new possibilities for materials design and fabrication. While switching of controlled radical polymerization has been achieve using light, applied voltage, allosteric effects, chemical reagents, pH, and mechanical force, it is still challenging to introduce multiple external switches using the same catalyst to achieve logic gating of controlled polymerization reactions. Herein, we report an easy-to-synthesize thermally responsive organo-/hydro-gel that features covalently bound 10-phenylphenothiazine (PTH). With this "Gel-PTH", we demonstrate switching of controlled radical polymerization reactions using temperature "LOW"/"HIGH", light "ON"/"OFF", and catalyst presence "IN"/"OUT". Various iniferters/initiators and a wide range of monomers including acrylates, methacrylates, acrylamides, vinyl esters, and vinyl amides were polymerized by RAFT/iniferter and ATRP methods using Gel-PTH and a readily available compact fluorescent light (CFL) source. In all cases, polymer molar masses increased linearly with conversion, and narrow molar mass distributions were obtained. To further highlight the utility of Gel-PTH, we achieved "AND" gating of controlled radical polymerization wherein various combinations of three stimuli were required to induce polymer chain growth. Finally, block copolymer synthesis and catalyst recycling were demonstrated. Logic-controlled polymerization with Gel-PTH offers a straightforward approach to achieve multiplexed external switching of polymer chain growth using a single catalyst without the need for addition of exogenous reagents.

Seeing the Light: Advancing Materials Chemistry through Photopolymerization

“…For instance, our group recently demonstrated that Chl a could be used as a photocatalyst for polymerization and subsequently degraded by exposure to air under visible light, without affecting the chemical structure of the polymer products . Alternatively, photocatalysts for polymerization can be fixed to solid supports which simplifies the separation of the pure polymers and the photocatalyst after polymerization . Additionally, new chromophores that can attenuate far‐red and NIR light are required for future photochemical systems as longer wavelength irradiation is inherently safer, while also allowing increased depth penetration through non‐transparent materials compared to shorter wavelength irradiation.…”

Enhancing Temporal Control and Enabling Chain‐End Modification in Photoregulated Cationic Polymerizations by Using Iridium‐Based Catalysts

“…[1] Recently,c hemists have developed systems that gain spatiotemporal control over polymer chain growth with various external stimuli, adding to the repertoire of methods to control macromolecular structure. [2][3][4][5][6][7][8][9] These techniques have proven useful in av ariety of applications such as biological assays,p hotoresponsive materials,a nd surface patterning based on the ability to externally regulate chain-growth. Light is arguably one of the most powerful external stimuli used for polymerizations and new developments in this area will enable the synthesis of new functional materials.…”

Unraveling Photocatalytic Mechanism and Selectivity in PET‐RAFT Polymerization

“…[16,[24][25][26][27][28] As specific examples, considering the activity of PheoA (Figure 1a) and ZnTPP (Figure 1b) with respect to a set of six RAFT agents which comprises dithiobenzoates (4cyanopentanoic acid dithiobenzoate: CPADB, 2-cyano-2-propyl www.advancedsciencenews.com www.advtheorysimul.com Scheme 1. [16,[24][25][26][27][28] As specific examples, considering the activity of PheoA (Figure 1a) and ZnTPP (Figure 1b) with respect to a set of six RAFT agents which comprises dithiobenzoates (4cyanopentanoic acid dithiobenzoate: CPADB, 2-cyano-2-propyl www.advancedsciencenews.com www.advtheorysimul.com Scheme 1.…”