Free Radical Polymerization Initiated and Controlled by Visible Light Photocatalysis at Ambient Temperature

Abstract

A new method of free radical polymerization is developed on the basis of visible light photocatalysis using Ru(bpy)3Cl2 that initiates and controls the polymerization at ambient temperature. The α-haloester and benzylic halide act as radical initiators that can be activated through the Ru(bpy)3 + photoredox cycle under visible light irradiation. Successful free radical polymerizations of various methacrylates were realized using a Xe arc lamp as well as a household fluorescent lamp as light source. The polymerization is initiated with light on and immediately terminated upon turning the light off. In addition, the molecular weight of polymer can be varied by changing the ratio of monomer and initiator. The present photocatalytic method has merits of the mild reaction conditions with weak light irradiation, ambient temperature, and lower catalyst loading, which could be an alternative to the traditional thermal or photo-based free radical initiation methods. It is also advantageous over other photopolymerization methods in that the radical initiator is separated from the photosensitizer.

Synthesis and characterization of latex nanoparticles using a visible-light photoinitiating system in reverse micelles

“…However, the use of radiation in the visible region presents several advantages compared to thermal or UV initiation of polymerization [11][12][13][14]. These advantages are, for example, (i) lower cost by making use of visible photons emitted by the Hg lamps which are lost when the light is only absorbed by a UV photoinitiator (PI), (ii) a better matching of the emission spectrum of the light source and the absorption spectrum of the PI when laser lights are used, (iii) higher penetration ability of the visible radiation, and (iv) the opportunity to use sunlight for the curing of outdoor coatings.…”

Visible light photopolymerization in BHDC reverse micelles. Laser flash photolysis study of the photoinitiating mechanism

“…The use of radiation in the visible region presents several advantages compared to thermal or UV initiation of polymerization [4,5]. These advantages are, for example: (i) lower cost by making use of visible photons emitted by the Hg lamps which are lost when the light is only absorbed by a UV photoinitiator (PI), (ii) a better matching of the emission spectrum of the light source and the absorption spectrum of the PI when laser lights are used, (iii) higher penetration ability of the visible radiation, and (iv) the opportunity to use sunlight for the curing of outdoor coatings.…”

Photopolymerization Reactions: On the Way to a Green and Sustainable Chemistry

“…The current efforts result in an amazing series of proposals of new PISs . For example, we have recently introduced PISs ( [99][100][101][102][103][104][105][106][107]) exhibiting really novel absorption properties (red-shift absorptions, multicolor absorptions, enhanced molar extinction coefficients, ε): e.g., colored substituted or functionalized ketones [60], modified organometallic derivatives [70][71][72][108][109][110][111][112][113][114][115][116][117] (ruthenium-, iridium-, platinum-, zirconium-and zinc-based complexes, titanocene derivatives…), various series of dye-based skeletons [61][62][63][65][66][67][68][74][75][76] (e.g., phenylenediamine, polystilbene, polyazine, violanthrone, acridinedione, 2,7-di-tert-butyldimethyldihydropyrene, bodipy, boranyl, thiophene, perylene bis-dicarboximide, hydrocarbons, pyrromethene, pyridinium salt…), di-and tri-functional architectures of photo initiators [64], light harvesting compounds [57,58] (where a strong molecular orbital coupling occurs, leading to ε huge values) and push-pull and multicolor photoinitiators (novel chromophores; donor--acceptor arrangements; unusual broad absorptions from the blue to the red wavelengths…).…”

“…The further introduction of the silyl chemistry into photoredox cycles (as those known in organic synthesis purposes using photocatalysts (PC) [108][109][110][111][112][113][114][115][116][117]) has recently led to interesting possibilities of FRP and FRPCP reactions under soft conditions in aerated media [75,76,[105][106][107]. Novel PIs working as PCs through an oxidation cycle (metal complexes or organic metal-free compounds) in combination with a silane and an iodonium salt have been designed (22)(23)(24)(25); they allow successful excitations of cationic or radical matrices up to 635 nm under air.…”