Free‐radical polymerization upon near‐infrared light irradiation, merging photochemical and photothermal initiating methods

Abstract

Polymerization of (meth)acrylate resins upon nearinfrared (NIR) light remains a huge challenge. In this study, a new photoinduced method of polymerization of methacrylic monomers is presented, originally merging a photochemical and a photothermal pathway. A four-component system is proposed comprising an NIR dye combined with an iodonium salt, a phosphine, and a thermal initiator. A selection of dyes is suggested regarding electron transfer properties and/or light-toheat conversion abilities. Several thermal initiators are studied: an alkoxyamine (BlocBuilder MA), an azo derivative, and a peroxide. For the first time, an NIR absorbing dye is used in photopolymerization using both its capacities of light-to-heat conversion and its ability to initiate an electron transfer reaction. Three wavelengths of irradiation will be presented here: 785, 940, and 1064 nm. These long wavelengths are challenging because the energy of photons is extremely low but these wavelengths offer significant advantages in term of light penetration (e.g., for the access to composites through photopolymerization processes). The different systems presented here exhibit high and rapid conversions of methacrylate functions. The underlying chemical mechanism will be fully depicted by real-time Fourier transform infrared spectroscopy and thermal imaging measurements.Additional supporting information may be found in the online version of this article.

New Donor-Acceptor Stenhouse Adducts as Visible and Near Infrared Light Polymerization Photoinitiators

“…This shows that only the combined mode leads to a high yield in initiating radicals to overcome the oxygen inhibition. Such a behavior has been found in [64] for other dyes. In this work, only dyes active in this combined mode are efficient.…”

“…This blend has been prepared with 33.3 wt% of (hydroxypropyl)methacrylate (HPMA), 33.3 wt% of 1,4-butanediol dimethacrylate (1,4-BDMA) and 33.3 wt% of a urethane dimethacrylate monomer (UDMA), obtained from Sigma Aldrich (St. Louis, MO, USA). This benchmark blend has an adapted viscosity for polymerization under air [44,[61][62][63][64]. It has to be noticed that the 13 DASA dyes DASA1-DASA13 examined in this work are Stenhouse adducts meaning that these structures can discolor upon irradiation in the visible range.…”

“…The peak followed by Real Time Fourier Transform Infrared (RT-FTIR) spectroscopy (using a Jasco 4600 instrument, Jasco, Tokyo, Japan) is located at 6100-6220 cm −1 as presented in [37]; this peak corresponds to the first overtone of the C-H vibrations of the =CH 2 acrylate group. The NIR photoinitiating systems are composed of (NIR) dyes (DASA1-DASA13, PP25 or PP26) combined with an iodonium salt (Ar 2 I + .PF 6 ), a phosphine (4-dppba) and a thermal initiator (here BlocBuilder MA) (see Figure 7) to take advantage of the photoinitiating system (NIR dye/iodonium/phosphine) associated with the photothermal system (NIR dye/BlocBuilder MA) as presented for other NIR dyes in [64].…”

In situpolymerization process: an essential design tool for lithium polymer batteries

“…A free-radical polymerization is usually carried out using energy sources such as heat, UV light, visible light, gamma rays, microwave, infrared (IR) rays, and so on. 344,371 Using these techniques, various types of linear, branched, homo-polymers, copolymers, and cross-linked systems can be produced within few seconds to few hours. A typical free-radical thermal/photopolymerization reaction needs monomers or oligomers having an unsaturated functional group (vinyl or allyl) and an initiator.…”

Metalated porphyrins as versatile visible light and NIR photoinitiators of polymerization

“…Considering that the light penetration is the key-parameter to polymerize thick samples, recently, NIR light photopolymerization has been the focus of numerous research efforts and structures such as squaraines, phthalocyanines, cyanines, Bodipys or negative photochroms such as the Donor-Acceptor Stenhouse Adducts (DASA) have been examined for this purpose. [12][13][14][15][16][17][18][19][20][21] However, there is a constant strive to find new structures activable in the near infrared region. At present, porphyrins have only been scarcely for NIR light polymerization despites their appropriate absorptions.…”