Near Infrared Light Induced Radical Polymerization in Water

Abstract

We introduce a gold nanorod (AuNR) driven methodology to induce free radical polymerization in water with near infrared light (800 nm). The process exploits photothermal conversion in AuNR and subsequent heat transfer to a radical initiator (here azobisisobutyronitrile) for primary radical generation. A broad range of reaction conditions were investigated, demonstrating control over molecular weight and reaction conversion of dimethylacrylamide polymers, using nuclear magnetic resonance spectroscopy. We underpin our experimental data with finite element simulation of the spatio‐temporal temperature profile surrounding the AuNR directly after femtosecond laser pulse excitation. Critically, we evidence that polymerization can be induced through biological tissues given the enhanced penetration depth of the near infrared light. We submit that the presented initiation mechanism in aqueous systems holds promise for radical polymerization in biological environments, including cells.

Wavelength-resolved near infra-red light induced free-radical polymerization

“…For each sample, 150 μL aliquots were transferred from a stock solution of the initiator azobisisobutyronitrile (AIBN) in bulk DMA into a vial, adding 75 μL isopropanol, 75 μL AuNR in water and 10 μL 3-mercaptopropionic acid as chain transfer agent (CTA), such that each sample featured a concentration of 4.85 mol L −1 DMA, 3.53 mol L −1 isopropanol, 0.01 mol L −1 AIBN, 0.38 mol L −1 CTA and 75 μL of the AuNR solution. As highlighted in our previous publication introducing AuNR mediated polymerization, 41 the addition of a CTA is required to avoid high molecular weight chain growth resulting in precipitation of the polymer and thus not being soluble for further analysis. Moreover, as our previous report 41 has shown that the thermal activation of AIBN using AuNR photothermal converters seems not to be sensitive to oxygen quenching, the samples were irradiated without deoxygenation.…”

“…There exist several powerful techniques that make use of NIR light to induce polymerizations, most notably two-photon induced polymerization emitted from high intensity lasers or using NIR-light sensitive photothermal converters. [41][42][43][44][45][46][47][48][49][50][51][52][53] Previous studies have reported two-photon induced polymerizations in the MHz regime, 44,[47][48][49][50][51] while our team introduced an NIRlight two-photon pulsed laser polymerization. 53 However, since two-photon absorption processes require very high intensities as well as a coherent light source, this technique is limited to high energy light sources, such as lasers.…”

“…Alternatively, we successfully generated polymers using metal-based photothermal converters, irradiating a solution of monomer, a thermal initiator and gold nanorods (AuNRs) with a femtosecond (fs) NIR laser, making use of the plasmonic properties of AuNRs in generating a short high temperature envelope around each nanoparticle. 41 As the employed AuNR solutions feature a peak absorbance at close to 800 nm, we performed these first proofof-principle experiments with an 800 nm laser beam. However, as shown in a wide array of in-depth photochemical studies by our team using the so-called photochemical action plot technique using wavelength tuneable nanosecond (ns) pulsed laser systems, 38,[54][55][56][57] the peak reactivity of molecules is often shifted away from their peak absorbance.…”

Challenges and Opportunities in 3D Laser Printing Based on (1 + 1)-Photon Absorption

“…Finally, consider a photoresin in which a thermally activated radical initiator, e.g., an azo derivative, a (hydro)peroxide, or an alkoxyamine-based initiator, is combined with a heat generating dye, e.g., a cyanine borate 65 or a gold nanorod. 66 The local heating necessary to start the polymerization reaction is provided by the one-photon-excited dye molecules or gold nanorods. Thereby, even near-infrared light can be used to trigger the polymerization reaction.…”

Tailoring Polymerization Controllability and Dispersity Through a Photoswitchable Catalyst Strategy

“…Recently, switchable controlled radical polymerizations (CRPs) have brought new opportunities in polymer synthesis, in which dynamic equilibrium is regulated through the application or removal of an additional stimulus such as mechanical force, [1,2] light, [3][4][5][6][7] and electricity. [8,9] Notably, the majority of these CRPs are commonly utilized to develop polymerization systems exhibiting switchable (on/off) characteristics.…”