Free Radical Polymerization Of Acrylates Research Articles

Improved Approach for ab Initio Calculations of Rate Coefficients for Secondary Reactions in Acrylate Free-Radical Polymerization.

Secondary reactions in radical polymerization pose a challenge when creating kinetic models for predicting polymer structures. Despite the high impact of these reactions in the polymer structure, their effects are difficult to isolate and measure to produce kinetic data. To this end, we used solvation-corrected M06-2X/6-311+G(d,p) ab initio calculations to predict a complete and consistent data set of intrinsic rate coefficients of the secondary reactions in acrylate radical polymerization, including backbiting, β-scission, radical migration, macromonomer propagation, mid-chain radical propagation, chain transfer to monomer and chain transfer to polymer. Two new approaches towards computationally predicting rate coefficients for secondary reactions are proposed: (i) explicit accounting for all possible enantiomers for reactions involving optically active centers; (ii) imposing reduced flexibility if the reaction center is in the middle of the polymer chain. The accuracy and reliability of the ab initio predictions were benchmarked against experimental data via kinetic Monte Carlo simulations under three sufficiently different experimental conditions: a high-frequency modulated polymerization process in the transient regime, a low-frequency modulated process in the sliding regime at both low and high temperatures and a degradation process in the absence of free monomers. The complete and consistent ab initio data set compiled in this work predicts a good agreement when benchmarked via kMC simulations against experimental data, which is a technique never used before for computational chemistry. The simulation results show that these two newly proposed approaches are promising for bridging the gap between experimental and computational chemistry methods in polymer reaction engineering.

Photoinitiation Mechanisms of Novel Phenothiazine‐Based Oxime and Oxime Esters Acting as Visible Light Sensitive Type I and Multicomponent Photoinitiators

AbstractIn this work, three new photoinitiators, based on the phenothiazine scaffold as a chromophore and potentially bearing the oxime ester functionality as an initiating group are designed and synthesized for the free radical polymerization of acrylates, the cationic polymerization of epoxides, and the formation of interpenetrated polymer networks upon irradiation with a light emitting diode emitting at 405 nm. These phenothiazine‐based oxime and oxime esters revealed impressive photoinitiation ability manifested by excellent polymerization rates and high final reactive function conversions. Significantly, they can be used as both; one‐component (Type I) and two‐component photoinitiating systems. Photoinitiation mechanisms through which reactive species are produced are investigated by means of different complementary techniques including real‐time Fourier transform infrared spectroscopy, UV–visible absorption spectroscopy, electron spin resonance spectroscopy, fluorescence (steady state and time resolved), cyclic voltammetry, and molecular modeling calculations. Thermal initiation behavior of the different oxime esters is also studied by using differential scanning calorimetry, highlighting their dual thermal/photochemical initiation ability. Finally, 3D printed objects are successfully fabricated by conducting both direct laser writing and 3D printing experiments.

Chemical engineering around the 5,12-dihydroindolo[3,2-a]carbazole scaffold: Fine tuning of the optical properties of visible light photoinitiators of polymerization

5,12-Dihydroindolo[3,2-a]carbazole is a promising scaffold for the design of visible light photoinitiators of polymerization due to the simultaneous presence of two carbazole moieties that can be differently functionalized. Notably, redshift of the absorption spectra can be facilely obtained by nitration of one of the two carbazoles, the second carbazole group being functionalized with various groups. Dinitration of 5,12-dihydroindolo[3,2-a]carbazole is another efficient approach for designing dyes with strong absorptions extending over the visible range. In this work, a series of 36 compounds never reported in the literature and differing by the substitution pattern have been designed and synthesized. Notably, the possibility to design push–pull dyes by Knoevenagel and Claisen Schmidt reactions, to introduce electroactive groups such as thiophene by Suzuki cross-coupling reactions or to design water soluble chromophore has been explored. To evidence the interest of these structures, photopolymerization experiments have been carried out at 405 nm and the polymerization of acrylates has been examined in thick and thin films. To support the polymerization efficiency, mechanisms involved in the free radical polymerization of acrylates have been established by the combination of various techniques including UV–visible absorption and fluorescence spectroscopy, cyclic voltammetry and photolysis experiments.

Novel chalcone-based phenothiazine derivative photoinitiators for visible light induced photopolymerization with photobleaching and good biocompatibility

Two novel visible light photoinitiators 4-(10-methyl-10H-phenothiazin-3-yl) but-3-en-2-one (PBO) and (1E,4E)-1,5-bis(10-methyl-10H-phenothiazin-3-yl)-1,4-pentadien-3-one (BMPPO) were successfully designed and synthesized. PBO and BMPPO have broad absorption range from 350 to 500 nm with the maximum absorption wavelength at 400 nm and 440 nm respectively. Three-component photoinitiating system of BMPPO/iodonium/amine was developed for free radical polymerization of acrylates. The results demonstrated that the photoinitiating system displayed rapid polymerization and high final vinyl group conversions under the irradiation of UV-LED (365 nm), blue LED (440) nm and solar light resource. Moreover, photopolymerization kinetics was studied by real-time FT-IR spectrum, the double band conversion was achieved up to 90% for BMPPO. The photocuring mechanism was identified via steady state photolysis and electron spin resonance spin-trapping experiments. The possible photoinduced mechanism of PBO and BMPPO in the presence of a co-initiator occurred through electron transfer. In addition, BMPPO possesses rapid photobleaching and good biocompatibility performance tested by photoinduced degradation and cytotoxicity experiments respectively, which exhibited that BMPPO has potential for light-color coatings and food packaging field.

Liquid Crystalline Elastomers Based on Click Chemistry.

Liquid crystalline elastomers (LCEs) have emerged as an important class of functional materials that are suitable for a wide range of applications, such as sensors, actuators, and soft robotics. The unique properties of LCEs originate from the combination between liquid crystal and elastomeric network. The control of macroscopic liquid crystalline orientation and network structure is crucial to realizing the useful functionalities of LCEs. A variety of chemistries have been developed to fabricate LCEs, including hydrosilylation, free radical polymerization of acrylate, and polyaddition of epoxy and carboxylic acid. Over the past few years, the use of click chemistry has become a more robust and energy-efficient way to construct LCEs with desired structures. This article provides an overview of emerging LCEs based on click chemistries, including aza-Michael addition between amine and acrylate, radical-mediated thiol-ene and thiol-yne reactions, base-catalyzed thiol-acrylate and thiol-epoxy reactions, copper-catalyzed azide-alkyne cycloaddition, and Diels-Alder cycloaddition. The similarities and differences of these reactions are discussed, with particular attention focused on the strengths and limitations of each reaction for the preparation of LCEs with controlled structures and orientations. The compatibility of these reactions with the traditional and emerging processing techniques, such as surface alignment and additive manufacturing, are surveyed. Finally, the challenges and opportunities of using click chemistry for the design of LCEs with advanced functionalities and applications are discussed.

Sunlight Induced Polymerization Photoinitiated by Novel Push–Pull Dyes: Indane‐1,3‐Dione, 1H‐Cyclopenta[b]Naphthalene‐1,3(2H)‐Dione and 4‐Dimethoxyphenyl‐1‐Allylidene Derivatives

AbstractThe free radical polymerization of acrylates photo‐initiated by push–pull dye‐based photoinitiating systems (PISs) is widely investigated in previous works. As a supplementary investigation on push–pull dyes, here in this article, 25 push–pull structures comprising electron acceptors derived from indane‐1,3‐dione and 1H‐cyclopenta[b]naphthalene‐1,3(2H)‐dione (series 1) and 4‐dimethoxyphenyl‐1‐allylidene moieties (series 2) and various electron donors are synthesized and examined as innovative structures for photoinitiation. Among the two series of dyes examined in this work and by monitoring the polymerization processes by RT‐FTIR measurements, four dyes are determined as exhibiting excellent photoinitiation performances and these dyes are selected to perform further studies concerning the chemical mechanisms occurring inside the three‐component PISs, for example, steady state photolysis, fluorescence quenching measurements, and cyclic voltammetry. Markedly, their reactivity is also proved by photoinitiation performance upon sunlight. These results prompt us to develop high performance push–pull dyes as photosensitizers and sunlight can be used as a mild and ecofriendly light source, which can advantageously replace LEDs for the free radical photopolymerization in the future. Finally, the formation of 3D patterns with an excellent gradient of resolution is successfully achieved by the direct laser write (DLW) with/without silica fillers.

The new LED-Sensitive photoinitiators of Polymerization: Copper complexes in free radical and cationic photoinitiating systems and application in 3D printing

A ligand (A1) and four copper complexes (Cu1, Cu2, Cu3 and Cu4) were examined as photosensitizers in various photoinitiating systems (PISs). Interestingly, excellent photochemical reactivities were determined with the different compounds. Especially, notable photoinitiation abilities were determined upon exposure to LED@405 nm during the free radical polymerization of acrylates and the cationic polymerization of epoxides when combined with an iodonium salt and an amine. With regards to their remarkable reactivities, the different photoinitiating systems were applied to 3D printing experiments. By combining steady state photolysis and electron spin resonance spin trapping, the chemical mechanism supporting the polymerization processes could be fully detailed and proved. Among all PISs studied, the three-component PISs furnished the best monomer conversions during the free radical polymerization of trimethylolpropane triacrylate (TMPTA) and the cationic polymerization of (3,4-epoxycyclohexane)methyl 3,4-epoxycyclohexylcarboxylate (EPOX) monomers. The conversion process was monitored by real-time Fourier transform infrared spectroscopy (RT-FTIR). Three-component PISs based on A1, Cu1 and Cu2 showed better performances than those based on Cu3, Cu4 and the different two-component PIS (comprising only the iodonium salt or the amine) in FRP experiments. Based on the outstanding photoinitiation abilities of A1 and Cu1 with both TMPTA and EPOX, smooth and regular 3D patterns could be obtained by direct laser write experiments by generating interpenetrating polymer networks (IPN) with the blend of these two monomers.

5,12-Dihydroindolo[3,2-a]carbazole: A promising scaffold for the design of visible light photoinitiators of polymerization

5,12-Dihydroindolo[3,2-a]carbazole is a polycyclic structure combining in its scaffold two carbazole moieties sharing a fused aromatic ring. Since the pioneering works reported in 2019 on this structure concerning the substitution of the two carbazoles by similar functional groups, no recent investigation has been devoted to asymmetrize the substitution of the two carbazoles. In this work, a series of 13 compounds based on the 5,12-dihydroindolo[3,2-a]carbazole scaffold is presented. By carefully controlling the reaction conditions, functional groups such as a formyl, a nitro or an acetyl group could be selectively introduced on one of the two carbazoles. By combining X-ray diffraction and 2D NMR experiments, the higher reactivity of one of the two carbazoles could be clearly evidenced, enabling to generate asymmetrically substituted structures. Thanks to this unprecedented approach on the 5,12-dihydroindolo[3,2-a]carbazole scaffold, the absorption of the resulting dyes could be shifted towards the visible range whereas the parent structure (5,12-dihexyl-6,7-diphenyl-5,12-dihydroindolo[3,2-a]carbazole) exhibits a strongly UV-centered absorption. In light of their visible light absorption properties, several dyes have been examined as photoinitiators of polymerization activable at 405 nm and under low light intensity in two-component photoinitiating systems for the free radical polymerization of acrylates or the cationic polymerization of epoxides. Chemical mechanisms supporting the different polymerization processes have been fully elucidated by combining several techniques including cyclic voltammetry, UV–visible absorption and photoluminescence spectroscopy as well as photolysis experiments.

Free radical polymerization of acrylates bearing acetylene for preparation of clickable polymers

It is still a challenge to directly, without any control means, synthesize polymers bearing acetylene groups by normal free radical polymerization (FRP) of acetylenyl vinyl monomers, such as propargyl (meth)acrylates, because the reactive acetylene groups result in chain branching and gelation. Some propargyl acrylates with alkyl substitutes, however, can afford linear and soluble polymers. To clarify the substitute effects the FRP behaviours of a series of acrylates bearing acetylene groups with or without substitutes are studied. Homopolymerizations of acetylenyl acrylates without or with mono-substitute on propargyl led to branched polymers at early reaction stage, and became gelled after 0.5 h with monomer conversion over 12% and gel content over 50%. The acetylenyl acrylates with di-substitutes on propargyl can afford linear and soluble homo- and copolymers with‾Mn up to over 10,000 and with 45–75% monomer conversion, except for monomer 2-(2-methylbut-3-yn-2-yloxy)ethyl acrylate (DMPOEA) which has di-substitutes and a spacer connecting to the propargyl. Reactivities of vinyl and acetylene groups were found within 20 times difference by laser flash photolysis (LFP) experiments. The substitute effects of acetylenyl acrylates on FRP are explained by the intramolecular cycloaddition between CC and CC to form lactone from the s-cis conformers of the di-alkyl substituted acetylenyl acrylates. Propagating radicals can transform to stable allyl radicals by α-H atom transfer and thus the chain propagations stop. Both real-time FT-IR monitoring of photo-polymerization and high resolution 13C NMR spectra of the polymer confirmed the existence of lactone units on polymer chains. The hypothesis is also accordance with facts obsorved in the FRP. Finally postpolymerization modification through acetylene groups on polymer chains by photo thiol-yne click reaction is exemplified.

Recent Advances in bis-Chalcone-Based Photoinitiators of Polymerization: From Mechanistic Investigations to Applications.

Over the past several decades, photopolymerization has become an active research field, and the ongoing efforts to develop new photoinitiating systems are supported by the different applications in which this polymerization technique is involved—including dentistry, 3D and 4D printing, adhesives, and laser writing. In the search for new structures, bis-chalcones that combine two chalcones’ moieties within a unique structure were determined as being promising photosensitizers to initiate both the free-radical polymerization of acrylates and the cationic polymerization of epoxides. In this review, an overview of the different bis-chalcones reported to date is provided. Parallel to the mechanistic investigations aiming at elucidating the polymerization mechanisms, bis-chalcones-based photoinitiating systems were used for different applications, which are detailed in this review.

Remote effect of substituents on the properties of phenyl thienyl thioether-based oxime esters as LED-sensitive photoinitiators

Visible light-sensitive photoinitiators (PIs) are essential for light-emitting diode (LED) photopolymerization as LEDs are becoming the predominant light sources. In this work, five phenyl thienyl thioether-based oxime esters with different electron-donating and -withdrawing substituents on the para-position of the phenyl ring were designed and synthesized as LED-sensitive PIs. These oxime esters exhibited a maximum absorption band matched with the LED emission spectra (e.g., 365–425 nm). The remote substituents clearly affected the absorption of the oxime esters, and the principle was investigated via DFT calculations. The substituents also enhanced the initiation activities with the increase in the quantum yields of photo-induced free radical generation. Besides, upon comparison of the quantum yields of fluorescence, photolysis, and free radicals, a fast intersystem crossing was proposed for the excited states of these oxime esters, and results revealed the photoreactions were mainly from the triplet states. Finally, photo-DSC was employed to evaluate the actual photopolymerization. Results suggested that they could all efficiently initiate the free radical polymerization of acrylates under LED irradiation, making them suitable PIs for LED polymerization. This study could provide some significance to the design of PIs with improved efficiency.

N-ethyl carbazole-1-allylidene-based push-pull dyes as efficient light harvesting photoinitiators for sunlight induced polymerization

In this article, the free radical polymerization of acrylates was successfully achieved with a series of twelve push-pull chromophores comprising the N-ethyl carbazole-1-allylidene group as the electron-donating group. Using this strong donor, the resulting dyes, never synthesized before, could efficiently initiate the free radical photopolymerization of acrylates upon mild irradiation conditions e.g. using sunlight. These novel multi-component systems comprising the above mentioned push-pull dyes, a tertiary amine (ethyl dimethylaminobenzoate EDB) and an iodonium salt could act as efficient photoinitiating systems (PISs) in free radical polymerization (FRP), leading to the formation of 3D patterns with precise shapes under the direct laser write (DLW) approach. Among these new PISs, dyes 3, 6, 7 and 8 were selected due to their efficient photoinitiation performances for chemical mechanism studies including steady state photolysis, fluorescence quenching measurements, electron spin resonance (ESR) spin-trapping experiments and cyclic voltammetry. Markedly, their excellent photochemical reactivities prompted us to investigate the performance of these multi-component photoinitiating systems upon sunlight as an ecofriendly approach. As a result, this research proved that sunlight could be used as a potential light source that can advantageously replace LEDs when highly reactive push-pull dyes are used as photosensitizers for the free radical photopolymerization of acrylate resins. Finally, 3D patterns could be prepared with the new photocomposites, and silica fillers could be even incorporated within the photosensitive resins so that a gradient of resolution could be successfully demonstrated.

Design of photoinitiating systems based on the chalcone-anthracene scaffold for LED cationic photopolymerization and application in 3D printing

In this study, light-emitting diodes (LEDs) used as secure, low-cost and possessing long emission wavelengths irradiation sources were applied in photopolymerization. Seven novel anthracene derivatives (noted A1-A7) were proposed and evaluated in photosensitive systems. Three of them were never synthesized before (A1, A2 and A7) and the other derivatives were evaluated in other fields. Due to the in-silico design of molecular structure by molecular modeling, the proposed chalcone-anthracenes showed a broad absorption band in the visible region with favorable molar extinction coefficients. Photoinitiation abilities of the different photoinitiating systems were examined by the Real-Time Fourier Transformed Infrared Spectroscopy. The free radical polymerization of acrylates under LED@405 nm irradiation in laminate was evaluated and high final function conversions (FCs) were obtained in the presence of three-component photoinitiating systems based on chalcone-anthracenes/iodonium salt/amine. Meanwhile, the chalcone-anthracene derivatives exhibited high photoinitiation abilities in cationic photopolymerization of epoxides in combination with an iodonium salt under LED@405 nm irradiation. The final function conversions of epoxy using some anthracene/iodonium salt systems were even higher than the well-established dibutoxyanthracene (DBA)/iodonium salt benchmark system. In addition, due to the good light absorption properties, the cationic photopolymerization also was carried out in the presence of the chalcone-anthracene/iodonium salt systems under LED@470 nm or laser diode@447 nm irradiation (not possible to do with the reference DBA systems). Markedly, these derivatives were also able to sensitize sulfonium salts. The photochemical reactivity of anthracene derivatives was investigated through the steady state photolysis and fluorescence quenching experiments. Furthermore, the proposed interaction mechanisms of chalcone-anthracene derivatives and additives (iodonium salt and amine) were discussed using the free energy changes of electron transfer reactions. Interestingly, the cationic photopolymerization of A5/iodonium salt system was applied in 3D printing and the 3D patterns showed a good spatial resolution.

Jacket temperature regulation allowing well-defined non-adiabatic lab-scale solution free radical polymerization of acrylates

Conventional batch solution free radical polymerization of n-butyl acrylate with thermal initiators such as AIBN is known to be strongly exothermic and influenced by highly activated side reactions such as backbiting and β-scission.

Design of ketone derivatives as highly efficient photoinitiators for free radical and cationic photopolymerizations and application in 3D printing of composites

AbstractHerein, thirteen ketone derivatives composed of different cyclohexanone cores and peripheral moieties are designed, among which 10 ketones have never been synthesized before. These ketones are proposed as high‐performance photoinitiators for both free radical polymerizations and cationic polymerizations under soft conditions (visible LED@405 nm irradiation at room temperature). In combination with an amine and an iodonium salt (Iod), these ketones could be used in three−component photoinitiating systems to initiate the free radical polymerization of acrylates with distinct final conversions, among which the ketone−1/amine/Iod combination proved to be the most efficient one. Besides, the ketone−1/Iod two−component system also showed a remarkable photoinitiation ability for the cationic polymerization of epoxides. The photochemical sensitivity of ketone−1 in the presence of an amine and an iodonium salt was systematically investigated by steady state photolysis and excited state fluorescence quenching characterizations, respectively. Interestingly, macroscopic 3D patterns with excellent spatial resolution could be generated using the ketone−1/amine/Iod photoinitiating system for the free radical polymerization of acrylates. This high performance is also found useful to overcome the light penetration issue for the access to filled samples (silica) and the preparation of composites.

Novel Push–Pull Dyes Derived from 1H-cyclopenta[b]naphthalene-1,3(2H)-dione as Versatile Photoinitiators for Photopolymerization and Their Related Applications: 3D Printing and Fabrication of Photocomposites

A series of eleven push–pull chromophores with specific structures have been designed for the free radical polymerization of acrylates, but also for the fabrication of photocomposites and 3D-printed structures. New photoinitiating systems comprising the different push–pull dyes showed excellent photochemical reactivities at 405 nm. Notably, polymerization reactions could be initiated with light-emitting diodes (LEDs) which constitute a unique opportunity to promote the free radical polymerization under mild conditions, i.e., low light intensity (e.g., sunlight) and under air. Photopolymerization is an active research field, and push–pull dyes have already been investigated for this purpose. Besides, it remains of crucial interest to investigate new reactive structures capable of efficiently initiating photopolymerization reactions. The plausible potential of these structures to act as efficient photoinitiators in vat photopolymerization (or 3D printing) and fabrication of photocomposites prompts us to select eleven new push–pull dyes to design multi-component photoinitiating systems activable with LEDs emitting at 405 nm. Precisely, a tertiary amine, i.e., ethyl dimethylaminobenzoate (EDB) used as an electron/hydrogen donor and an iodonium salt used as an electron acceptor were selected to behave as powerful co-initiators to construct three-component photoinitiating systems (PISs) with the different push–pull dyes. Among these new PISs, dye 8 and 9-based PISs could efficiently promote the free radical photopolymerization of acrylates upon exposure to a LED emitting at 405 nm also upon sunlight irradiation, highlighting their huge performance. Photoinitiating abilities could be explained on the basis of steady state photolysis experiments. Fluorescence measurements and electron spin resonance (ESR) spin-trapping experiments were also performed to obtain a deeper insight into the chemical mechanisms supporting the polymerization reaction and determine the way the initiating species, i.e., the radicals, are observed. Finally, two investigated dye-based PISs were applied to the fabrications of photocomposites. Three-dimensional patterns with excellent spatial resolutions were generated by the laser writing technique to identify the effects of photopolymerization of acrylates both in the absence and presence of fillers (silica). Interestingly, comparison between the 3D objects fabricated by the PISs/monomer systems and the PISs/monomer/filler photocomposites indicates that the newly designed photocomposites are suitable for practical applications.

Allyloxy ketones as efficient photoinitiators with high migration stability in free radical polymerization and 3D printing

Five ketone derivatives (ketone-1~ketone-5) never synthesized in the literature and containing the same peripheral 1,3-bis(allyloxy)benzene substituting group but different central cyclohexanone cores were designed and proposed as high-performance photoinitiators for the free radical polymerization of acrylates under mild conditions. In combination with an amine and an iodonium salt (Iod), these ketones could initiate the photopolymerization of di(trimethylolpropane) tetraacrylate (TA), a tetrafunctional acrylates monomer, upon visible LED irradiation at room temperature in both thick films (1.4 mm) and thin films (25 μm) conditions. The distinct photopolymerization profiles of acrylates were studied by real time Fourier transform infrared spectroscopy, which indicated that the ketone-2/amine/Iod system could induce the highest final conversion of acrylates in thick films condition, while ketone-5/amine/Iod system could induce the highest final conversion of acrylates in thin films condition. Photoreactivity of ketone-2 and ketone-5 was systematically investigated by steady state photolysis and fluorescence quenching experiments in the presence of an amine and an iodonium salt, respectively. Moreover, eminent migration stability of ketones in photocured TA was observed. Finally, the ketone-2 and ketone-5-based three-component photoinitiating systems were applied for the laser writing experiments of TA, and macroscopically tridimensional patterns were fabricated with an excellent spatial resolution.

Ketone derivatives as photoinitiators for both radical and cationic photopolymerizations under visible LED and application in 3D printing

Six ketones (abbreviated as ketones 1–6) varying by the substitution pattern of the central cyclohexanones and the choice of the peripheral groups (thiophene or furane) were synthesized and proposed as unprecedented visible light sensitive photoinitiators, in combination with an amine and an iodonium salt, for the free radical polymerization of acrylates upon LED irradiation at 405 nm. For the photopolymerization of acrylates carried out as thin samples in laminate, all these ketones showed high photoinitiating abilities. Conversely, when tested as photoinitiators for thick samples, compared to the other 4 ketones, ketone 3 and ketone 5 both based onpiperidin-4-one as the central core and comprising furanes as peripheral groups proved to be the most efficient photoinitiators. Notably, the highest final polymerization conversion of Ebecryl 40, a tetrafunctional polyether acrylate, could be obtained using these two photoinitiators. The high photoreactivity of ketone 3 was highlighted by the steady state photolysis experiments. Meanwhile, ketone 3 could also promote the cationic polymerization of epoxides upon LED irradiation at 405 nm, in the presence of an iodonium salt. Interestingly, some 3D patterns could also be fabricated by free radical polymerization of Ebecryl 40 while using the ketone 3-based photoinitiating system.

Novel ketone derivative-based photoinitiating systems for free radical polymerization under mild conditions and 3D printing

Novel ketone derivatives as efficient photoinitiators for the free radical polymerization of acrylates and application in 3D printing.

Design of Iodonium Salts for UV or Near-UV LEDs for Photoacid Generator and Polymerization Purposes.

Iodonium salts are well established photoacid generators, cationic photoinitiators, as well as additives commonly used in photoredox catalytic cycles. However, as a strong limitation, iodonium salts are characterized by low light absorption properties for λ > 300 nm so that these latter cannot be activated with cheap, safe, and eco-friendly near UV or even visible light emitting diodes (LEDs). To overcome this drawback, the covalent linkage of an iodonium salt to a chromophore absorbing at longer wavelength is actively researched. With aim at red-shifting the absorption spectrum of the iodonium salt, the synthesis of new compounds combining within a unique chemical structure both the chromophore (here the naphthalimide scaffold) and the iodonium salt is presented. By mean of this strategy, a polymerization could be initiated at 365 nm with the modified iodonium salts whereas no polymerization could be induced with the benchmark iodonium salt i.e., Speedcure 938 at this specific wavelength. To examine the effect of the counter-anion on the photoinitiating ability of these different salts, five different counter-anions were used. Comparison between the different anions revealed the bis(trifluoromethane)sulfonimide salt to exhibit the best photoinitiating ability in both the free radical polymerization of acrylates and the cationic polymerization of epoxides. To support the experimental results, molecular orbital calculations have been carried out. By theoretical calculations, the initiating species resulting from the photocleavage of the iodonium salts could be determined. The cleavage selectivity and the photochemical reactivity of the new iodoniums are also discussed.