Synthesis and photoinitiating behavior of hyperbranched polymeric photoinitiators bearing coinitiator amine

A series of benzophenone (BP)‐terminated hyperbranched polyester (BoltornTM P1000), bearing amine moieties as synergists by reacting with piperidine, were synthesized as yellowish liquids with low viscosity, and used as polymeric photoinitiators (HPPIs). For comparison, acrylate groups were introduced to the terminals of hyperbranched polyester for obtaining a polymerizable photoinitiator. The chemical structures were characterized by FTIR and ¹H NMR spectroscopy. HPPIs and BP exhibited the similar absorptions by UV–vis spectroscopy. The photoinitiating behavior of HPPIs with trimethylolpropane triacrylate (TMPTA) as a trifunctional monomer was investigated by using photo‐DSC analysis. The results indicated that the maximum photopolymerization rate and unsaturation conversion of TMPTA initiated by HPPIs were both lower than that by BP. Among them, the HPPI with double tertiary amine moiety of BP moiety was found to be the most efficient photoinitiator. Additionally, the films cured with bisphenol A epoxy acrylate EB605 initiated by HPPIs were uniform and possessed high T_g from DMTA. Copyright © 2010 John Wiley & Sons, Ltd.     

Visible light‐emitting diode‐sensitive thioxanthone derivatives used in versatile photoinitiating systems for photopolymerizations

Novel thioxanthone (TX) derivatives are used as versatile photoinitiators upon visible light‐emitting diode (LED; e.g., 405, 425, and 450 nm) exposure. The mechanisms for the photochemical generation of reactive species (i.e., cations and free radicals) produced from photoinitiating systems based on the photoinitiator and an iodonium salt, tris(trimethylsilyl)silane, or an amine, were studied by UV–vis spectroscopy, fluorescence, cyclic voltammetry, steady‐state photolysis, and electron spin resonance spin‐trapping techniques. The reactive species are particularly efficient for cationic, free radical, hybrid, and thiol‐ene photopolymerizations upon LED exposure. The optimized photoinitiating systems exhibit higher efficiency than those of reference systems (i.e., isopropyl TX‐based photoinitiating systems), especially in the visible range. According to their beneficial features, these photoinitiating systems have considerable potential in photocuring applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 4037–4045     

Naphthalimide‐phthalimide derivative based photoinitiating systems for polymerization reactions under blue lights

Naphthalimide‐phthalimide derivatives (NDPDs) have been synthesized and combined with an iodonium salt, N‐vinylcarbazole, amine or 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine to produce reactive species (i.e., radicals and cations). These generated reactive species are capable of initiating the cationic polymerization of epoxides and/or the radical polymerization of acrylates upon exposure to very soft polychromatic visible lights or blue lights. Compared with the well‐known camphorquinone based systems used as references, the novel NDPD based combinations employed here demonstrate clearly higher efficiencies for the cationic polymerization of epoxides under air as well as the radical polymerization of acrylates. Remarkably, one of the NDPDs (i.e., NDPD2) based systems is characterized by an outstanding reactivity. The structure/reactivity/efficiency relationships of the investigated NDPDs were studied by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The key parameters for their reactivity are provided. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 665–674     

Aminothiazonaphthalic anhydride derivatives as photoinitiators for violet/blue LED‐Induced cationic and radical photopolymerizations and 3D‐Printing resins

The cations and radicals produced in aminothiazonaphthalic anhydride derivatives (ATNAs) combined with an iodonium salt, N‐vinylcarbazole, amine, or chloro triazine initiate the ring‐opening cationic polymerization of epoxides and the free radical polymerization of acrylates under LEDs at 405 or 455 nm. The photoinitiating ability of these novel photoinitiating systems is higher than that of the well‐known camphorquinone‐based systems. An example of the high reactivity of the new proposed photoinitiator is also provided in resins for 3D‐printing using a LED projector@405 nm. The chemical mechanisms are investigated by steady‐state photolysis, cyclic voltammetry, fluorescence, laser flash photolysis, and electron spin resonance spin‐trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1189–1196     

Blue LED light‐sensitive benzo pyrazolo (or imidazo) isoquinolinone derivatives in high‐performance photoinitiating systems for polymerization reactions

Isoquinolinone derivatives (IQ) have been synthesized and combined with different additives (an amine, 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine, an iodonium salt, or N‐vinylcarbazole) to produce reactive species (i.e. radicals and cations) being able to initiate the radical polymerization of acrylates, the cationic polymerization of epoxides, the thiol‐ene polymerization of trifunctional thiol/divinylether, and the synthesis of epoxide/acrylate interpenetrated polymer network IPN upon exposure to very soft polychromatic visible lights, blue laser diode or blue LED lights. Compared with the use of camphorquinone based systems, the novel combinations employed here ensures higher monomer conversions (～50–60% vs. ～15–35%) and better polymerization rates in radical polymerization. The chemical mechanisms are studied by steady‐state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin trapping techniques. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 567–575     

A benzophenone‐naphthalimide derivative as versatile photoinitiator of polymerization under near UV and visible lights

A benzophenone‐naphthalimide derivative (BPND) bearing tertiary amine groups has been developed as a high‐performance photoinitiator in combination with 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine or an iodonium salt for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon exposure to near UV and visible LEDs (385–470 nm). BPND can even produce radicals without any added hydrogen donor. The photochemical mechanisms are studied by molecular orbital calculations, steady state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry and laser flash photolysis techniques. These novel BPND based photoinitiating systems exhibit an efficiency higher than that of the well‐known camphorquinone‐based systems (FRP and CP) or comparable to that of bis(2,4,6‐trimethylbenzoyl)‐phenylphosphineoxide (FRP at λ ≤ 455 nm). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 445–451     

Azahelicenes as visible light photoinitiators for cationic and radical polymerization: Preparation of photoluminescent polymers and use in high performance LED projector 3D printing resins

In this article, novel azahelicenes (AZs) were synthesized and proposed as high performance visible light photoinitiators for both the free radical polymerization of acrylates and the cationic polymerization (CP) of epoxides upon visible light exposure using Light Emitting Diodes (LEDs) @405, @455, and @470 nm. Excellent polymerization initiating abilities are found and high final conversions were obtained. Remarkably, an exceptional long lifetime photoluminescence property of the polymer films was observed when synthesized in presence of AZs. A full picture of the involved chemical mechanisms is given. AZs being high performance photoinitiators, their use in new cationic LED 3D printing resins will be also presented, that is, the cationic process upon LED projector @405 nm can be useful to reduce the shrinkage usually observed for radical polymerization. LED projector printing is very interesting compared to laser writing as this technology projects the profile of an entire layer of a 3D object at one time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1189–1199     

Iron complexes as photoinitiators for radical and cationic polymerization through photoredox catalysis processes

Six iron complexes (FeCs) with various ligands have been designed and synthesized. In combination with additives (e.g., iodonium salt, N‐vinylcarbazole, amine, or chloro triazine), the FeC‐based systems are able to efficiently generate radicals, cations, and radical cations on a near UV or visible light‐emitting diode (LED) exposure. These systems are characterized by an unprecedented reactivity, that is, for very low content 0.02% FeC‐based systems is still highly efficient in photopolymerization contrary to the most famous reference systems (Bisacylphosphine oxide) illustrating the performance of the proposed catalytic approach. This work paves the way for polymerization in soft conditions (e.g., on LED irradiation). These FeC‐based systems exhibit photocatalytic properties, undergo the formation of radicals, radical cations, and cations and can operate through oxidation or/and reduction cycles. The photochemical mechanisms for the formation of the initiating species are studied using steady state photolysis, cyclic voltammetry, electron spin resonance spin trapping, and laser flash photolysis techniques. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 42–49     

Iodonium sulfonates as high‐performance coinitiators and additives for CQ‐based systems: Toward aromatic amine‐free photoinitiating systems

Iodonium sulfonates are proposed here as a new class of high‐performance coinitiators for camphorquinone (CQ)‐based systems for the polymerization of methacrylates under blue light irradiation. When combined with CQ, the new proposed coinitiators present excellent polymerization performances and are excellent candidates for the replacement of tertiary aromatic amines subjected to toxicological concerns in the well‐established CQ/amine photoinitiating system (PIS). Remarkably, good bleaching properties are obtained after polymerization. The use of the new PIS for dental adhesives is also investigated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1664–1669     

Naphthalic anhydride derivatives: Structural effects on their initiating abilities in radical and/or cationic photopolymerizations under visible light

Only one naphthalic anhydride derivative has been reported as light sensitive photoinitiator, this prompted us to further explore the possibility to prepare a new family of photoinitiators based on this scaffold. Therefore, eight naphthalic Naphthalic anhydride derivatives (ANH1‐ANH8) have been prepared and combined with an iodonium salt (and optionally N‐vinylcarbazole) or an amine (and optionally 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine) to initiate the cationic polymerization of epoxides and the free radical polymerization of acrylates under different irradiation sources, that is, very soft halogen lamp (～ 12 mW cm^?2), laser diode at 405 nm (～1.5 mW cm^?2) or blue LED centered at 455 nm (80 mW cm^?2). The ANH6 based photoinitiating systems are particularly efficient for the cationic and the radical photopolymerizations, and even better than that of the well‐known camphorquinone based systems. The photochemical mechanisms associated with the chemical structure/photopolymerization efficiency relationships are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis, and electron spin resonance spin‐trapping techniques. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2860–2866     

Photoinitiating Characteristics of Benzophenone Derivatives as Type II Macromolecular Photoinitiators Used for UV Curable Resins

Dodecyl-benzophenone(DBP) and hexadecoxyl-benzophenone(HDBP) as type II photoinitiators used for radical photopolymerization systems were synthesized by Friedel-Crafts reaction, and characterized by 1H NMR and FTIR spectroscopy. The UV-Vis absorption spectra of DBP and HDBP, propitious to photopolymerization under a commercial mercury UV bulb are centered at 345 and 335 nm, respectively. HDBP has higher extinction coefficient than DBP, but lower photoinitiating efficiency. Their photoinitiating performances...     

Thioxanthone–carbazole as a visible light photoinitiator for free radical polymerization

A thioxanthone (TX) derivative with the additional carbazole chromophore, namely thioxanthone‐carbazole (TX‐C) was synthesized and characterized. The photophysical properties and its efficiency to polymerize methyl methacrylate both in the presence and absence of N,N‐dimethylaniline (DMA) as coinitiator was investigated and compared with that of the commercially available TX. TX‐C was found to display better photophysical properties and in both cases initiate polymerization more efficiently. Detailed real‐time Fourier transform infrared studies revealed that high polymerization rates can be obtained when TX‐C in conjunction with DMA was used. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Phenacyl onium salt photoinitiators: synthesis, photolysis, and applications

Onium salts, namely sulfonium, phosphonium, ammonium, and pyridinium salts containing phenacyl group are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers, which are not polymerizable by a free-radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the salts. Depending on the type of the salt, the direct photoinitiation of cationic polymerization involves reversible or irreversible processes. The photolysis of phenacylsulfonium compounds proceeds by a reversible process, while the other types undergo irreversible photolysis leading to complete fragmentation of the photoinitiator. An additionally useful tool, namely photosensitized generation of initiating species enlarges the versatility of these salts as photoinitiators. Photoinitiated free-radical and zwitterionic polymerizations by using phenacyl-type salts are also addressed. Keto-enol tautomerization of phenacyl pyridinium salts is discussed. Moreover, an interesting application concerning in situ synthesis of clay-poly(methyl methacrylate) nanocomposites with the aid of the phenacyl anilinium salt-based photopolymerization technique is noted.     

N‐methylpicolinium derivatives as the coinitiators in photoinitiating systems for vinyl monomers polymerization

Five N‐methylpicolinium derivatives were investigated to test their abilities to function as second coinitiators in free radical photopolymerization initiated by N,N′‐diethylcarbocyanine—n‐butyltriphenylborate photoredox pair ( P19B2 ). As it is shown by the kinetic data, an addition of picolinium derivatives into P19B2 photoinitiating system visibly increases the efficiency of photoinitiation. The results suggest that the rates of photoinitiation depend on the rate of the picolyl radicals formation. The redox potentials of tested N‐methylpicolinium derivatives were measured and the calculation of free energy change for the possible electron transfer reactions between all components of the system (both stable and transient individuals) was performed. The results suggest that cyanine dyes are able to start a specific chain of an electron transfer reactions involving different coinitiators (borate salt and N‐alkylpicolinium derivatives), giving as a result one photon—two‐radicals photochemical response. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 576–588, 2009     

Naphthodioxinone‐1,3‐benzodioxole as photochemically masked one‐component type II photoinitiator for free radical polymerization

A 1,3‐benzodioxole derivative of naphthodioxinone, namely 2‐(benzo[d][1,3]dioxol‐5‐yl)‐9‐hydroxy‐2‐phenyl‐4H‐naphtho[2,3‐d][1,3]dioxin‐4‐one was synthesized and characterized. Its capability to act as caged one‐component Type II photoinitiator for free radical polymerization was examined. Upon irradiation, this photoinitiator releases 5‐benzoyl‐1,3‐benzodioxole possessing both benzophenone and 1,3‐dioxole groups in the structure as light absorbing and hydrogen donating sites, respectively. Subsequent photoexcitation of the benzophenone chromophore followed by hydrogen abstraction generates radicals capable of initiating free radical polymerization of appropriate monomers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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

Herein, 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.     

Phenacyl Ethyl Carbazolium as a Long Wavelength Photoinitiator for Free Radical Polymerization

A new phenacyl‐type photoinitiator based on ethyl carbazole as a long wavelength photo­initiator is developed for free radical polymerization. Phenacyl ethyl carbazolium hexafluoroantimonate (PECH) photoinitiator is synthesized in a two‐step, one‐pot manner by quaternizing ethyl carbazole with phenacyl bromide and subsequent ion exchange reaction with potassium hexafluoroantimonate. Under irradiation, PECH tends to undergo homolytic bond cleavage bringing about initiating free radicals. However, as evidenced by cyclic voltammetry and real‐time photobleaching studies, formation of initiating cationic species is highly unlikely as the photochemically formed charged carbazole units tend to couple.

     

Copper and iron complexes as visible‐light‐sensitive photoinitiators of polymerization

The utilization of visible lights for the fabrication of polymeric materials is recognized as a promising and environmentally friendly approach. This process relies on the photochemical generation of reactive species (e.g., radicals, radical cations, or cations) from well‐designed photoinitiators (PIs) or photoinitiating systems (PISs) to initiate the polymerization reactions of different monomers (acrylates, methacrylates, epoxides, and vinyl ethers). In spite of the fact that metal complexes such as ruthenium‐ or iridium‐based complexes have found applications in organic and polymer synthesis, the search of other low‐cost metal‐based complexes as PISs is emerging and attracting increasing attentions. Particularly, the concept of the photoredox catalysis has appeared recently as a unique tool for polymer synthesis upon soft conditions (use of light emitting diodes and household lamp). This highlight focuses on recently designed copper and iron complexes as PI catalysts in the application of photoinduced polymerizations (radical, cationic, interpenetrated polymer networks, and thiol‐ene) or controlled radical polymerization under visible light irradiation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2673–2684     

Dibenzophenazine derivatives as visible photosensitizers for diaryliodonium salts

The use of two dibenzo[a,c]phenazine derivatives, 10,13‐bis(2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl)dibenzo[a,c]phenazine and 10,13‐bis(4‐hexylthiophen‐2‐yl)dibenzo[a,c]phenazine are reported as photosensitizers for diaryliodonium salt photoinitiators. Novel dyes based on the dibenzo[a,c]phenazine skeleton are shown to be efficient in carrying out the cationic photopolymerizations. Representative examples of different types of monomers including epoxide, and vinyl monomers are polymerized in the presence of the photosensitizers and diphenyliodonium hexafluorophosphate (Ph₂I⁺PF). Polymerizations are initiated at room temperature using long wavelength UV and visible light, and monitored by optical pyrometry. The photopolymerization of an epoxide monomer via solar irradiation is also demonstrated. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011