Three component ketocoumarin, amine, maleimide photoinitiator I

An N-substituted maleimide has been used in conjunction with ketocoumarins and a tertiary amine to initiate the polymerization of 1,6-hexanedioldiacrylate in both the UV (365/366 nm) and visible region (436 nm) of the electromagnetic spectrum. The rate of polymerization of three ketocoumarin/tertiary amine combinations are significantly increased by the addition of a N-substituted maleimide, presumably due to oxidation of the coumarin ketyl radical formed by interaction between the triplet state of the ketocoumarin and the tertiary amine.     

Synthesis and characterization of copolymerizable one‐component type II photoinitiator

A copolymerizable one‐component Type II photoinitiator (CMEBP), based on 4‐hydroxybenzophenone (HBP), epichlorohydrin, morpholine, and acryloyl chloride, was synthesized and its structure was confirmed by ¹H‐NMR. The properties of CMEBP were investigated with UV spectroscopy and photo‐differential scanning calorimetry (photo‐DSC). The maximum of UV absorption red‐shifted significantly compared to benzophenone (BP). Photopolymerization results of tripropylene glycol diacrylate (TPGDA) indicated that CMEBP had larger maximum rate of polymerization than that of BP/triethanolamine (TEOHA) and HBP/triethylamine (TEA), larger final double bond conversion than that of HBP/TEA, but lower than that of BP/TEOHA. The rate of polymerization, final conversion increased and the induction period shortened with increase in CMEBP concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

One‐component photoinitiator based on benzophenone and sesamol

A new benzodioxole derivative, 4‐(1,3‐benzodioxol‐5‐yloxy) benzophenone (BPBDO), based on benzophenone and sesamol was precisely synthesized, and it can be used as a 1‐component type II photoinitiator. Elementary analysis, atmospheric pressure chemical ionization mass spectrometry, ¹H nuclear magnetic resonance, and ¹³C nuclear magnetic resonance studies revealed that the molecular structure of BPBDO consisted of both benzophenone (BP) and benzodioxole (BDO) structures. The laser flash photolysis experiments and electron spin resonance test indicated that the process of radicals generated from BPBDO after irradiation was similar to 3 processes of ethyl 4‐dimethylaminobenzoate and BP. The kinetics of photopolymerization of the photoinitiator was also studied by real‐time infrared spectroscopy. The oxygen content, light intensity, and viscosity of the monomer affected the decomposition (R_d) and polymerization rate, and the final double bond conversion was also studied. All the results suggest that BPBDO is a 1‐component photoinitiator that is an efficient photoinitiator for free radical polymerization. In contrast to typical dual‐component photoinitiators, eg, BP/ethyl 4‐dimethylaminobenzoate or BP/BDO, BPBDO does not require an additional amine coinitiator for the initiation and is applicable in nonamine resin systems.     

Novel,highly efficient polymeric benzophenone photoinitiator containing coinitiator moieties for photopolymerization

A novel polymeric photoinitiator P(MPBP‐co‐DMAEMA), bearing side‐chain benzophenone (BP) and coinitiator amine, was synthesized through free radical copolymerization of a polymerizable photoinitiator, 4‐[(4‐maleimido)phenoxy]benzophenone (MPBP), and a polymerizable coinitiator amine, N, N‐dimethylaminoethyl methacrylate (DMAEMA). In order to find out the influences of coinitiator amine on photopolymerization, a polymeric coinitiator amine, P(DMAEMA), was also synthesized for comparison. FT‐IR, ¹H NMR, and GPC analyses confirm the structures of polymers. The UV‐Vis spectra of polymeric photoinitiator P(MPBP‐co‐DMAEMA) and polymerizable photoinitiator MPBP are similar, and both exhibit high red‐shifted maximal absorption as compared with BP. The photopolymerization of 1,6‐hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA), initiated by MPBP/DMAEMA, MPBP/P(DMAEMA), and P(MPBP‐co‐DMAEMA) systems, was studied by photo‐DSC. The results indicate that P(MPBP‐co‐DMAEMA) is most efficient for the polymerization of both HDDA and TMPTA, and MPBP/P(DMAEMA) is the least efficient of the three photoinitiating systems. Copyright © 2009 John Wiley & Sons, Ltd.     

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     

Photopolymerization of maleimide perfluoropolyalkylethers without a photoinitiator

Perfluoropolyalkylethers derived from hexafluoropropylene oxide were functionalized with maleimide groups. Irradiated by UV‐light, the new maleimide macromonomers demonstrated very fast polymerization kinetics with a curing time as fast as 8 s. The effect on photopolymerization of different features such as the molecular weight of the fluorinated chain and the chain length of the hydrogenated spacer were studied, as well as the influence of the type of photoinitiator and the presence of air. Thermal and surface properties of the UV‐cured polymers were examined and were typical to fluoropolymers in view of water–oil repellent coatings. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 699–707     

Novel PU‐type polymeric photoinitiator comprising side‐chain benzophenone and coinitiator amine for photopolymerization of PU acrylate

A novel diamine 3,5‐diamino‐4′‐phenoxylbenzophenone (DAPBP) was synthesized from the reaction of 3,5‐diamino‐4′‐chlorobenzophenone (DACBP) and phenol. Then through the polycondensation of DAPBP, toluene‐2,4‐diisocyanate (TDI), and N‐methyldiethanolamine (MDEA), we obtained a PU‐type polymeric photoinitiator containing side‐chain benzophenone (BP) and tertiary amine in the same macromolecule (PUSOA). Another polymeric photoinitiator without coinitiator amine in polymer chain (PUSO) was also synthesized for comparison. FT‐IR, ¹H NMR, and GPC analyses confirmed the structures of monomer and polymeric photoinitiators. The UV–Vis spectra of PUSOA, PUSO, and DAPBP are similar, and all exhibit the maximal absorption near 290 nm. ESR spectra indicate that PUSOA can generate active species most efficiently. The photopolymerization of PU acrylate, initiated by PUSOA, PUSO/MDEA, DAPBP/MDEA, and BP/MDEA, was studied by differential scanning photocalorimetry (photo‐DSC). The results show that the in‐chain coinitiator amine can significantly improve the photoefficiency of the polymeric photoinitiator and the PUSOA is more efficient for the polymerization of PU acrylate than its low‐molecular‐weight counterpart. Copyright © 2008 John Wiley & Sons, Ltd.     

Bifunctional maleimide dyes as selective anion sensors

A class of disubstituted maleimide dyes with two symmetrical NH binding sites was found to exhibit distinct color change and fluorescence quenching effect for fluoride, cyanide, and dihydrogen phosphate anions. The intense red emission displayed apparent solvatochromic shift, indicating a strong charge-transfer character. The interactions between the dyes and anions were variable depending on the amine substituents at C(3,4) of the maleimides. For the dyes with two pyrrolyl receptor sites, the NH protons were deprotonated by more basic anions such as fluoride or cyanide. For those with two indolyl receptor sites, formation of a chelate with H₂PO₄⁻ through hydrogen bonds played a major role.     

Photopolymerization of styrene,p-chlorostyrene,methyl methacrylate,and butyl methacrylate with polymethylphenylsilane as photoinitiator

The rates of photochemical polymerization of styrene (St), p-chlorostyrene (Cl-St), methyl methacrylate (MMA), and butyl methacrylate (BMA) with polymethylphenylsilane (PMPS) as an initiator were measured. Polymethylphenylsilane is photodegrated to form silyl radicals that may initiate polymerization of vinyl monomers. Rate constants k_p and k_t have been determined for these systems. A good correlation (log P = α + βμ) of the resonance stabilization (P) of the chain radicals and the dipole moment (μ) of the monomers is observed for these polymerization systems. This equation may be used to estimate the resonance stabilization (P) of a monomer and the polymerization rate constant (k_p). © 1996 John Wiley & Sons, Inc.     

p-Nitroacetanilide in the presence of triethylamine as a photoinitiator system for vinyl polymerization

The polymerization rate of methyl methacrylate photosensitized by p-nitroacetanilide in the presence of triethylamine was measured as a function of the amine and monomer concentrations. The polymerization proceeds readily in high-polarity media (acetonitrile/monomer) but is negligible in nonpolar media. The polymerization rate increases with the amine concentration up to 0.15M. Further increase in amine concentration does not change the polymerization rate. A similar behavior was observed for the photobleaching of the nitro compound. ESR studies show the formation of a nitro and an amine free radical, the latter free radical being the active species that adds to the monomer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3095–3100, 1997     

Photochemistry and photopolymerization activity of p-nitroaniline in the presence of N,N-dimethylaniline as a bimolecular photoinitiator system

The photoreduction behavior of p-nitroaniline (pNA) in the presence of N,N-dimethylaniline (DMA) induced by both steady-state (365 nm) and laser (337 nm) irradiation has been analyzed. The stoichiometry of the photoreduction reaction revealed that several amino radicals derived from DMA were generated by each photoreduced pNA molecule. The polymerization kinetics of the lauryl acrylate monomer (LA) photoinitiated by the pNA/DMA system has been studied by differential scanning photocalorimetry (Photo-DSC). The rate of polymerization was found to be proportional to the square root of both the incident light and the coinitiator DMA concentration. The order of the polymerization reaction with respect to monomer and initiator concentration was determined, as well as the polymerization behavior under aerobic conditions. The polymerization efficiency of this photoinitiated system was much higher than that obtained with conventional aromatic ketone photoinitiators. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3801–3812, 1997     

Theoretical calculations of the molecular properties of maleimide and its dimer

B3LYP theoretical calculations with 6-31++G(d,p) basis set have been performed to study the infrared spectrum of maleimide and its dimer. Our calculations have shown that the dimer formation leads to a binding energy of 44.0kJmol(-1) involving two intermolecular hydrogen bonds between the amide hydrogen and a carbonyl group of two neighboring maleimides. This value is essentially due to the electrostatic interaction term. Our calculations have also revealed the vibrational changes, in terms of frequencies and IR intensities, after dimer formation. The most affected modes are associated with the NH stretching and in-plane bending bands. This behavior can be adequately interpreted by the hydrogen atomic charge and NH charge-flux based on the modified charge-charge flux-overlap model for infrared intensities. The B3LYP frequency shifts are in very good agreement with the experimental ones.     

Synthesis of a benzoxazine monomer containing maleimide and allyloxy groups

A novel benzoxazine monomer 3-（4-allyloxy）phenyl-3,4-dihydro-2H-6-（N-maleimido）-l,3-benzoxazine （AMB） was synthesized and structure was confirmed by FT-IR, 1H NMR. Thermal analysis （DSC） of AMB showed the introduction of allyloxy group melting point and exhibited a narrow and symmetric curing exothermic window.     

Benzoin type photoinitiator for free radical polymerization

Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by introduction of two methyl thioether substituents. This new benzoin derivative showed an about 50 times higher light absorption in the near‐UV spectral region and performed better than the unsubstituted benzoin in polymerization experiments in bulk solutions or films of acrylate monomers when low initiator concentrations are used. Laser flash photolysis, low temperature luminescence experiments and photoproduct studies by mass spectrometry suggest that a slow α‐cleavage mechanism (k_α = 2.2 × 10⁵ s^?1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of gradient polymer by using polysiloxane‐based photoinitiator

This paper reported a polysiloxane‐based photoinitiator (184‐AC‐Si), which was synthesized basing on traditional photoinitiator 1‐hydroxy‐cyclohexyl phenyl ketene (184) and polysiloxane. Its structure was confirmed by Hydrogen‐1 nuclear magnetic resonance (¹H NMR), real‐time infrared spectroscopy and gel permeation chromatography (GPC). Ultraviolet (UV) absorption spectra of 184‐AC‐Si showed a red‐shifted maximum absorption compared with 184. The kinetics of photopolymerization was studied by real‐time infrared spectroscopy. More importantly, because of the polysiloxane‐based photoinitiator had good ability to float up, which could be proved by X‐ray photoelectron spectroscopy, mapping energy dispersive spectroscopy, UV absorption, and GPC measurements, a convenient and simple method for preparing gradient polymer initiated by 184‐AC‐Si was successfully developed. Copyright © 2011 John Wiley & Sons, Ltd.     

Molecular dynamics in fluorinated side-chain maleimide copolymers as studied by broadband dielectric spectroscopy

A series of alternating maleimide (MI) copolymers with fluorinated side chains have been investigated using broadband dielectric spectroscopy. The side chains consist of fluoroalkane (–C _x F_2x+1, x=1, 7, 9) end groups connected to the main chain via methylene spacers. The experiments were carried out in a frequency range of 0.1 Hz to 10 MHz and at temperatures between 120 K and 500 K. The fluorinated MI copolymers show a fast sub-T _g (β) relaxation characterized by an Arrhenius-type temperature dependence with activation energy in the range of 30–37 kJ/mol. Two more processes (α and δ-like) are observed, corresponding to independent relaxations of the main chain and the fluoroalkane domains respectively. For shorter side chains, the δ-like process is not observed but instead another relaxation process, α _S , occurs at temperatures higher than either the α and δ-like processes. When compared with unfluorinated MI copolymers, the fluorinated MI copolymers show the δ-like process and a slower β-relaxation unlike their unfluorinated counterparts. A model to explain the molecular origin of the four processes is proposed, supplemented by differential scanning calorimetry and published WAXS/SAXS data.     

Photopolymerization of methyl methacrylate with azo-containing polydimethylsiloxane as photoinitiator: Effect of siloxane chain length

The kinetics of the free radical photopolymerization of methyl methacrylate (MMA) initiated by azo-containing polydimethylsiloxane (PSMAI) and azobisisobutyronitrile (AIBN) was investigated. The greater polymerization rate R_p in MMA/PSMAI systems may be due to the higher value of the initiation rate R_i and the lower value of the termination rate constant k_t than that in MMA/AIBN system. The reaction orders with respect to initiators PSMAI decreased with an increase in polydimethylsiloxane chain length (SCL) in PSMAI. The observed deviations in polymerization rate from rate equation could be explained in terms of primary radical termination. The photoinitiator efficiency Φ of initiators decreased with increase in SCL, while the ratio of the rate constants for chain termination and chain initiation by primary radical increased with SCL. The fraction β of primary radicals entering into termination in MMA/PSMAI systems were larger than that in MMA/AIBN system. © 1996 John Wiley & Sons, Inc.     

One‐component,double‐chromophoric thioxanthone photoinitiators for free radical polymerization

Two one‐component, double‐chromophoric thioxanthone photoinitiators, namely TX‐EDA and TX‐DETA were synthesized by the reaction of thioxanthone aldehyde (TX‐A) with ethylenediamine (EDA) and diethylenetriamine (DETA), respectively via a facile Schiff base reaction. Both photoinitiators were characterized by spectral analysis and photobleaching studies. DFT calculations are employed to reveal the contribution of the different orbitals to the excitation of the initiators. The double‐chromophoric nature of the initiators gives rise to an increased absorption in the near UV region when compared with the pristine TX‐A. Photoinitiated polymerization of various vinyl monomers with TX‐EDA and TX‐DETA has been investigated in the presence and absence of a co‐initiator and compared for formulations consisting of precursor TX‐A. In addition, real‐time FTIR spectroscopic studies were performed in methyl methacrylate polymerization with both initiators. The higher efficiency observed with TX‐DETA may be attributed to the additional hydrogen donating sites adjacent to nitrogen atoms. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3475–3482     

Highly efficient alginate-based macromolecular photoinitiator for crosslinking and toughening gelatin hydrogels

Constructing gelatin hydrogels through photopolymerization is getting increasingly attractive due to their excellent biocompatibility and unparalleled flexibility in fabricating complex structures. In this study, an alginate-based macromolecular photoinitiator (Alg-2959) is synthesized by grafting Irgacure2959, a widely used hydrophilic small molecular photoinitiator, onto the framework of alginate. The characterization of Alg-2959 is carried out by ¹H nuclear magnetic resonance (¹HNMR), Fourier infrared spectroscopic (FTIR), Thermogravimetric analysis (TGA), and UV–Vis absorption spectrum. It is shown that Alg-2959 can induce the polymerization of acrylate monomer poly(ethylene glycol) diacrylate (PEGDA400) and glycidyl methacrylate modified gelatin (Gel-GM) with similar initiation efficiency as Irgacure2959. Compared with the pure hydrogels prepared using Irgacure2959, the hybrid hydrogels containing Alg-2959 can be further crosslinked by Ca²⁺ to form the double-network hydrogels, which exhibit enhanced toughness and elasticity. In addition, due to the introduction of alginate, the migration stability of Alg-2959 in the hydrogel networks is significantly improved compared with Irgacure2959. These results indicate the great potential of Alg-2959 in preparing biocompatible and resilient photopolymers.     

Effects of substituent and solvent on the structure and spectral properties of maleimide derivatives

The maximum absorption wavelength , emission wavelength (λ_em) and the related oscillator strength (f) of the maleimides in the ground and first excited states were calculated by using the DFT, CIS and the time-dependent density functional theory (TD-DFT) methods, where the molecular structures were optimized by DFT/B3LYP/6-31G^* calculation. Solvent effects on the maleimides were examined using the PCM simulation at DFT/B3LYP level with the 6-31G^* basis set. For N-substituted maleimide, the substituent gives only a slight influence on the maleimide chromophore, while planar conformation of PhMLH leads to the improvement in π-delocalization from substituent to maleimide unit. For 3,4-substituted maleimide, the steric repulsion between substituent and maleimide chromophore influences the extent of π-delocalization and the molecular conformation. The calculated and λ_em of maleimides are in good agreement with the experimental data. In the gas phase, both absorption and emission peaks are red-shift as compared to the non-substituted maleimide. Under solvent environment, the more planar conformation of PhMLH shows a blue-shift in the calculated and λ_em as compared with other N-substituted maleimides. For 3,4-substituted maleimides, the effect of substitution produces the most significant spectral red-shift as compared to other maleimides.