A glance at violet LED sensitive photoinitiators based on the spiroxanthene scaffold

A novel photoinitiator based on a spiroxanthene scaffold in the presence of an iodonium salt is proposed for the cationic ring‐opening polymerization of a diepoxide, as well as for the free‐radical polymerization of an acrylate upon violet LED exposure (385 and 405 nm). Good‐to‐excellent rates of polymerization and final conversions are obtained. These systems are characterized by a higher reactivity compared with that of anthracene/iodonium salt used as reference for cationic near UV polymerization. The addition of a poly(ionic liquid) improves the cationic polymerization profiles. The photochemical mechanisms are studied by steady‐state photolysis, fluorescence, and electron spin resonance spin‐trapping techniques. Molecular orbital calculations give an insight into the light absorption properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43213.     

UV‐activated hydrosilation reaction for silicone polymer crosslinking

In this article hydrosilation was employed to achieve a fully cured three‐dimensional silicone network. The UV‐activated hydrosilation reaction was investigated focusing on the curing conditions and their relationships to physical properties. After finding the optimum catalyst concentration, it was observed that by decreasing the molecular weight of the vinyl oligomer a slight increase of the T_g value was achieved together with a complete suppression of the Tm. It was possible to fully cure samples up to 4 cm of thickness. The dark curing process was evaluated by FTIR analyses and it was evidenced an important increase on dark‐polymerization, which is dependent on the length of the UV‐irradiation time. This result shows the versatility of UV‐curing technique for silicone network formation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Polymerization efficiency of bulk‐fill dental resin composites with different curing modes

The aim of this study was to investigate the effect of four different curing modes on the polymerization efficiency of eight bulk‐fill composites. Five specimens for each material were prepared for Vickers hardness measurements. The measurements were performed at 0 and 2 or 4 mm from the top of the surface of the specimens 24 h after photopolymerization. Statistical analysis was performed with one‐way analysis of variance and Tukey post hoc tests at a level of significance of a = 0.05 where a is the the level of significance. The light‐curing mode affected the microhardness in all depths, but this influence was material‐dependent (p_mat < 0.001), where p_mat is the probability to be affected by the material. The Vickers hardness numbers of the tested composites at 0 mm ranged from 9.32 ± 0.87 to 72.58 ± 6.52 and those of the tested composites at 4 mm ranged from 5.48 ± 0.32 to 54.34 ± 2.27. The clinician has to be aware of the technical characteristics of the materials and light‐curing units (LCUs) to use the most appropriate combination of LCU, composite material, and application technique. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43392.     

High performance of the linked visible photoinitiator for free radical polymerization based on erythrosine B derivative

A novel erythrosine B derivative linked with a tertiary amine used as a visible light initiator for free radical polymerization was synthesized and characterized. For comparison, the free hydrophobic erythrosine B derivative was also synthesized and its combination with the tertiary amine was used as the separated two component photoinitiator. The linked initiator exhibited higher photoinitiator efficiency in high viscosity monomer than in low viscosity one, compared with the separated counterpart. Especially, when it was combined with iodonium salt, the further promotion of the photoinitiator efficiency was observed, compared with the separated three component system. It was found that as iodonium salt together with tertiary amine was continuously added to the formula with the linked initiator, the photoinitiator efficiency was dramatically enhanced compared with the same addition to the formula with the separated counterpart, revealing the application potential of the linked initiator. And the continuous addition of either the iodium salt or the tertiary amine to the formula only leaded to the small size increase of the photoinitiator efficiency. These results suggested that there existed an interdependent relationship between iodonium salt and tertiary amine in promoting the photoinitiator efficiency of the dye/amine/iodonium salt system. For these, the corresponding synergistic mechanism was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42361.     

Synthesis of novel macrophotoinitiator for the photopolymerization of acrylate

A new kind of macrophotoinitiator (MPI) was synthesized through the copolymerization of acrylic monomers and the polymerizable photoinitiator monomer 2959‐AA. Monomer 2959‐AA was obtained by an esterification reaction between acrylic acid (AA) and the water‐soluble photoinitiator Irgacure 2959 [2‐hydroxy‐4‐(2‐hydroxyethoxy)‐2‐methylpropiophenone]. By adjusting the monomer proportions in the MPIs, two series of MPIs with different 2959‐AA contents and different glass transition temperatures were obtained. The molecular structure of 2959‐AA was characterized by Fourier‐transform infrared spectroscopy, nuclear magnetic spectrometry, and mass spectrometry. Polymerization of 1, 6‐hexanediol diacrylate was initiated using Irgacure 2959 and 2959‐AA, and two series of MPIs to be polymerized were studied with a photo‐DSC test. Results showed that 2959‐AA had higher chemical reactivity than Irgacure 2959 because of the higher solubility of the former. It was evident from the experiments that 2959‐AA content in the MPI progressively increased the polymerization rate and monomer conversion when the glass transition temperatures of MPIs were similar. At the same 2959‐AA content, the polymerization rate slightly slowed down with increased glass transition temperature. However, the radical lifetime and polymerization time were prolonged. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40352.     

Preparation of polymer/inorganic nanoparticles composites through ultrasonic irradiation

In this paper, ultrasonic induced encapsulating emulsion polymerization was first used to prepare the novel polymer/inorganic nanoparticles composites. The behaviors of several inorganic nanoparticles (SiO₂, Al₂O₃, TiO₂) under ultrasonic irradiation, such as dispersion, crushing, and activation, were studied. The dispersion stability, morphology, and structure of the ultrasonic irradiated nanoparticles were characterized by means of transmission electron microscopy (TEM), Fourier transform infrared (FTIR), and spectrophotometry, respectively. The results show that the inorganic nanoparticles in the aqueous solution can redisperse more effectively by ultrasonic irradiation than by conventional stirring. This is the basis for preparation of polymer/inorganic nanoparticles composites. By this technique, the long‐term stable latex, which mainly consists of polymer/inorganic nanoparticles composite latex particles, were successfully prepared. TEM, FTIR, thermogravimetric analysis, X‐ray photoelectron spectroscopy, spectrophotometry, and element analysis confirmed that well‐dispersed nanoparticles were encapsulated by the formed polymer, and the thickness of encapsulating polymer layer was in the range of 5–65 nm. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1478–1488, 2001     

Studies on electro‐optical properties of polymer matrix/LC/SiO2 nanoparticles composites

Polymer‐dispersed liquid crystal (PDLC) films were prepared by ultraviolet light‐induced polymerization of photopolymerizable monomers in nematic liquid crystal (LC)/monomers/SiO₂ nanoparticles composites, and the effect of SiO₂ nanoparticles on the electro‐optical properties of PDLC films was studied. The observed effect showed that by the adjustment of the SiO₂ nanoparticles content, the refractive index ratio of the LC and polymer could be modulated, and the electro‐optical properties of the polymer matrix/LC/SiO₂ nanoparticles composites could be optimized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Sulfonated polyetheretherketone/polypropylene polymer blends for the production of photoactive materials

Sulfonated polyetheretherketone (SPEEK) was synthesized via a mono‐substitution reaction of PEEK in concentrated sulphuric acid and was blended with polypropylene (PP) in 2–10%w/w concentration to be used for the production of photoactive thermoplastic products. SPEEK and SPEEK/PP blends were characterized using FTIR, DSC, TGA, NMR, rheology, SEM, and EPR. Under UV‐Vis irradiation, stable benzophenone ketyl (BPK) radicals were generated by hydrogen extraction from PP. By increasing the amount of SPEEK in the polymer blend a linear increase in the BPK radicals was achieved according to the EPR data. DSC and TGA tests indicated weaknesses in the thermal stability of SPEEK but according to the rheological tests this should not have a major effect on processabililty. The optimal amount of SPEEK in the blend was obtained at 5%w/w. This concentration provided a good compromise between radical concentration, material processability, and cost. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41509.     

Specific cationic photoinitiators for near UV and visible LEDs: Iodonium versus ferrocenium structures

Two iodonium salts based on a coumarin chromophore are investigated for polymerization upon light emitting diode irradiations (LEDs). They work as one‐component photoinitiators. They initiate the cationic polymerization of epoxides (under air) and vinylethers (laminate) upon exposure to violet LEDs (385 and 405 nm). Excellent polymerization profiles are recorded. Their efficiency is quite similar to that of a ferrocenium salt. Interpenetrating polymer networks can also be obtained through a concomitant cationic/radical photopolymerization of an epoxy/acrylate blend monomer. The light absorption properties of these new salts as well as the involved photochemical mechanisms are investigated for the first time through electron spin resonance, laser flash photolysis, steady state photolysis experiments. Molecular orbital calculations are also used to shed some light on the initiation mechanisms. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42759.     

Reactivity and efficiency of difunctional radical photoinitiators

Three difunctional cleavable photoinitiators based on the α‐hydroxyketone structure were tested in photopolymerization reactions with Fourier transform infrared spectroscopy. The excited‐state processes were investigated with time‐resolved laser absorption spectroscopy and laser‐induced photocalorimetry, which allowed the cleavage quantum yields to be determined and estimates of the triplet‐state lifetimes and interaction rate constants with a methacrylate monomer to be given. Modeling calculations helped to describe the ground‐state properties and showed that the difunctional photoinitiators exhibited different chromophoric groups than the corresponding monofunctional photoinitiator. An examination of the photochemical reactivity versus the practical efficiency observed in the polymerization showed that these difunctional photoinitiators exhibited better efficiency than the parent molecule, mainly because of their increased absorption properties. Their practical efficiency appeared to be better because of better light absorption when standard polychromatic light sources were used. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparison of two approaches to grafting hydrophilic polymer chains onto polysulfone films

To reduce the surface protein adsorption of polysulfone (PSf) film, we improved the hydrophilicity of this film by photochemical grafting of methoxypoly (ethylene glycol) (MPEG) derivatives on its surface. Grafting was achieved with both the simultaneous method and the sequential method. Surface analysis of the grafted film by X‐ray photoelectron spectroscopy (XPS) revealed that the PEG chains had successfully grafted onto the surface of the film. The grafting efficiencies by simultaneous and sequential methods were 20.8% and 10.2%, respectively. With an atomic force microscope (AFM), the surface topography of PEG‐grafted films by these two methods was compared. Static water contact angle measurement indicated that the surface hydrophilicity of the film had been improved. Protein adsorption measurement showed that the surface protein adsorption of the modified film was significantly reduced compared with that of the unmodified PSf film. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3818–3826, 2007     

自由基型光引发剂所用叔胺增感剂的研究概况

叔胺对提氢型光引发剂的增感作用使它在紫外固化领域中有重要的地位,本文介绍了增感剂的增感机理,并重点介绍了有关芳香族叔胺增感剂的种类、合成方法及研究进展。     

Kinetic analysis of solid‐state photodimerization reaction of photosensitive monomers and a polymer with cinnamoyl moieties

This work focused on the different kinetic behaviors in photodimerization between a low‐molecular‐weight molecule and a macromolecule, and the relationship between photodimerization and photo free radical polymerization. We have synthesized two monomers, one (M₁) containing a cinnamoyl moiety and another (M₂) containing both a cinnamoyl moiety and an acrylate moiety. Their chemical structures were confirmed by FTIR and ¹H‐NMR spectral analysis. Polymer (P₂) was obtained by free radical polymerization of acrylate moieties of M₂. Real‐time FTIR (RT‐FTIR) was used to analyze the kinetic effects of photoreaction. The results strongly suggest that cinnamoyl moieties did not undergo free radical polymerization under exposure of ultraviolet (UV) light. Additionally, the photodimerization of M₁ and P₂ has been confirmed by RT‐FTIR spectra, UV absorption, and transmittance spectra; and photodimerization of M₁ was also confirmed by solid‐state NMR spectra. The results show that this photoreaction of M₁ is much faster than that of M₂ and P₂. Wide angle X‐ray diffraction patterns have demonstrated their different molecular arrangements, which may be responsible for the difference in photodimerization reaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Near-infrared photorefractive polymer composites based on carbon nanotubes

A photorefractive effect at the wavelength of 1064 nm is demonstrated for a composite consisting of an aromatic polyimide and carbon single wall nanotubes. The two-beam gain coupling coefficient and the net gain coefficient are equal to 90 and 65 cm⁻¹, respectively, at 80 V/μm for a nanocomposite containing 0.25 wt% crude nanotube material. The refractive index modulation measured at E₀ = 50 V/μm is close to Δn = 0.004.     

Polymerization behavior of an organophosphorus monomer for use in dental restorative materials

Vibrational overtone activated polymerization of acrylonitrile (AN) has been demonstrated using two initiators, benzoyl peroxide (BP), and 2,2′‐(azobis)isobutyronitrile (AIBN). Excitation of the fifth vibrational overtone of the CH stretch of AIBN at 627 nm and BP at 604 nm initiates the reaction. Monomer conversions were monitored by a gravimetric method. In both cases, the wavelength selectivity was investigated by irradiating the monomer/initiator mixtures at the absorption maximum of the initiator, the absorption maximum of the monomer, and at a wavelength (580 nm for AN/AIBN and 625 nm for AN/BP) where neither the initiator nor the monomer absorbs light. For the AN/AIBN mixture, after 48 h the monomer conversion for the irradiation on the peak absorption of AIBN (627 nm) is about twice as large as the irradiation at 580 nm. For the AN/BP mixture, after 48 h the monomer conversion for the irradiation on the peak absorption of BP (604 nm) is about a factor of 2.2 larger than for the irradiation at 625 nm. The overall quantum yields of both polymerizations were estimated. After 48 h the overall quantum yield for the AN/AIBN mixture irradiated at the initiator absorption (Φ₆₂₇ = 21083) is about 10 times larger than for the sample irradiated at the pure monomer absorption (Φ₅₉₅ = 1942). For the AN/BP mixture, the 604 nm quantum yield (Φ₆₀₄ = 1096) is about 2.4 times larger than the 595 nm quantum yield (Φ₅₉₅ = 448). The influence of the initiator concentration is also presented. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 565–571, 2003     

麻纤维/聚合物复合材料

综述了近年来麻纤维/聚合物复合材料的研究进展,重点阐述了环境友好型复合材料的界面处理、成型工艺及性能研究.     

Water‐soluble and polymerizable thioxanthone photoinitiator containing imidazole

A novel free radical photoinitiator, 3‐allyl‐1‐[2‐hydroxy‐3‐(thioxanthen‐9‐one‐2‐yl)oxypropyl]imidazolium chloride ([AIPTX]Cl), is synthesized by the addition reaction of 2‐(2,3‐epoxy)propoxylthioxanthone (ETX) with a heterocyclic compound imidazole firstly, and the achieved intermediate 1‐[2‐hydroxy‐3‐(thioxanthen‐9‐one‐2‐yl)oxypropyl]imidazole (IPTX) is then reacted with allyl chloride. IPTX is chosen to evaluate the photoefficiency of [AIPTX]Cl. FTIR and ¹H‐NMR confirm the structures of [AIPTX]Cl and IPTX. UV‐Vis spectra of the two photoinitiators are similar and both exhibit the maximal absorption about 400 nm. Fluorescence spectra show [AIPTX]Cl/IMZ has slightly higher fluorescence intensity than IPTX system. Photopolymerization studies indicate that [AIPTX]Cl/IMZ is more efficient for the polymerization of water‐soluble monomer than IPTX. Moreover, due to its advantages of water solubility and polymerizability, [AIPTX]Cl is an environmental‐friendly photoinitiator and has potential for application in UV‐curing systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40659.     

Photochromic films prepared by solid state processing of disentangled ultrahigh molecular weight polyethylene and photochromic dyes composites

Disentangled ultrahigh molecular weight polyethylene (DPE) is a special grade of polyethylene (molecular weight, >10⁶ Da) which can be processed by an environment friendly solid state process on counter rotating two roll mill (TRM) below the melt temperature of the polymer. This unique processing property of DPE was utilized to develop smart DPE photochromic films. Photochromic dye like 'Spirooxazine' or 'Spiropyran' has been mixed with DPE resin powder prior to film formation without altering the DPE properties. These films could change their optical appearances on exposure to UV-light of wavelength 365 nm and the color change phenomenon of the films could also be replicated by sunlight. The color change observed is found to be reversible, that is, films could return to colorless form either spontaneously in dark or by thermal stimuli. Such smart property was imparted to DPE even at very low concentration (2,000 ppm) of photochromic dyes. Spectrophotometric studies were used to measure the rate of forward reaction with UV radiation and the rate of backward reaction in dark. In fact, DPE powder and photochromic dye composite was used to produce the compression molded disc to understand the color change phenomena. Moreover, it was observed that the photo-degradation rate of dye, could be retarded ~30% by using amphoteric Zinc phthalate salt. TGA and DSC studies confirmed that the characteristics of DPE film remained almost unaltered even after with preparation of film photochromic dyes.     

A new modified silicone–TiO2 polymer composite film and its photocatalytic degradation

The photodegradation of the silicone surfactant–TiO₂ composite films was characterized by FTIR, Raman spectroscopy, and scanning electron microscope. After photocatalytic degradation, the FTIR Si? O? Si peak intensity of the composite film remained unchanged, implying no cleavage of Si? O? Si bond. The above Si? O? Si peak intensity is sensitive to the polyoxyethylene chain length of the composite. The PEG10000‐silicone composite is more resistant to photodegradation than those composites with lower molecular weight of constituent PEGs. The wetting rates of the silicone surfactant–TiO₂ composites showed that modified silicone composite films exhibited hydrophobic nature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3341–3344, 2006