Ethyl 4-dimethylaminobenzoate Research Articles

Tris(trimethylsilyl)silane as a co-initiator for dental adhesive: Photo-polymerization kinetics and dynamic mechanical property

ObjectivesThe purpose of this study was to evaluate the polymerization behavior of a model dentin adhesive with tris(trimethylsilyl)silane (TTMSS) as a co-initiator, and to investigate the polymerization kinetics and mechanical properties of copolymers in dry and wet conditions. MethodsA co-monomer mixture based on HEMA/BisGMA (45/55, w/w) was used as a model dentin adhesive. The photoinitiator system included camphorquinone (CQ) as the photosensitizer and the co-initiator was ethyl-4-(dimethylamino) benzoate (EDMAB) or TTMSS. Iodonium salt, diphenyliodonium hexafluorophosphate (DPIHP) serving as a catalyst, was selectively added into the adhesive formulations. The control and the experimental formulations were characterized with regard to the degree of conversion (DC) and dynamic mechanical properties under dry and wet conditions. ResultsIn two-component photoinitiator system (CQ/TTMSS), with an increase of TTMSS concentration, the polymerization rate and DC of CC double bond increased, and showed a dependence on the irradiation time and curing light intensity. The copolymers that contained the three-component photoinitiator system (CQ/TTMSS/DPIHP) showed similar dynamic mechanical properties, under both dry and wet conditions, to the EDMAB-containing system. SignificanceThe DC of formulations using TTMSS as co-initiator showed a strong dependence on irradiation time. With the addition of TTMSS, the maximum polymerization rate can be adjusted and the network structure became more homogenous. The results indicated that the TTMSS could be used as a substitute for amine-type co-initiator in visible-light induced free radical polymerization of methacrylate-based dentin adhesives.

Relative photon absorption determination and the influence of photoinitiator system and water content on C=C conversion, water sorption/solubility of experimental self-etch adhesives

The present study aimed to determine the influence of photoinitiator/co-initiator system and the water content on polymerization efficiency, water sorption and solubility of experimental self-etch adhesives; as well as to understand the relation between photoinitiators and the curing unit on the resultant properties. Experimental adhesive formulations were formulated by mixing bis-2-methacyloyloxy-ethyl phosphate (2MP, Sigma Aldrich, USA) and 2-hydroxyethylmethacrylate (HEMA, Esstech Inc., USA) in equal parts by weight. Four photoinitiators were used: camphorquinone (CQ), phenantrequinone (PQ), trimethylbenzoyl-diphenyl-phosphine oxide (TPO) and bisacyl-phosphine oxide (BAPO). The tertiary amine ethyl-4-dimethylaminobenzoate (EDMAB) and the salt diphenyliodonium hexafluorphosphate (DPI) were tested as co-initiators. The following groups were tested: CQ+EDMAB, CQ+EDMAB+DEPI, PQ, PQ+EDMAB, PQ+DPI, PQ+EDMAB+DPI, TPO TPO+DPI, BAPO and BAPO+DPI. Materials were tested both without and with the addition of 10wt% of deuterium water (D2O). Photoinitiator absorption and the light-curing emission spectra were determined with a spectrophotometer to calculate the relative photons absorption (RPabs). Degree of conversion was obtained with Fourier-transformed infrared spectroscopy (FTIR/ATR). Water sorption and solubility were determined after successive weighting procedures. Results were analyzed by two-way analysis of variance (ANOVA) followed by Tukey׳s post-hoc test (α=0.05). PQ exhibited the highest RPabs values (334.9), followed by CQ (52.8), BAPO (33.7) and TPO (8.4). TPO-based material presented the highest DC in the neat state. Considering the formulations with water addition, TPO- and BAPO-based materials presented the highest values, whereas CQ- and PQ-based ones produced conversion values below 4.6. TPO- and BAPO-based materials presented superior performance than CQ- and PQ-based ones for water sorption and solubility. It was possible to conclude that self-etch adhesives ability to polymerize was not only dependent on the relation between light and photoinitiators spectra, but also individual characteristics of free radicals development and that groups formulated with TPO and BAPO presented superior properties as those formulated with CQ and PQ.

Synthesis and properties of a low-viscosity UV-curable oligomer for three-dimensional printing

A novel photosensitive low-viscosity epoxy acrylate resin was synthesized by utilizing polyethylene glycol diglycidyl ether (PEGGE) and acrylic acid (AA) as starting materials. The structure of polyethylene glycol diglycidyl ether diacrylate (PEGGEA) was characterized by Fourier transform infrared spectroscopy (FTIR). 2-Isopropyl thioxanthone (ITX), ethyl 4-(dimethylamino) benzoate (EDAB) and 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone (369) as photoinitiators and trihydroxymethyl propane triacrylate (TMPTA) as monomer were mixed with PEGGEA to prepare a kind of UV-curable resins, which may be utilized to boost the resin curing under UV light. The UV-curing properties and the thermal stability of the prepared resins with different contents of oligomer were investigated using FTIR-attenuated total reflection (ATR) spectroscopy and TGA. The viscosity of the oligomers and the mechanical properties of the cured resins were also studied. The results showed that the content of oligomer will affect the UV-curing properties and the thermal stability of the UV-curing resins. The viscosity of the prepared UV-curing resins was less than 200 mPa s at 25 °C, and the hardness of cured resins was high than 6H, which could meet the requirements for three-dimensional printing (3DP).

Photopolymerization of pyrrole/methacrylate mixtures using α-cleavage type photoinitiators in combination with iodonium salt

Hybrid systems formulated with pyrrole and methacrylate monomers were photopolymerized with both UV (λ=365nm) and visible (λ=470nm) light. It is known that conducting polymers produced by electrochemical or chemical synthesis are intractable solids or powders which display poor mechanical properties and low processability. An advantage of the photopolymerization process is that it allows processability and mechanical properties of final polymers to be optimized by incorporating flexibilizers and different additives into photopolymerizable formulations. Mixtures pyrrole/methacrylate were photoactivated with the iodonium salt p-(octyloxyphenyl)phenyliodonium hexafluoroantimonate (Ph2ISbF6), in combination with 2,2-dimethoxy-2-phenylacetophenone (DMPA), 2-methoxy-2-phenylacetophenone (BZME) or the pair camphorquinone (CQ)/ethyl-4-dimethylamino benzoate (EDMAB). The Ph2ISbF6 in combination with DMPA or BZME was an efficient photoinitiator system under irradiation at 365nm. Conversely, in mixtures photoactivated with Ph2ISbF6/CQ/EDMAB the polymerization of both pyrrole and methacrylate was comparatively slow. Microscopy studies revealed the absence of phase separation indicating that the mixtures pyrrole/methacrylate resulted in the formation of an interpenetrating polymer network. The electrical conductivity of the hybrid polymers increased markedly with the amount of polypyrrole as a result of the formation of a conducting polymer network in the insulating BisEMA matrix.

Novel dental composite material reinforced with silane functionalized microsized gypsum filler particles

Gypsum has been recognized as acceptable for human consumption as a dietary source of calcium. During contact with teeth, it releases Ca2+ ions needed for remineralization of tooth tissue, and therefore based on the concept of remineralization, gypsum may be a strategic additive for dental restorative materials. Hence, the objective of this study was to develop and characterize a novel dental material reinforced with different weight fraction of micro sized gypsum filler particle. A novel composite material was fabricated using conventional resin matrix consisting of Bisphenol‐A glycidyl methacrylate (Bis‐GMA), tri‐ethylene glycol dimethacrylate (TEGDMA), camphorquinone (CQ) and ethyl 4 dimethyl amino benzoate (EDMAB). Four different compositions were prepared by reinforcing different weight percentage (0–3 wt%) of silane functionalized micro sized gypsum particle. Fourier Transformed Infrared spectroscopy (FT‐IR), Transmission Electron Microscope (TEM) and Thermogravimetric Analysis (TGA) of silane treated filler were used to study the coupling phenomena between filler and resin. Polymerization shrinkage of composites was evaluated using specific gravity method. The Dynamic Mechanical Analysis (DMA) result revealed that the Glass transition temperature was found to be decreased by 15°C compared to unfilled composite. It was also found that the 2 wt% gypsum content recorded the highest value of storage modulus. Simultaneous Thermal Analysis (STA) result revealed that 2 wt% gypsum filled dental composite exhibited maximum thermal stability. The novel dental material exhibited better physical, optical, mechanical, thermal properties and lowest polymerization shrinkage with maximum conversion. POLYM. COMPOS., 38:404–415, 2017. © 2015 Society of Plastics Engineers

Development of methacrylate/silorane hybrid monomer system: Relationship between photopolymerization behavior and dynamic mechanical properties.

Resin chemistries for dental composite are evolving as noted by the introduction of silorane-based composites in 2007. This shift in the landscape from methacrylate-based composites has fueled the quest for versatile methacrylate-silorane adhesives. The objective of this study was to evaluate the polymerization behavior and structure/property relationships of methacrylate-silorane hybrid systems. Amine compound ethyl-4-(dimethylamino) benzoate (EDMAB) or silane compound tris(trimethylsilyl) silane (TTMSS) was selected as coinitiators. The mechanical properties of the copolymer were improved significantly at low concentrations (15, 25, or 35 wt %) of silorane when EDMAB was used as coinitiator. The rubbery moduli of these experimental copolymers were increased by up to 260%, compared with that of the control (30.8 ± 1.9 MPa). Visible phase separation appeared in these formulations if the silorane concentrations in the formulations were 50-75 wt %. The use of TTMSS as coinitiator decreased the phase separation, but there was a concomitant decrease in mechanical properties. In the neat methacrylate formulations, the maximum rates of free-radical polymerization with EDMAB or TTMSS were 0.28 or 0.06 s(-1) , respectively. In the neat silorane resin, the maximum rates of cationic ring-opening polymerization with EDMAB or TTMSS were 0.056 or 0.087 s(-1) , respectively. The phase separation phenomenon may be attributed to differences in the rates of free-radical polymerization of methacrylates and cationic ring-opening polymerization of silorane. In the hybrid systems, free-radical polymerization initiated with EDMAB led to higher crosslink density and better mechanical properties under dry/wet conditions. These beneficial effects were, however, associated with an increase in heterogeneity in the network structure. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 841-852, 2016.

Physical and thermo-mechanical characterizations of resin-based dental composite reinforced with silane-modified nanoalumina filler particle

The aim of this study was to analyze the effect of adding different weight percentages of nanoalumina particles on mechanical properties of resin-based dental composite materials. The composite specimens were prepared by dispersion of different percentage weight fractions (0 wt%, 1 wt%, 2 wt% and 3 wt%) of silane-modified nanoalumina filler in a monomer system containing 50% bisphenol-A glycidyl methacrylate, 49% tri-ethylene glycol dimethacrylate, 0.2% Camphorquinone and 0.8% Ethyl 4-dimethylaminobenzoate. The filler particle before and after silane treatment was characterized using Fourier-transform infrared spectroscopy and transmission electron microscopy. The presence of C = O bond and Si–O–Si linkage between the monomer and filler was clearly indicated. Mechanical behavior of the light-cured samples was evaluated using compressive strength test, three-point flexural strength test, Vicker Micro hardness tests, dynamic mechanical analysis and simultaneous thermal analysis. The results indicated a more than 16% increase in the compressive strength in the samples containing nanoalumina filler particles. Vickers hardness of composite was increased by approximately 28% with respect to unfilled composite. The flexural modulus of composite mixed with alumina nanoparticles was increased from 1.7 to 5.1 GPa, while the values of composite were slightly decreased from 84.5 to 59.5 MPa. The dynamic mechanical analysis result revealed that the glass transition temperature was found to be increased by 30 ℃ compared to unfilled composite. It was also found that the 1 wt% nanoalumina content recorded the highest value of storage modulus. The weight loss profile and thermal stability from thermogravimetric analysis results revealed that the composite filled with 2 wt% nanoalumina content exhibited maximum thermal stability.

Synthesis, characterization, and photocuring of siloxane-oxirane monomers

The aim of this study was to synthesize, characterize, and evaluate alternative monomers for use in dentistry. Three siloxane-oxirane low-shrinkage monomers were synthesized, and the products’ conversion was followed by Fourier transform-infrared spectroscopy. The products obtained were characterized by 1H and 13C NMR and evaluated for viscosity and a refractive index. The polymerization was evaluated by formulating two experimental photoinitiation systems, which varied for the presence of 1,2 ethanediol. A ternary system with camphorquinone (CQ), ethyl 4-dimethylaminobenzoate (EDAB), and diphenyliodonium hexafluorphosphate (DPI) was used as control. The degree of conversion was assessed by differential scanning calorimetry (DSC). The NMR confirmed the synthesis success with 75, 87, and 55% yields for the monomers synthesized. The viscosity and the refractive index of the monomers showed favorable rheological and physical behaviors for application in dentistry. Moreover, the presence of 1,2-ethanediol increased the degree of conversion of the siloxane-oxirane monomers. This study showed a simple and effective way to synthesize siloxane-oxirane monomers with a high potential for application in dental materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1728–1733

Polymerization Behavior of Hydrophilic-Rich Phase of Dentin Adhesive

The 2-fold objectives of this study were 1) to understand whether model hydrophobic- and hydrophilic-rich phase mimics of dentin adhesive polymerize similarly and 2) to determine which factor, the dimethacrylate component, bisphenol A glycerolate dimethacrylate (BisGMA) or photoinitiator concentration, has greater influence on the polymerization of the hydrophilic-rich phase mimic. Current dentin adhesives are sensitive to moisture, as evidenced by nanoleakage in the hybrid layer and phase separation into hydrophobic- and hydrophilic-rich phases. Phase separation leads to limited availability of the cross-linkable dimethacrylate monomer and hydrophobic photoinitiators within the hydrophilic-rich phase. Model hydrophobic-rich phase was prepared as a single-phase solution by adding maximum wt% deuterium oxide (D2O) to HEMA/BisGMA neat resins containing 45 wt% 2-hydroxyethyl methacrylate (HEMA). Mimics of the hydrophilic-rich phase were prepared similarly but using HEMA/BisGMA neat resins containing 95, 99, 99.5, and 100 wt% HEMA. The hydrophilic-rich mimics were prepared with standard or reduced photoinitiator content. The photoinitiator systems were camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDMAB) with or without [3-(3, 4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-2-hydroxypropyl]trimethylammonium chloride (QTX). The polymerization kinetics was monitored using a Fourier transform infrared spectrophotometer with a time-resolved collection mode. The hydrophobic-rich phase exhibited a significantly higher polymerization rate compared with the hydrophilic-rich phase. Postpolymerization resulting in the secondary rate maxima was observed for the hydrophilic-rich mimic. The hydrophilic-rich mimics with standard photoinitiator concentration but varying cross-linker (BisGMA) content showed postpolymerization and a substantial degree of conversion. In contrast, the corresponding formulations with reduced photoinitiator concentrations exhibited lower polymerization and inhibition/delay of postpolymerization within 2 h. Under conditions relevant to the wet, oral environment, photoinitiator content plays an important role in the polymerization of the hydrophilic-rich phase mimic. Since the hydrophilic-rich phase is primarily water and monomethacrylate monomer (e.g., HEMA as determined previously), substantial polymerization is important to limit the potential toxic response from HEMA leaching into the surrounding tissues.

Efficient visible photoinitiator containing linked dye-coinitiator and iodonium salt for free radical polymerization

Abstract Dye-linked initiators consisting of erythrosine B as a chromophore and ethyl 4-dimethylaminobenzoate as an electron donor linked by a different number of methylene units were prepared to achieve efficient photoinitiators of free radical polymerization in a visible-light region. The relative photoinitiating efficiencies of novel photoinitiators in photopolymerization of acrylates were evaluated. The results showed that the photoinitiating system composed of the dye-linked dyad with short methylene unit chain and diphenyliodonium salt exhibited a remarkable increase in the photoinitiation ability compared to unlinked three-component system. The enhancement mechanism aroused by the onium salt was investigated. These results showed that the excellent initiating efficiency of this system could be attributed to the favorable intramolecular photoinduced electron transfer and the close distance between reaction components caused by electrostatic interactions. This result demonstrated the importance and potential of the linked photoinitiator in the design of new efficient photoinitiators.

Physical-mechanical properties of Bis-EMA based root canal sealer with different fillers addition.

Aim:To evaluate influence of three different filler particles on an experimental Bisphenol A ethoxylated dimethacrylate (Bis-EMA) based root filling material.Materials and Methods:Resin-based endodontic sealers were produced using Bis-EMA, camphorquinone, ethyl 4-dimethylaminobenzoate (EDAB), N, N-dihydroxyethyl-p-toluidine (DHEPT), butylated hydroxytoluene (BHT), and benzoyl peroxide. The experimental groups were formulated adding 10, 20, 30, 40, and 50% of calcium tungstate (CaWO4), ytterbium trifluoride(YbF3), and tantalum oxide(Ta2O5). Flow, thickness, and radiopacity tests were conducted in accordance with ISO 6876. Sorption and solubility (SL) tests were conducted in accordance with ISO 4049, pH was measured with a pH meter, and degree of conversion (DC) was evaluated with Fourier transform infrared spectroscopy (FTIR). For radiopacity, two-way analysis of variance (ANOVA) and Tukey's multiple comparison test was performed. For DC analysis, one-way ANOVA and Tukey's multiple comparison test was performed. All statistical analyses were performed with a significance level of 5%.Results:All groups showed lower flow with increased filler concentration. All groups showed film thickness values lower than 50μm, as ISO recommends, except CaWO450% group (76.7μm). pH values varied from 5.95 (± 0.07) in YbF340% group to 6.90 (± 0.07) in Ta2O540% group. In the radiopacity test, YbF330%, Ta2O540%, and Ta2O550% groups showed no statistical significant difference to 3mmAl. Ta2O5 and YbF3 groups in 10, 20, and 30% concentrations presented sorption and SL values as ISOrecommendation. Addition ofTa2O5 and CaWO4 decreased DC after 14 days. YbF3 addition showed no difference in DC from control group.Conclusion:YbF3 filler addition promoted higher properties compared to CaWO4 and Ta2O5 on Bis-EMA based root canal sealer.

Low-temperature heat capacities and thermodynamic properties of ethyl 4-dimethylaminobenzoate (C11H15NO2)

Molar heat capacities of ethyl 4-dimethylaminobenzoate were measured by a high precision automated adiabatic calorimeter over the temperature range from 79 to 397 K. The melting temperature, the molar enthalpy and entropy of fusion were determined to be (336.818 ± 0.017) K, (20.761 ± 0.345) kJ mol−1 and (61.64 ± 1.03) J K−1 mol−1. It has a great potential in the use of the substance as solid–liquid phase change material based on large enthalpy of solid–liquid phase transition and moderate melting temperature. The thermodynamic functions (HT−H298.15 K) and (ST−S298.15 K) were calculated in the temperature range from 80 to 400 K with the interval of 5 K. The mass fraction purity of the sample was determined to be (1−N) = 0.99514 (mol fraction) by the fractional melting method. The constant-volume energy and standard molar enthalpy of combustion were determined, ΔcU (C11H15NO2, s) = −(6,161.73 ± 5.19) kJ mol−1 and Δc\( H_{\text{m}}^{0} \) (C11H15NO2, s) = −(6,167.31 ± 5.19) kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. At last, the standard molar enthalpy of formation was derived, Δf\( H_{\text{m}}^{0} \) (C11H15NO2, s) = −(305.03 ± 6.92) kJ mol−1.

BAPO as an alternative photoinitiator for the radical polymerization of dental resins

ObjectivesThis study evaluated the performance of phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO) as an alternative photoinitiator in the polymerization kinetics (PK), flexural strength (σ) and elastic modulus (E) of a model dental resin. MethodsA monomer mixture based on Bis-GMA and TEGDMA was used as model dental resin. Initially a screening was performed to evaluate BAPO concentrations (0.125, 0.25, 0.50, 1, 2, and 4mol%). Photoinitiator systems were formed with the combination of camphorquinone (CQ), ethyl-dimethylamino benzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), and BAPO. Groups with unitary photoinitiator systems (BAPO and CQ), binary (BAPO+EDAB, BAPO+DPIHFP and CQ+EDAB), ternary (BAPO+CQ+EDAB, BAPO+CQ+DPIHFP, BAPO+EDAB+DPIHFP and CQ+EDAB+DPIHFP) and quaternary (BAPO+CQ+EDAB+DPIHFP) were formulated for evaluation. Real-time Fourier transform infrared spectroscopy was used to investigate the PK and test mini-bending to evaluate σ and E. ResultsWhen only CQ was used, a slow polymerization reaction was observed and a lower monomer conversion. When only BAPO was used as photoinitiator an increase in the polymerization rate was observed and conversion was higher than CQ+EDAB. The ternary system (BAPO+EDAB+DPIHFP) showed the highest polymerization and conversion rate, in short photo-activation time. SignificanceBAPO it is a potential photoinitiator for the photopolymerization of dental materials.

Degree of conversion and monomer elution of CQ/amine and TPO adhesives

ObjectiveTo evaluate the effect of photo-initiator on the degree of conversion (DC) and elution of Bis-GMA and HEMA for 8 one-step adhesive formulations. MethodsWe used Scotchbond Universal (‘SBU-CQ/amine_4.0’, 3M ESPE), containing about 2wt% camphorquinone (CQ) and 2wt% ethyl-4-dimethylamino benzoate (EDMAB), an experimental ‘SBU-TPO_2.1’ version, containing 2.1wt% diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and 6 experimental LUB adhesives (Kuraray Noritake), namely ‘LUB-CQ/amine_0.7’, ‘LUB-CQ/amine_1.4’, ‘LUB-CQ/amine_4.0’, ‘LUB-TPO_0.35’, ‘LUB-TPO_0.7’ and ‘LUB-TPO_2.0’, respectively containing 0.35wt% CQ and 0.35wt% EDMAB, 0.7wt% CQ and 0.7wt% EDMAB, 2.0wt% CQ and 2.0wt% EDMAB, 0.35wt% TPO, 0.7wt% TPO, and 2.0wt% TPO. DC was measured using micro-Raman spectroscopy. Additional specimens were immersed in ethanol for 24h to determine the elution of Bis-GMA and HEMA using HPLC. ResultsDC of the respective SBU and LUB adhesives was alike at high photo-initiator concentration. At low concentration, TPO was significantly more efficient than CQ/amine (LUB adhesives only). A statistically significant positive photo-initiator concentration effect on DC was noted for both CQ/amine and TPO (LUB adhesives only). A statistically significant inverse photo-initiator concentration effect on HEMA elution was noted for both the CQ/amine- and TPO-containing LUB adhesives. A significantly strong correlation was found between DC and Bis-GMA elution (R2=0.744, p=0.026), and between DC and HEMA elution (R2=0.913, p=0.002) for the LUB adhesives. SignificanceThe photo-initiator kind and concentration affect DC and the Bis-GMA/HEMA elution. TPO can be used as an alternative photo-initiator for CQ/amine.

Evaluation of the migration of 15 photo-initiators from cardboard packaging into Tenax® using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)

Photo-initiators are widely used to cure ink on packaging materials used in food applications such as plastic films or cartonboards. In migration studies, food simulants are very often used to simulate food, like Tenax®, which is the simulant for dry foodstuffs. In this paper a fast and reliable confirmation method for the determination of the following photo-initiators in Tenax® is described: benzophenone (BP), 4,4´-bis(diethylamino)benzophenone (DEAB), 2-chloro-9H-thioxanthen-9-one (CTX), 1-chloro-4-propoxy-9H-thioxanthen-9-one (CPTX), 2,4-diethyl-9H-thioxanthen-9-one (DETX), 2,2-dimethoxy-2-phenyl acetophenone (DMPA), 4-(dimethylamino)benzophenone (DMBP), 2-ethylanthraquinone (EA), ethyl-4-dimethylaminobenzoate (EDMAB), 1-hydroxylcyclohexyl phenyl ketone (HCPK), 2-hydroxy-4´-(2-hydroxyethoxy)-2-methylpropiophenone (HMMP), 2-isopropyl-9H-thioxanthen-9-one (ITX), 4-methylbenzophenone (MBP), Michler’s ketone (MK), and 4-phenylbenzophenone (PBZ). After the migration study was completed, the simulant Tenax® was extracted using acetonitrile, followed by analysis on ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Quantification was carried out using benzophenone-d10 (BP-d10) as internal standard. The presented method is validated in terms of matrix effect, specificity, linearity, recovery, precision and sensitivity, showing the method can detect all photo-initiators at very low concentrations (LOD < 0.125 µg g–1 for all substances). Finally, the procedure was applied to real samples, proving the capabilities of the presented method.

Hydroxyapatite induces spontaneous polymerization of model self-etch dental adhesives

The objective of this study is to report for the first time the spontaneous polymerization phenomenon of self-etch dental adhesives induced by hydroxylapatite (HAp). Model self-etch adhesives were prepared by using a monomer mixture of bis[2-(methacryloyloxy)ethyl] phosphate (2MP) with 2-hydroxyethyl methacrylate (HEMA). The initiator system consisted of camphorquinone (CQ, 0.022mmol/g) and ethyl 4-dimethylaminobenzoate (4E, 0.022–0.088mmol/g). HAp (2–8wt.%) was added to the neat model adhesive. In a dark environment, the polymerization was monitored in-situ using ATR/FT-IR, and the mechanical properties of the polymerized adhesives were evaluated using nanoindentation technique. Results indicated that spontaneous polymerization was not observed in the absence of HAp. However, as different amounts of HAp were incorporated into the adhesives, spontaneous polymerization was induced. Higher HAp content led to higher degree of conversion (DC), higher rate of polymerization (RP) and shorter induction period (IP). In addition, higher 4E content also elevated DC and RP and reduced IP of the adhesives. Nanoindentation result suggested that the Young's modulus of the polymerized adhesives showed similar dependence on HAp and 4E contents. In summary, interaction with HAp could induce spontaneous polymerization of the model self-etch adhesives. This result provides important information for understanding the initiation mechanism of the self-etch adhesives, and may be of clinical significance to strengthen the adhesive/dentin interface based on the finding.

1,3-Diethyl-2-thiobarbituric acid as an alternative coinitiator for acidic photopolymerizable dental materials

The ethyl-4-dimethylaminobenzoate (EDAB) is widely used as a coinitiator of the camphorquinone (CQ), but in acidic circumstances it might present some instability, reducing the polymerization efficiency of the material. Considering this, new coinitiators are being evaluated. Hence, this study evaluated the kinetic of polymerization (KP), the degree of conversion (DC), and the rate of polymerization (RP ) of experimental resin adhesives containing 1,3-diethyl-2-thiobarbituric acid (TBA) as a coinitiator of the CQ. The experimental monomeric blend was prepared with bisphenol A glycidyl dimethacrylate, 2-hydroxyethyl methacrylate, and acidic monomers. CQ was added at 1 mol % as photoinitiator. Six groups were formulated: four containing concentrations of 0.1, 0.5, 1, and 2 mol % of TBA, one without coinitiator, and the last one containing 1 mol % of EDAB (control group). The KP and the RP were performed using real-time Fourier Transform infrared spectroscopy. The group without coinitiator has not formed a polymer, whereas the addition of TBA resulted in the conversion of monomers in polymer. The DC of the adhesives was as higher as the increase in the TBA content. The group with 2 mol % of TBA presented improved DC and reactivity (RP ) than the other groups and the control one. Hence, the TBA has performed as a coinitiator of the CQ for the radical polymerization of methacrylate resin adhesives and it has improved the DC and the reactivity of the materials. Thus, it is a potential coinitiator for the photopolymerization of dental materials.

Visible light polymerization of epoxy monomers using an iodonium salt with camphorquinone/ethyl-4-dimethyl aminobenzoate

A visible light initiator system for the photoinduced cationic polymerization of epoxy monomers is reported. The system consists of camphorquinone (CQ) in combination with ethyl-4-dimethyl aminobenzoate (EDMAB) and a diaryliodonium salt (Ph2ISbF6.) The three-component system efficiently photoinitiates the polymerization of monomers containing an epoxycyclohexane group, 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexane carboxylate (UVR) and 1,3-bis(3,4-epoxycyclohexyl-2-ethyl),1,1,3,3-tetramethyldisiloxane (SIB), under irradiation with blue light (λ = 467 nm). Very rapid photopolymerization resulted from irradiation of SIB containing Ph2ISbF6 in combination with CQ and better results were obtained in the presence of EDMAB. On the other hand, no polymerization was detected after irradiation of UVR photoactivated with Ph2ISbF6 and CQ. However, this monomer polymerized readily and to high conversion when EDMAB was present. Moreover, almost complete conversion of UVR occurs in the absence of external heating. The polymer resulting from UVR displayed higher values of compressive and flexural properties than the polymer prepared from SIB. This is explained in terms of a higher density of crosslinking points in UVR which is accompanied by a lower content of non-reacted monomer; this has a plasticizing effect on the hardened material. © 2013 Society of Chemical Industry

Determination of ten photoinitiators in fruit juices and tea beverages by solid-phase micro-extraction coupled with gas chromatography/mass spectrometry

A method for the determination of ten photoinitiators (PIs), benzophenone, ethyl 4-dimethylaminobenzoate, 1-hydroxycyclohexyl-phenylketone, 4-methylbenzophenone, 2-ethylhexyl-4-dimethylaminobenzoate, 4-chlorobenzophenone, 2-chlorothioxanthone, 2-isopropylthio-xanthone, 2,2-dimethoxy-2-phenylacetophenone, methyl 2-benzoylbenzoate, in 13 kinds of fruit juice and 3 kinds of tea beverage has been established, using solid-phase micro-extraction (SPME) combined with chromatography/mass spectrometry (GC/MS). At first, the major factors of SPME, extraction time and temperature, were studied through orthogonal experiment. Then the optimal operation conditions were obtained via the refinement of various factors. After the sample was extracted by SPME, it was desorbed for target analytes in sampling inlet for 3 min, and separated on an HP-5MS column, then detected by MS in selected ion monitoring mode, and quantified through calibration curve. The working curves were obtained using sample matrix in order to eliminate the matrix interference. The linear range was from 0.3 microg/L to 60 microg/L and the detection limit range was from 3 ng/L to 16 ng/L. The samples were determined five times with four different spiked levels individually and the relative standard deviations of all the samples were less than 14.5%. This determination method was applied in 16 kinds of packed beverages with different brands and different species. Benzophenone had been detected from all the samples. 4-Methylbenzophenone, 2-ethylhexyl-4-dimethylaminobenzoate, 2-isopropylthioxanthone, 1-hydroxycyclohexyl-phenylketone and 2-chlorothioxanthone had been detected from a portion of samples. Simultaneous determination was achieved for the ten PIs. These results provide a reference to determine the PIs migrated from packing materials in beverage. This method is simple, high sensitive and non-polluting.

Determination of the migration of seven photoinitiators in food packaging materials into aqueous solvent

The quantity of photoinitiators (PIs) migrated into hydrosoluble foods from packaging materials is usually very small. It is hardly detectable by using the current methods. For this reason, the article describes a new effective method for detecting the migration of PIs. In this method, the migration experiment was done in aqueous food simulation. After the PIs in printing inks used in food contact materials were extracted from the solution via solid-phase microextraction (SPME) using 65 microm polydimethylsiloxane/divinylbenzene (PDMS-DVB)-coated fiber, their migration amounts were determined by gas chromatography-mass spectrometry (GC-MS) in the selected ion monitoring mode (SIM). The PIs determined by SPME/GC-MS were benzophenone (BP), 1-hydroxycyclohexyl-phenylketone (CPK), ethyl-4-dimethyl-aminobenzoate (EDMAB), 4-methylbenzophenone (4-MBP), 2, 2-dimethoxy-2-phenylacetophenone (2,2-DMPA), methyl 2-benzoylbenzoate (OMBB) and 2-ethylhexyl-4-dimethyl-aminobenzoate (EHDAB). The limits of detection (S/N = 3) were between 0.0012 and 0.0069 microg/L. The linearity ranged from 0.03 to 1.0 microg/L (r2 > 0.9909). The recoveries were in the range from 70.8% to 112.0% (n = 3) with the relative standard deviations no more than 14.0%. Twenty samples were tested by using this developed method. The analytical results showed that BP was detected in all samples, and the migration amounts of BP were from 0.002 to 0.074 microg/dm2; 4-MBP was detected in ten samples, and the migration amounts of 4-MBP were from 0.006 to 0.019 microg/dm2; CPK was detected in three samples, and its amounts were 0.005, 0.005, 0.007 microg/dm2; 2,2-DMPA was detected as 0.009 microg/dm2 in one sample. The determination of real samples showed this method is feasible. The method is sensitive, simple and free from organic solvents. It could make reference to migrating determination of PIs in printing inks on food packaging surface.