Photopolymerization Rate Research Articles

Reduced polymerization stress of MAPO-containing resin composites with increased curing speed, degree of conversion and mechanical properties

ObjectivesThe degree and rate of photopolymerization in resin-based dental composites will significantly affect polymer network formation and resultant material properties that may determine their clinical success. This study investigates the mechanical properties, the generation of stress from polymerization, tooth cusp deflection and marginal integrity of experimental resin composites that contain different photoinitiators. MethodsExperimental light-activated resin composites (60vol% particulate filled in 50/50mass% bis-GMA/TEGDMA) were formulated using a monoacylphosphine oxide (MAPO) photoinitiator and compared with a conventional camphoroquinone (CQ)-based system. Similar radiant exposure was used (18Jcm−2) for polymerization of each material although the curing protocol was varied (400mWcm−2 for 45s, 1500mWcm−2 for 12s and 3000mWcm−2 for 6s). Degree and rate of polymerization was calculated in real-time by near infrared spectroscopy and the generation of stress throughout polymerization measured using a cantilever beam method. Flexural strength and modulus were acquired by three-point bend tests. Standardized cavities in extract pre-molar teeth were restored with each material, the total cuspal deflection measured and post-placement marginal integrity between the tooth and restoration recorded. ResultsGenerally, MAPO- exhibited a significantly higher degree of conversion (72±0.8 to 82±0.5%) compared with CQ-based materials (39±0.7 to 65±1.6%) regardless of curing protocol (p<0.05) and MAPO-based materials exhibited less difference in conversion between curing protocols. CQ-based materials exhibited between ∼85 and 95% of the maximum rate of polymerization at <15% conversion, whereas MAPO-based RBCs did not approach the maximum rate until >50% conversion. Higher irradiance polymerization had a significant deleterious effect on the mechanical properties of CQ-based materials (p<0.05) whereas MAPO-based materials exhibited increased strength and modulus and were less affected by the curing method. Total cuspal deflection in restored extracted teeth was higher for CQ- compared with MAPO-based materials cured at the lowest irradiance curing protocol (12.9±4.0 and 8.3±1.5μm) and similar at 3000mWcm−1 for 6s (10.1±3.5 and 9.0±1.5μm). A significant decrease in marginal integrity was observed for CQ-based RBCs cured at high irradiance for short exposure time compared with that of the MAPO-based RBC cured using a similar protocol (p=0.037). SignificancePolymer network formation dictates the final properties of the set composite and the use MAPO photoinitiators may provide an effective restorative material that exhibits higher curing speeds, increased degree of conversion, strength and modulus without compromise in terms of polymerization stress and marginal integrity between tooth and restoration.

Photoinitiation of methacrylate polymerization with an o-benzoquinone-amine system

The kinetic features of the photopolymerization of mono- and dimethacrylates in the presence of the binary initiating system comprising a substituted o-benzoquinone and a tertiary amine under the action of visible light are studied. In the case of methyl methacrylate, the limiting conversion of the monomer does not exceed 10%. The photopolymerization of oligo(ester methacrylates) yields a polymer glass with a monomer conversion of 60–90%. As is shown for a series of seven o-benzoquinones, the rate of photopolymerization increases with an increase in the volume of substituents in positions 3 and 6 of the quinoid ring of o-benzoquinone. It found that trialkylamines (dimethylethanolamine and dimethylcyclohexylamine) are more efficient as coinitiators of photopolymerization than N,N-dimethylaniline. For compositions based on 3,6-di-tert-butylbenzoquinone-1,2, the spectral-sensitivity range in the visible region is 400 to 650 nm with a maximum at 600 nm. This value coincides with the maximum of the absorption band of quinone, which corresponds to the S(n → π*) electronic transition of carbonyl groups.

Preparation and Characterization of UV-Curable Cyclohexanone-Formaldehyde Resin and Its Cured Film Properties

UV-curable cyclohexanone-formaldehyde (UVCF) resin was prepared with cyclohexanone-formaldehyde (CF) resin, isophorone diisocyanate (IPDI), and pentaerythritol triacrylate (PETA) as base substance, bridging agent, and functional monomer, respectively. The structure of UVCF was characterized by Fourier transform infrared spectroscopy (FT-IR),1H-nuclear magnetic resonance spectroscopy (1H-NMR), and gel permeation chromatography (GPC). The viscosity and photopolymerization behavior of the UV-curable formulations were studied. The thermal stability and mechanical properties of the cured films were also investigated. The results showed that UVCF resin was successfully prepared, the number of average molecular weight was about 2010, and its molecular weight distribution index was 2.8. With the increase of UVCF resin content, the viscosity of the UV-curable formulations increased. After exposure to UV irradiation for 230 s, the photopolymerization conversion of the UV-curable formulations was above 80%. Moreover, when the UVCF content was 60%, the formulations had high photopolymerization rate, and the cured UVCF films showed good thermal stability and mechanical properties.

Photopolymerizable phosphate acrylates as comonomers in dental adhesives with or without triclosan monomer units

Phosphate diacrylates (CO-DAP, TMP-DAP) based on castor oil or trimethylolpropane were synthesized and evaluated in dental adhesive formulations in comparison with 3-acryloyloxy-2-hydroxypropyl methacrylate phosphate (AMP-P). In an attempt to promote antibacterial activity, another photopolymerizable monomer (TCS-UMA) containing 5-chloro-2-(2,4-dichlorophenoxy)phenol moiety (triclosan) was prepared and incorporated in adhesive resins. Each of these monomers had a molecular structure confirmed by spectral methods. The photopolymerization rates for monomers (0.063–0.088s−1) were lower than those determined in the monomer combinations (0.116–0.158s−1) incorporating phosphate diacrylate (11wt.%), BisGMA (33wt.%), TEGDMA (10wt.%), UDMA (10wt.%) and HEMA (15wt.%), the degree of conversion varying between 63.4 and 74.5%. The formed copolymers showed high values for water sorption (18.65–57.02μg/mm3) and water solubility (3.51–13.38μg/mm3), and the contact angle was dependent on the presence of CO-DAP (θF1: 66.67°), TMP-DAP (θF2: 55.05°) or AMP-P (θF3: 52.90°) in the photocrosslinked specimens compared to the sample without phosphate monomer (θF4: 82.14°). The scanning electron microscopy image of the dentin–resin composite interface after applying our F1 formulation (pH: 4.1) and its light-curing for 20s supports the evidence of the formation of the hybrid layer with the tooth structure created by self-etching approach, with no gaps or cracks in the adhesive. A comparative analysis of the adhesion achieved with commercial adhesive systems (Single Bond Universal, C-Bond) rather indicates similarities than differences between them. The addition of triclosan methacrylate (1wt.%) into the formulation inhibited the bacterial growth of the Streptococcus mutans and Escherichia coli in the direct contact area due to the covalently linked antibacterial monomer.

Preparation of Asymmetric Porous Janus Particles Using Microfluidics and Directional UV Curing

Asymmetric porous Janus particles of poly(tripropylene glycol diacrylate) poly(TPGDA)) are prepared from TPGDA/4‐cyano‐4′‐pentylbiphenyl (5CB) mixtures using microfluidics and directional ultraviolet (UV) curing. Droplets of the TPGDA/5CB mixtures, which have been prepared successfully in the microfluidics channel, are photo‐polymerized in the off‐chip reservoir with a focused UV beam irradiated from beneath the reservoir. The isotropic TPGDA/5CB single phase is phase‐separated into two phases during the photopolymerization of TPGDA. The relative rate of photopolymerization compared with phase separation is different according to which hemisphere of the droplet is exposed to the UV beam. Rapid polymerization on the UV‐exposed hemisphere of the droplet produces small 5CB‐rich phase‐separated domains leading to a close and smooth structure, whereas slow polymerization on the opposite hemisphere produces large 5CB‐rich domains that induce an open and rough porous structure. These asymmetric porous Janus particles of poly(TPGDA) cause asymmetric swelling, in which the UV‐exposed hemisphere swell more than the other in the solvents due to the large porous surface area made by the small‐phase‐separated domain, which prevents the formation of a compact cross‐linked network structure. The complete dried droplet after the extraction of 5CB has an acorn‐like appearance, in which the swelled UV‐exposed hemisphere shrinks more than the other leading to a wrinkled structure. This new method combining microfluidics and directional UV curing provides a simple and unique way of fabricating asymmetric porous Janus particles and their functionalization with metal nanoparticles.

Synthesis and photopolymerization of novel, highly reactive phosphonated-urea-methacrylates for dental materials

An urea methacrylate (1) and two phosphonated methacrylates (2–3) were synthesized from 2-isocyanatoethyl methacrylate (IEM) and benzyl amine (1), diethyl aminomethylphosphonate (2) and diethyl amino(phenyl)methylphosphonate (3). Their photopolymerization rates are notably higher than commercial monomers, despite the presence of only one double bond. Their polymerization rates follow the order 1∼2>3∼triethylene glycol dimethacrylate (TEGDMA)>2-hydroxyethyl methacrylate (HEMA). A tendency toward high crosslinking density during thermal bulk polymerizations, low oxygen sensitivity and high conversions with benzophenone during photopolymerization indicated the importance of hydrogen abstraction/chain transfer reactions. It was found that the addition of the monomers to HEMA significantly increased its polymerization rate, proving their utility as replacements for TEGDMA as reactive diluents for 2,2-bis[4-(2-hydroxy-3-methacryloyloxy propyloxy) phenyl] propane (Bis-GMA). Copolymer systems containing 2 and 3 showed improved Tg values compared to Bis-GMA/TEGDMA systems.

Influence of Photopolymerization Characteristics on Thermo‐Mechanical Properties of Nanocomposites Utilizing Polymerizable Organoclays in Thiol‐Acrylate Systems

SummaryTo produce clay nanocomposites, photopolymerizable organoclays can react with monomers and incorporate into polymer matrices during the UV curing process. This research investigates the effects of polymerizable organoclays on the reaction behavior as well as the ultimate composite properties based on in‐situ thiol‐ene photopolymerization. To this end, different types of polymerizable organoclays, prepared by changing the functional group structure, were examined in various thiol‐acrylate systems. Small angle X‐ray diffraction was used to examine the degree of clay exfoliation. Photopolymerization behavior was characterized using real time infrared spectroscopy. Dynamic mechanical analysis was used for analyzing both mechanical and thermal properties. With sufficient clay exfoliation, the incorporation of thiol groups on the clay surfaces significantly increases the photopolymerization rate and final thiol conversion, whereas acrylate group conversion does not change significantly. While increasing monomer functionality does decrease final thiol conversion, the increase of thiol functionality of organoclays enhances thiol‐ene step growth reaction. Dark curing results suggest that the structure of propagating radicals on the clay surface varies by the type of polymerizable organoclays, changing the reaction behavior of the system. In accordance with the reaction behavior, the incorporation of acrylated organoclays significantly increases the storage modulus by inducing dominant acrylate homopolymerization. Addition of thiolated organoclays, on the other hand, makes more flexible polymer chains due to increased thio‐ether linkages.

Optimization of LC droplet size and electro‐optical properties of acrylate‐based polymer‐dispersed liquid crystal by controlling photocure rate

ABSTRACTWe investigated the effects of the different content ratios of 2‐ethylhexylacrylate (2‐EHA) and 2‐ethylhexylmethacrylate (2‐EHMA) on the relationships among the photopolymerization rate, morphology of liquid crystals (LCs) droplets, and electro‐optical properties of trifunctional urethane acrylate‐based polymer‐dispersed liquid crystal (PDLC) systems. Photo‐differential scanning calorimetry (DSC) analysis and resistivity measurement revealed that increasing 2‐EHMA content gradually decreased the photocure rate of trifunctional urethane acrylate‐based PDLCs, which prolonged the phase separation between the LC molecules and the prepolymers. Morphological observations and electro‐optical measurements demonstrated that trifunctional urethane acrylate‐based PDLCs with the 2‐EHA:2‐EHMA ratios from 4:1 to 3:2 in weight percent formed the favorable microstructures of LC droplets being within the range of 1–5 µm to scatter light efficiently and showed the satisfactory off‐state opacity and on‐state transmittance and the relatively low‐driving voltage. The microstructures of LC droplets and electro‐optical properties of trifunctional urethane acrylate‐based PDLCs could be usefully optimized by controlling the photocure rate using the different 2‐EHA/2‐EHMA content ratios. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3098–3104, 2013

Hybrid thiol–ene network nanocomposites based on multi(meth)acrylate POSS

First, multi(meth)acrylate functionalized POSS monomers were synthesized in this paper. Secondly, FTIR was used to evaluate the homopolymerization behaviors of multi(meth)acrylate POSS and their copolymerization behaviors in the thiol–ene reactions with octa(3-mercaptopropyl) POSS in the presence of photoinitiator. Results showed that the photopolymerization rate of multimethacrylate POSS was faster than that of multiacrylate POSS. The FTIR results also showed that the copolymerizations were dominant in the thiol–ene reactions with octa(3-mercaptopropyl) POSS, different from traditional (meth)acrylate-thiol system, in which homopolymerizations were predominant. Finally, the resulted hybrid networks based on POSS were characterized by XRD, FE-SEM, DSC, and TGA. The characterization results showed that hybrid networks based on POSS were homogeneous and exhibited high thermal stability.

Ketocoumarin/triazine/thiol as new high speed photoinitiating system for free radical polymerization under visible light in aerated media

This paper describes the development of a new photoinitiating system for free radical photopolymerization of a multifunctional acrylate monomer under visible light in aerated condition. A ketocoumarin dye is combined with a 1,3,5-triazine derivative as co-initiator, to produce initiating radical species that trigger the polymerization reaction. Aliphatic thiols are combined with the dye-triazine system to overcome the oxygen inhibition, and the effect of thiol concentration and functionality is examined. Photopolymerization kinetic data, as obtained from RT-FTIR spectroscopy experiments, show that the relative photopolymerization rates are not affected by the presence of oxygen. Indeed, the photoinitiation process remains highly efficient in aerated as well as in laminated conditions. The photochemical mechanisms involved in this three components system is investigated by laser flash photolysis.

Photosensitive acrylate copolymer for electrodeposition photoresist

A photosensitive random copolymer UPDHES was prepared by introducing the acrylate groups into the side chain of the copolymer composed of N,N-dimethylaminomethyl methacrylate (DMAEMA), 2-hydroxyethyl acrylate (HEA), 2-ethylhexyl acrylate (EHA), and styrene (St) (PDHES). The molecular structure of UPDHES was characterized by FTIR and 1H NMR analyses. Self-assembling of the random copolymer UPDHES in water formed positively charged photosensitive particles, and the particles were measured by TEM to be spherical-like nano-particles range from 20–90 nm. The oriented deposition of the particles on gold electrode was investigated with the cyclic voltammetry and TEM under low applied voltage. The influence of high applied voltage on current density in electrodeposition process and thickness of films were investigated also. Besides, the photopolymerization rate and final C=C conversion reached to the highest values with 3 wt % Irgacure 1173 addition, whereas decreased as further added. Moreover, an exposure-development procedure of electrodeposition UPDHES film produced developed diagram with resolution of 15 μm.

Synthesis and Photostructuring of Hybrid Photopolymers with Cinnamate and Anil Moieties by using UV Light and Femtosecond Laser Pulses

Two photosensitive methacrylates containing urea and two cinnamates (N,N–di(cinnamoyloxyethyl) N'-methacryloyloxyethyl urea, DC-MA), or urethane and saliciliden-aniline (anil) groups (methacryloyloxyethyl-2-carbamoyloxy(m-methyl, o-hydroxybenziliden)-aniline, UAn-MA) were synthesized and used besides N,N'-(methacryloxyethyldietoxy-methylsilylpropyl)-urea (UH-MA) in the preparation and photostructuring of hybrid photopolymers. Polymerization of the monomers was investigated by differential scanning photo calorimetry (photo-DSC), Fourier transform infrared (FTIR) and near-infrared (NIR) spectroscopies. The rate of photopolymerization increased upon adding UH-MA in formulation (DC-MA/UH-MA, Rp = 9.1 × 10−2 s−1; UAn-MA/UH-MA, Rp = 2.32 × 10−2 s−1), the degree of conversion being between 33 and 76%. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical microscopy confirmed the formation of bidimensional hybrid microstructures by using two-photon polymerization (2PP).

A computational approach to the free radical polymerization kinetics of alkyl α‐hydroxymethacrylate monomers: A structure–reactivity relationship

ABSTRACTDensity functional theory calculations at the B3LYP/6–31+G(d) level were carried out for 16 alkyl α‐hydroxymethacrylate (RHMA) monomers, and the calculated quantum chemical descriptors were used to construct a quantitative structure–activity relationship model of the reactivity parameters of those monomers. A multiple regression analysis was adopted to predict the polymerization kinetics. The molecular descriptors used in this study are the Mulliken and APT charges of the backbone C atoms in proximity of the reactive center, the total dipole moment (µ), the energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), the isotropic polarizability (α), the Mulliken atomic spin density (ρs), the ionization energy (IE), the electron affinity (EA), the resonance parameter (Res), the natural atomic orbital occupancies, and the bond distances of the bonds in the proximity to the reactive center of the RHMA monomers and their corresponding radicals. Among the various descriptors considered, the IE and EA of the monomers, the bond order of carbonyl double bond of monomer (BOCO), the resonance stabilization parameter of the monomeric radical, and the Mulliken atomic spin density (ρs) of C5 of the radical were found to be correlated (R2 = 0.9416) with the experimental rates of photopolymerization. The correlation with experiment is also satisfactory when additional monomers are included in the data set; a new correlation is thus generated (R2 = 0.9186). This study is expected to shed light on predicting the reactivities of RHMA monomers prior to their synthesis and to rank their photopolymerization rates based on their quantitative structural properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2375–2384

Preparation of a novel anti shrinking agent (SOC DA) and its evaluation in dental resins

AbstractIn this work is discussed the synthesis of a novel antishrinking agent (SOC DA) and the evaluation of its performance in an acrylic dental resin. SOC DA was photopolymerized in conjunction with the components of a conventional acrylic resin, which includes a mixture of diacrylate monomers [glycerolate bisphenol A dimethacrylate (BIS-GMA) / Urethane dimethacrylate (UDMA) / triethyleneglycol dimethacrylate (TEGDMA)] in 50/30/20 molar ratio). SOC DA was added in a range between 5.0-20.0 mol % with respect to the total amount of moles of the acrylic monomers. It was found that increasing concentrations of SOC DA, promoted higher conversions of the dimethacrylate monomers without decreasing the photopolymerization rate of the acrylate monomers. The study of the effect of SOC DA on the mechanical properties of the dental composite filled with 70 % of silicon dioxide, revealed that the presence of the antishrinking agent improved both the compressive and the flexural strength of the dental materials. Besides, it was found that by using the SOC DA at 20%, the shrinkage was reduced 52%, compared with the same formulation without SOC DA.

A benzophenone-bearing acid oligodimethacrylate and its application to the preparation of silver/gold nanoparticles/polymer nanocomposites

The synthesis of photosensitive urethane dimethacrylate that contains poly(ethylene oxide) sequence (PEG, Mw: 400), carboxylic and benzophenone moieties, and its characterization by specific methods (1H and 13C NMR, FTIR, UV and electrospray ionization-mass spectroscopy) are reported. UV curing parameters of this macromer (BP-UDMA) alone and in monomer combinations was evaluated through FTIR spectroscopy and photo-differential scanning calorimetry using 1 wt% 4-(dimethylamino)phenylacetic acid as co-initiator or Irgacure 819 (Irg819). The results show that the photopolymerization rates of the BP-UDMA are higher in the case of Irg819 (R max P : 0.108 s−1) due to its synergic action, whereas the degree of conversion of C=C double bond (DC, after 120 s of UV irradiation) is over 77 %. When other co-monomers (non-acid urethane dimethacrylate and silyl urea methacrylate) are incorporated into the formulation, the photopolymerization rate (0.095–0.132 s−1) and DC (84.59–79.69 %) varied in reasonable limits. Depending of the photoinitiator type, as well as the monomer composition, the addition of 0.5, 1 and 3 wt% noble metal precursors (AgNO3 and AuBr3) led to the formation of hybrid composites with in situ-synthesized nanoparticles (NPs), where the variations in the intensity of the surface plasmon absorption bands appeared in the range 400–456 nm (Silver) or 500–553 nm (Gold), better results being obtained in the first initiating system. Homogeneous dispersion of nanoparticles into the polymer matrix was evidenced by EDX and TEM analysis, the last proving the existence of nanoparticles with sizes around 10 nm and variable morphologies. X-ray diffraction analysis complemented these results.

Synthesis and cationic photopolymerization of phenyl epoxy-silicone monomers

Cationically photopolymerizable phenyl epoxy-silicone monomers (Ep-Ph-Si) with a high RI and high photopolymerization activity have been synthesized via sequential hydrosilylation reactions of 1,3,5,7- tetramethylcyclotetrasiloxane by attaching first styrene, followed by 4-vinyl-1-cyclohexene-1,2-epoxide in the presence of Lamoreaux catalyst. The content of benzene ring in the monomers was determined by 1HNMR; the epoxy value was examed by chemical titration. The RI of the obtained monomers showed that the benzene ring could improve the refractive indices (RIs) and the RIs of the phenyl epoxy-silicone monomers ranged from 1.50 to 1.52. The cationic photopolymerization of these monomers initiated by triarylsulfonium hexafluorophosphate (P-S) showed that phenyl epoxy-silicone monomers with little amount of benzene ring still exhibited high photopolymerization rate. Those properties are well suitable for the application in UV-curing optical coatings and encapsulation materials.

Photoinitiated polymerization of acrylate, methacrylate, and vinyl ether end‐functional polyisobutylene macromonomers

AbstractPolyisobutylene‐based UV cured networks potentially useful as sealants were synthesized by photopolymerization of well‐defined polyisobutylene methacrylate (PIB‐MA), acrylate (PIB‐A) and vinyl ether (PIB‐VE) di‐ and trifunctional macromonomers. The kinetics of photocrosslinking were measured using an optical pyrometer apparatus and optimized with respect to different experimental parameters. PIB‐MA/A macromonomers displayed enhanced reactivity in radical photopolymerization in the presence of a bis(acylphosphine) oxide photoinitator. PIB‐VE macromonomers exhibited a high rates of photopolymerization with (4‐n‐octyloxyphenyl)phenyliodonium hexafluroantimonate as the photoinitiator. The rates as well as the ultimate monomer conversions were increased by increasing the irradiation light intensity. The inherent induction period associated with oxygen inhibition in the photopolymerization of PIB‐MA was significantly reduced by optimizing the choice of photoinitiator. A detailed investigation of the concentration of MA/A/VE end groups revealed the presence of a prominent saturation effect in the photopolymerization of PIB‐A, which was absent with PIB‐MA and PIB‐VE. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Synthesis and polymerization kinetics of acrylamide phosphonic acids and esters as new dentine adhesives

AbstractIn restorative dentistry, acrylamide monomers bearing phosphonic acid moieties have proved to be useful species for the formulation of dental self‐etch adhesives since they provide enhanced adhesion to hydroxyapatite and are not subject to hydrolysis, thus potentially improving their adhesive durability. Previous studies have demonstrated that phosphonic acid acrylamides increase the rate of photopolymerization of diacrylamide monomers. To understand whether this rate acceleration is specific to the acrylamide function of the monomer, or due to the phosphonic acid group per se, or is applicable only with a crosslinking reaction, we have synthesized several acrylamide and methacrylate monomers bearing phosphonic acid or phosphonate moieties and studied their photopolymerization kinetics. The acrylamide phosphonic acid was found to accelerate the polymerization rate but similar monomers bearing a phosphonate ester group had a much smaller effect. A similar accelerating effect was observed when the phosphonic acid‐based monomers were copolymerized with a monofunctional acrylamide monomer, excluding the possibility that the rate acceleration might be related to the crosslinking process. This rate effect is also observed when a nonpolymerizable organic phosphonic acid is present in the polymerizing medium. We suggest that the increase of the medium polarity is responsible for this rate enhancement effect. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

One-pot synthesis of photocrosslinked sol–gel hybrid composites containing silver nanoparticles in urethane-acrylic matrixes

The synthesis of new urethane dimethacrylate oligomers based on polytetrahydrofuran (PTHF)/poly(butylene adipate) (PBA): trimethyl-1,6-diisocyanatohexane (TMDI): 2-hydroxyethyl methacrylate (HEMA) (molar ratio 1:2:2) is presented. Organic–inorganic hybrid composites comprising urethane methacrylic macromers and 3-(trimethoxysilyl)propyl methacrylate (MPTS) taken in various gravimetric ratios were prepared by one-pot process through the UV-curing of photopolymerizable mixtures in the presence of 1wt.% Irgacure 819 photoinitiator, followed by the sol–gel reactions (hydrolysis and condensation) at ambient temperature. Additionally, in some formulations prior obtained silver nanoparticles (AgNPs) were incorporated before photopolymerization. Infrared spectroscopy monitored the microstructural evolution of the silica phase as well as the progress of double bond conversion during photopolymerization, while photo-differential scanning calorimetry (photo-DSC) gave us information on polymerization rate and conversion. The photopolymerization results show that the photopolymerization rates of the hybrid formulations are in the range of 0.084–0.158s−1, whereas the conversion degree after 5min of UV irradiation is over 70%. The thermal stability, Young’s modulus and tensile strength of the hybrid films are enhanced with the increase in alkoxysilane content, indicating significant reinforcement of the matrix in the presence of SiOSi linkages. The existence and homogeneous dispersion of nanosilver into the polymer matrix has been supported by EDX and TEM analysis, the last allowing a visualization of the formation of silver nanoparticles with size between 2 and 13nm (mean diameter 6.3nm). The four diffraction peaks appeared in the wide angle X-ray scattering spectrum can be assigned to the face-centered cubic silver phase, indicating the formation of metallic silver. The water/ethanol resistance for the hybrid coatings is augmented by the increase of inorganic content.

Fabrication of Nanoengineered Metallic Structures and Their Application to Nonlinear Photochemical Reactions

Abstract We used metallic nanoparticles exhibiting localized surface plasmon resonance and electromagnetic (EM) field enhancement effects induced by plasmon excitation for the photochemical reaction field; this approach makes it possible to increase the probability of an interaction between photons and the materials. EM field enhancement effects induced by gold nanostructures were elucidated using two-photon-induced photoluminescence from nanogap-spaced gold nanoparticles. The photoluminescence was promoted mainly in the surface regions of the gold nanoblocks adjacent to the nanogaps due to the EM field enhancement effect. To elucidate the near-field intensity distribution of the nanogap gold structures, we investigated the photopolymerization of a commercially available negative photoresist assisted by EM field enhancement in the nanogaps separating the gold nanoblocks. Photopolymerization rates were enhanced by several orders of magnitude in the gold nanoblock structures that contained nanogaps narrower than 10 nm. We propose two surface plasmon-assisted nanolithography techniques based on spatially selective photochemical reactions promoted by the EM field enhancement effect. The first method uses ultimate near-field lithography with a local near-field distribution induced in the nanogaps, and the second technique uses the scattering component of multipole plasmon resonance as an exposure mechanism. These lithographic techniques represent a type of application based on plasmon-enhanced chemical reactions.