Photopolymerization Of Monomers Research Articles

Evaluation of new coinitiators of camphorquinone useful in the radical photopolymerization of dental monomers

This work reports the design and synthesis of two new monomers with tertiary amines and four methacrylic (MBTTM) or acrylic (MBTTA) terminal unsaturations, and their evaluation as coinitiators in the photopolymerization of monomers useful in dentistry. Both monomers were characterized by FT-IR, 1H NMR, and UV–vis spectroscopies. Experimental Bis-GMA/TEGDMA or UDMA/TEGDMA resins were formulated using camphorquinone as the photoinitiator and the MBTTM or MBTTA compounds as coinitiators. As control, resins using EDAB as coinitiator were formulated. The photopolymerizable resins formulated using the new coinitiators achieved double bond conversion values close to 40% in 30 s. Regarding polymerization rate, experimental resins formulated with MBTTM or MBTTA had lower values. The flexural strength of the experimental BisGMA/TEGDMA resins did not have statistically significant differences with the control group (p > 0.05). On the other hand, the experimental resins formulated with UDMA/TEGDMA presented higher flexural strength and elastic modulus. Finally, the cell viability test showed that none of the resins formulated with MBTTM or MBTTA as coinitiators were cytotoxic. Due to their characteristics, MBTTM and MBTTA monomers are potentially useful as coinitiators in the formulation of photopolymerizable materials for dental use.

NIR Light-Induced ATRP for Synthesis of Block Copolymers Comprising UV-Absorbing Moieties.

NIR exposure at 790 nm activated photopolymerization of monomers comprising UV‐absorbing moieties by using [CuII/(TPMA)]Br2 (TPMA=tris(2‐pyridylmethyl)amine) in the ppm range and an alkyl bromide as initiator. Some of them comprised structural elements selected either from those showing proton transfer or photocycloaddition upon UV excitation. Polymers obtained comprise living end groups serving as macroinitiator for controlled synthesis of block copolymers with relatively narrow molecular weight distributions. Chromatographic results indicated formation of block copolymers produced by this synthetic approach. Free‐radical polymerization of monomers pursued for comparison exhibited the expected broader dispersity of molecular weight compared to photo‐ATRP. Polymerization of these monomers by UV photo‐ATRP failed on the contrary to NIR photo‐ATRP demonstrating the UV‐filter function of the monomers. This work conclusively provides a new approach for the polymerization of monomers comprising UV‐absorbing moieties through photo‐ATRP in the NIR region. This occurred in a simple and efficient pathway. However, studies also showed that not all monomers chosen successfully proceeded in the NIR photo‐ATRP protocol.

UV-Nanoimprinting Lithography Photoresists with No Photoinitiator and Low Polymerization Shrinkage

In this work, a photopolymerizable disulfide monomer containing C(acryl)-S, disulfanediyl bis(4,1-phenylene) diacrylate (ADSDA), was designed and synthesized. Then, the UV nanoimprinting lithograph...

A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers

AbstractSmart windows are very attractive because they not only provide comfortable indoor conditions for cars and buildings, but also protect privacy. However, current smart windows have problems such as high energy consumption, slow response time, and poor stability. To solve these problems, a single‐step dual stabilization (SSDS) is newly proposed for the fabrication of robust liquid crystal (LC) smart windows switching fast at low voltage. Upon irradiating ultraviolet light on the selected area of the nematic (N) LC optical cell with photoisomerizable macrogelators (B3AZ) and photopolymerizable monomers, NLC physical gels (LCPGs) and partition walls are simultaneously constructed. LCPGs play a role of light shutter under a low electric field (9.6 Vpp) which is ten times lower than that of the conventional polymer‐stabilized LC‐based smart windows. Partition walls constructed by the selected area photopolymerization significantly enhance the mechanical stabilities. Based on the experimental results, it is realized that the NLC layer generated near the partition walls makes the LCPGs respond to a low voltage. Robust SSDS smart windows could open new doors for the development of high‐performance smart windows.

Photoclick chemistry to create dextran-based nucleic acid microarrays.

In the literature, there are reports of the utilization of various hydrogels to create generic platforms for protein microarray applications. Here, a novel strategy was developed to obtain high-performance microarrays. In it, a dextran hydrogel is used to covalently immobilize oligonucleotides and proteins. This method employs aqueous solutions of dextran methacrylate (Dx-MA), which is a biocompatible photopolymerizable monomer. Capture probes are immobilized inside the hydrogel via a light-induced thiol-acrylate coupling reaction at the same time as the dextran polymer is formed. Hydrogel microarrays based on this technique were prepared on different surfaces, such as a Blu-ray Disk and polycarbonate or alkene-functionalized glass slides, and these systems showed high probe-loading capabilities and good biorecognition yields. This methodology presents advantages such as a low cost, a short analysis time, a low limit of detection, and multiplexing capabilities, among others. Confocal fluorescence microscopy analysis demonstrated that in these hydrogel-based microarrays, receptor immobilization and the biorecognition event occurred within the hydrogel and not merely on the surface.

A two-step exposure method with interleaved phase pages for recording of SQAM signal in holographic memory

We have proposed a two-step exposure method (TEM) for recording spatial quadrature amplitude modulated (SQAM) signals in holographic memories. We consider two generation methods of the phase pages used in the TEM and investigate the reproduction accuracy of the SQAM signal. One of them is to produce the phase pages by arranging from the conventional two-phase pages alternately. We indicate that it is able to reduce the consumption of photopolymerizable monomers in the photopolymer effectively by using the phase distribution. It also suppresses the adverse effect on the reproduction accuracy of SQAM signal by intensity variation of the multiplexed holograms. Further, we propose the method to produce the SQAM signals by a one-shot recording based on the analysis.

Microstructured Photopolymerization of Liquid Crystalline Elastomers in Oxygen‐Rich Environments

AbstractLiquid crystal elastomers (LCEs) are soft materials that undergo large anisotropic shape change in response to stimuli. Rational organization of the local director field can impart spatial control of the strain profile, enabling stretch‐based deformation capable of nearly 20 J kg−1 of output force. LCEs are increasingly being considered in end‐use applications in robotics, therapeutics, and optics. Here, a new synthetic approach is introduced to prepare LCEs composed of main chain mesogens via the cationic photopolymerization of the epoxy liquid crystal monomer (LCM). This examination details the optical, mechanical, and thermal properties of epoxide‐based LCEs as a function of spacer length (3, 6, or 11 carbons). The oxygen insensitivity of the cationic photopolymerization of these monomers makes this approach particularly attractive for implementation with emerging additive manufacturing techniques. This contribution focuses on microstructuring LCEs via 2‐photon direct laser writing (2P‐DLW). A custom heated cell facilitated 2P‐DLW of the aligned LCE epoxy resin melts to fabricate diverse geometric arrays. Enabled by the orthogonality of the reaction chemistry, hybrid and microstructured material compositions are prepared via the encapsulation of LCE epoxy micropatterns with free‐radical polymerization of acrylate‐based LCEs. The distinct thermomechanical response of the hybridized and microstructured LCE composites enables local and spatially controlled actuation.

Analysis of Double Bond Conversion of Photopolymerizable Monomers by FTIR-ATR Spectroscopy

An experiment for the calculation of the degree of double bond conversion, after a polymerization reaction, of photopolymerizable liquid monomers using FTIR-ATR spectroscopy is reported. The experi...

TiO2‐Based Photopolymerized Hybrid Catalysts with Visible Light Catalytic Activity Induced by In Situ Generated Ag/Au NPs

AbstractThis work describes the use of surface modified TiO2 nanoparticles in combination with photopolymerizable monomers in the achieving of hybrid photocrosslinked polymer networks for photocatalysis. The surface of TiO2 nanoparticles was functionalized by means of a silane coupling agent with acrylic sequences and quaternary ammonium units in order to attain a covalent linkage of the nanoparticles inside the photocured matrix. To increase the photocatalytic performance of TiO2 NPs and to expand its catalytic activity under visible light, Ag/Au NPs were in situ photogenerated in the acrylic matrix simultaneously with the photopolymerization process. The photopolymerization profile, diffraction patterns and nanoparticles distribution were established for the hybrid films by FTIR, XRD and TEM, respectively. Additionally, the hybrid films exhibited good antibacterial properties against Staphylococcus aureus and Escherichia coli. The photocatalytic efficiency of the hybrid coatings was tested on phenol and Congo Red photodecomposition under UV and visible light irradiation, the best results being observed for the materials incorporating Ag/Au NPs.

Polymerization of cubosome and hexosome templates to produce complex microparticle shapes

Cubic and hexagonal liquid crystalline particles, or cubosomes and hexosomes, are used as templates to polymerize various monomers to produce particles with unique micron-scale geometric shapes. Emulsion droplets containing water, ethanol, and the lipid glyceryl monooleate are suspended in a yield stress fluid and used to produce shapes based on cubic and hexagonal symmetry by slow crystallization. The underlying liquid crystalline ordering of the aqueous lipid system drives symmetric shape formation, while its amphiphilicity allows incorporation of various organic monomers. Photopolymerization of monomers in the lipid templates creates polymeric particles shaped like polyhedra based on cubic symmetry as well as biconical cylinders based on hexagonal symmetry, and their shape is preserved after template removal. Product particle shapes are controlled by varying the structures and hydrophobicity of the monomers, as they control formation of different phases and microstructures. Monomer polarity determines whether the template can exhibit hexagonal phase, as when divinylbenzene is used, or cubic phase, when di(ethylene glycol) dimethacrylate is used. The monomers also control the microstructure of the final particles produced, forming rigid shapes composed of linked polymer nanospheres when divinylbenzene or di(ethylene glycol) dimethacrylate are used, and soft hydrogel particles when N,N'-methylenebisacrylamide is used.

3D Printing Enabled Customization of Functional Microgels.

Injectable microgels show great promising applications in cell therapy and drug delivery. Currently, there remains a challenge to rapidly and cost-effectively fabricate customized microgels. Here, we present a digital light processing based three-dimensional (3D) printing process to fabricate microgels with tailored shapes and sizes. The microgels are constructed by the digital light controlled polymerization of photopolymerizable monomer solution within 2 s. By mixing nanoparticle-encapsulated drugs into the monomer solution, the microgels with sustained drug release can be readily prepared. Also, cells can be printed into microgels with survival and proliferation. In conclusion, this study provides a 3D printing process for customizing functional microgels containing drugs or cells with potential therapeutic applications.

Confinement of an antiferroelectric liquid crystal in a polymer nanonetwork: thermal and dielectric behaviour

We report the thermal and dielectric investigations on a liquid crystal exhibiting an antiferroelectric phase and confined in a polymer network of sub-micron dimensions. Two different photo-polymerizable monomers have been employed for the purpose: one of them (HDDA) is bereft of any aromatic parts, while the other (RM82) contains aromatic as well as aliphatic units and, in fact, forms a liquid crystalline phase in its monomeric state. The polymerization, which is carried out in the presence of the liquid crystalline host, is expected to yield a nanosegregated structure for HDDA and blended structure for the RM82 case, the difference reflecting the morphologies of the networks, as evidenced by SEM images. Surprisingly, even a small concentration of the latter polymer added to the former variety has substantial influence on the morphology. The main work focusses on calorimetry and dielectric relaxation spectroscopy of the host liquid crystal confined in these nanonetworks created by the polymers, which can be considered to form virtual surfaces with a finite anchoring energy. We have investigated the in-phase and antiphase modes in the antiferroelectric phase, and the soft mode in the paraelectric phase preceding the antiferroelectric phase. The relaxation frequencies of all these modes are substantially influenced by the network, with the results showing certain surprises in cases containing both HDDA and RM82.

Fabrication of Dense Silica Ceramics through a Stereo Lithography-Based Additive Manufacturing

Silica ceramics were fabricated via an additive manufacturing process based on stereolithography. Ceramic suspension with low viscosity and high solid loading is of importance to stereolithography based UV-curable. In this work, to meet the requirements of stereolithography, effects of temperature, additive content and ball-milling time on the viscosity of silica slurry were investigated, and properties of silica ceramics sintered at different temperature were also researched.The results show that increasing temperatures strongly decrease the viscosity unless when the temperature is above 70°C. The minimum of viscosity was observed for an appropriate addition of dispersant, which is corresponding to the best dispersion state of silica particles in the photopolymerizable monomer. And optimizing ball-milling time showed the lowest viscosity suitable for the stereolithography process. The appropriate temperature, additive content and ball-milling time facilitating stereolithography was 70°C, 2% and 60min respectively. The prepared ceramics sintered at 1220°C showed a density and flexural strength of 1.57g/cm3 and 13.31MPa respectively.

39.4: Invited Paper: Self‐alignment of liquid crystal for multi‐domain liquid‐crystal display

By introducing photopolymerizable amphiphile organic monomers(PAOM) into nematic liquid crystals (NLC) with controlled amount of UV‐curable reactive mesogen (RM), a amulti‐domain vertical‐alignment LC device was successfully demonstrated. The device, possessing a vertically aligned LC director in four different azimuthal directions, exhibited a fast response time,wide‐viewing‐angle characteristics and high voltage holding ratio(VHR), in the absence of conventional polyimides vertical‐alignment layers. The formation of automatic and robust vertical alignment layer was anlayzed by using scanning electron microscopy(SEM).

Microfluidic Production of Capsules‐in‐Capsules for Programed Release of Multiple Ingredients

AbstractCapsules with thin shells have a high‐loading capacity and are thus well‐suited containers for reagents that must be stored in confined volumes. Capsules contained in larger capsules, so‐called double capsules, allow the encapsulation of distinct reagents within small, defined, well‐separated volumes. Therefore, they offer possibilities to initiate reactions in confined volumes and to release distinct bioactives sequentially while minimizing the risk for cross contaminations. In this study, a new microfluidic capillary device is presented that enables the assembly of water‐oil‐water‐oil‐water (W/O/W/O/W) quadruple‐emulsion drops whose oil layers are ultra thin. These quadruple emulsions can be converted into double capsules with thin membranes through either evaporation‐induced consolidation of biodegradable polymers or photopolymerization of monomers. It is demonstrated that the membrane composition of the inner and outer capsules can be independently selected to enable programed release of distinct encapsulants. For example, biodegradable polymers with two different degradation rates are employed as the membrane materials that enable sequential release of two different encapsulants. In addition, the release of the encapsulants can be triggered by external stimuli such as osmotic pressure. This new class of double capsules provides new opportunities for drug delivery and screening assays that require sequential release of multiple water‐soluble ingredients.

Photopolymerizable multifunctional monomers and their evaluation as reactive Bis‐GMA eluents

ABSTRACTBis‐GMA {2,2‐bis[4‐(2′‐hydroxy‐3′‐methacryloyloxy‐propoxy)‐phenyl]‐propane}, TEGDMA <2‐{2‐[2‐(2‐methylprop‐2‐enoyloxy)ethoxy]ethoxy}ethyl‐2‐methylprop‐2‐enoate>, and methyl methacrylate (MMA) are some of the most commonly used monomers in the field of restorative dentistry. These compounds are characterized by having one or two terminal double bonds. Besides the effort to synthesize new monomers, several problems still affect the clinical behavior of contemporary dental materials. In this work, two monomers with three terminal double bonds, 5A13DA and 5A13DMA, were synthesized. Both monomers were used to completely replace TEGDMA as reactive diluent of photopolymerizable dental resin composites containing Bis‐GMA. The effects of 5A13DA and 5A13DMA on flexural properties, double bond conversion, water sorption, solubility, and polymerization shrinkage were evaluated. In addition, both monomers were evaluated as crosslinking agents for methylmethacrylate, resulting in copolymers with enhanced thermal stability. The results obtained suggest that newly synthesized monomers are potential substitutes for TEGDMA in the formulation of dental composites, providing 50% lower volumetric shrinkage than the composite resin used as control and adequate mechanical properties. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46240.

Anisotropic piezoresistivity characteristics of aligned carbon nanotube-polymer nanocomposites

Dielectrophoresis under the application of AC electric fields is one of the primary fabrication techniques for obtaining aligned carbon nanotube (CNT)-polymer nanocomposites, and is used here to generate long range alignment of CNTs at the structural level. The degree of alignment of CNTs within this long range architecture is observed via polarized Raman spectroscopy so that its influence on the electrical conductivity and piezoresistive response in both the alignment and transverse to alignment directions can be assessed. Nanocomposite samples consisting of randomly oriented, well dispersed single-wall carbon nanotubes (SWCNTs) and of long range electric field aligned SWCNTs in a photopolymerizable monomer blend (urethane dimethacrylate and 1,6-hexanediol dimethacrylate) are quantitatively and qualitatively evaluated. Piezoresistive sensitivities in form of gauge factors were measured for randomly oriented, well dispersed specimens with 0.03, 0.1 and 0.5 wt% SWCNTs and compared with gauge factors in both the axial and transverse to SWCNT alignment directions for electric field aligned 0.03 wt% specimens under both quasi-static monotonic and cyclic tensile loading. Gauge factors in the axial direction were observed to be on the order of 2, while gauge factors in the transverse direction demonstrated a 5 fold increase with values on the order of 10 for aligned specimens. Based on Raman analysis, it is believed the higher sensitivity of the transverse direction is related to architectural evolution of misaligned bridging structures which connect alignment structures under load due to Poisson’s contraction.

Cellulose Nanocrystal Inks for 3D Printing of Textured Cellular Architectures

3D printing of renewable building blocks like cellulose nanocrystals offers an attractive pathway for fabricating sustainable structures. Here, viscoelastic inks composed of anisotropic cellulose nanocrystals (CNC) that enable patterning of 3D objects by direct ink writing are designed and formulated. These concentrated inks are composed of CNC particles suspended in either water or a photopolymerizable monomer solution. The shear‐induced alignment of these anisotropic building blocks during printing is quantified by atomic force microscopy, polarized light microscopy, and 2D wide‐angle X‐ray scattering measurements. Akin to the microreinforcing effect in plant cell walls, the alignment of CNC particles during direct writing yields textured composites with enhanced stiffness along the printing direction. The observations serve as an important step forward toward the development of sustainable materials for 3D printing of cellular architectures with tailored mechanical properties.

Effect of a Polymercaptan Material on the Electro-Optical Properties of Polymer-Dispersed Liquid Crystal Films.

Polymer-dispersed liquid crystal (PDLC) films were prepared by the ultraviolet-light-induced polymerization of photopolymerizable monomers in nematic liquid crystal/chiral dopant/thiol-acrylate reaction monomer composites. The effects of the chiral dopant and crosslinking agents on the electro-optical properties of the PDLC films were systematically investigate. While added the chiral dopant S811 into the PDLC films, the initial off-state transmittance of the films was decreased. It was found that the weight ratio among acrylate monomers, thiol monomer PETMP and the polymercaptan Capcure 3-800 showed great influence on the properties of the fabricated PDLC films because of the existence of competition between thiol-acrylate reaction and acrylate monomer polymerization reaction. While adding polymercaptans curing agent Capcure 3-800 with appropriate concentration into the PDLC system, lower driven voltage and higher contrast ratio were achieved. This made the polymer network and electro-optical properties of the PDLC films easily tunable by the introduction of the thiol monomers.

Structure and optical properties of the silver/polyacrylonitrile nanocomposites

Small-angle X-ray scattering is used to prove the formation of silver nanoparticles with sizes of 5–11 nm in siver/polyacrylonitrile nanocomposites synthesized via photopolymerization of a mixture containing silver, acrylonitrile, and photoinitiator. Optical spectra of nanocomposites obtained under different conditions are studied. The absorption spectra exhibit maxima at wavelengths of 420–450 nm related to the surface plasmon resonance of silver nanoparticles. IR spectra of the nanocomposites prove the formation of polyacrylonitrile in the course of the photopolymerization of monomer. The formation of metal nanoimpurities in polymer matrix leads to an increase in the intensity of photoluminescence and Raman scattering of polyacrylonitrile.