Multifunctional Acrylate Monomers Research Articles

Additively Manufactured 3D Micro-bioelectrodes for Enhanced Bioelectrocatalytic Operation

The drive toward miniaturization of enzyme-based bioelectronics established a need for three-dimensional (3D) microstructured electrodes, which are difficult to implement using conventional manufacturing processes. Additive manufacturing coupled with electroless metal plating enables the production of 3D conductive microarchitectures with high surface area for potential applications in such devices. However, interfacial delamination between the metal layer and the polymer structure is a major reliability concern, which leads to device performance degradation and eventually device failure. This work demonstrates a method to produce a highly conductive and robust metal layer on a 3D printed polymer microstructure with strong adhesion by introducing an interfacial adhesion layer. Prior to 3D printing, multifunctional acrylate monomers with alkoxysilane (-Si-(OCH3)3) were synthesized via the thiol-Michael addition reaction between pentaerythritol tetraacrylate (PETA) and 3-mercaptopropyltrimethoxysilane (MPTMS) with a 1:1 stoichiometric ratio. Alkoxysilane functionality remains intact during photopolymerization in a projection micro-stereolithography (PμSLA) system and is utilized for the sol-gel reaction with MPTMS during postfunctionalization of the 3D printed microstructure to build an interfacial adhesion layer. This leads to the implementation of abundant thiol functional groups on the surface of the 3D printed microstructure, which can act as a strong binding site for gold during electroless plating to improve interfacial adhesion. The 3D conductive microelectrode prepared by this technique exhibited excellent conductivity of 2.2 × 107 S/m (53% of bulk gold) with strong adhesion between a gold layer and a polymer structure even after harsh sonication and an adhesion tape test. As a proof-of-concept, we examined the 3D gold diamond lattice microelectrode modified with glucose oxidase as a bioanode for a single enzymatic biofuel cell. The lattice-structured enzymatic electrode with high catalytic surface area was able to generate a current density of 2.5 μA/cm2 at 0.35 V, which is an about 10 times increase in current output compared to a cube-shaped microelectrode.

Free-radical photoring-opening polymerization of cyclic allylic sulfide: From photocleavable photoinitiators to three components photoredox systems

Photopolymers form a family of materials that have been developed to meet specific demands in fields such as coatings, varnishes, semiconductors, optical fibers, printing plates, holographic recording, etc. However, the multifunctional acrylate monomers currently used present an important volume contraction. A drawback for applications where little shrinkage during polymerization is mandatory to keep shapes and properties of the material. To overcome this problem, monomers reacting by ring opening polymerization can be used. Among possible monomers, cyclic allylic sulfides are very interesting candidates: they are highly reactive and their polymerization mechanism is almost not affected by the presence of oxygen. In this work the effects of the photoinitiating systems on the free radical ring opening photopolymerization kinetics of an eight-member cyclic allylic sulfide is studied. It is shown that cleavable type I, bimolecular type II and three components redox photoinitiating systems allow the formation of linear photopolymers with high polymerization rates and final conversions. The photopolymerization kinetics obtained show that the photopolymerization is not sensitive to oxygen which leads to reduced exposure time and higher sensitivity. This remarkable property should also extend the usage of such monomers in the coating applications where oxygen inhibition is a drawback. Finally, the benefit of ring opening polymerization process is demonstrated trough the volume contraction measurement which was found to be lower than 1.5%.

Photoinitiation abilities of indeno- and indoloquinoxaline derivatives and mechanical properties of dental fillings based on multifunctional acrylic monomers and glass ionomer

Photopolymerization is a rapidly expanding technology with a wide variety of applications, from imaging to biomedical uses. Here, we present enhanced photosensitization of polymerization by photoredox pairs based on indene- and indoloquinoxaline dyes and thiophenoxyacetic acid for dental applications. The photoinitiating ability of the two-component systems was tested using several multifunctional monomers of various structures typical for dental fillings. The new photoinitiating systems show excellent efficiency in initiating free radical polymerization which occurs by photoinduced intermolecular electron transfer (PET) mechanism. Modification of the dye structure by extending the chain of conjugated π bonds, the arrangement of aromatic rings and the type of heteroatom, allowed to change the spectroscopic properties of the tested compounds and use them as absorbers of light emitted by dental lamps. The improved mechanical properties of the cured polymers, i.e., lowering the temperature during photopolymerization and an increase in polymer hardness were observed for the proposed photoinitiating systems compared to the camphorquinone – photoinitiator traditionally used in dentistry. This indicates that the dye – thiophenoxyacetic acid systems may be useful as photoinitiators in dental applications. The undoubted advantage of these photoinitiating systems is the elimination of the toxic aromatic amines traditionally used as co-initiators from the dental composition. It was possible thanks to the use of thiophenoxyacetic acid. Its application does not reduce the polymerization rate and does not extend the photocuring time.

Influence of Block Copolymer Concentration and Resin Crosslink Density on the Properties of UV‐Curable Methacrylate Resin Systems

AbstractAdditive manufacturing is on the verge of replacing established processes in dentistry, as it offers the possibility of manufacturing individual parts simply and cost‐effectively. Due to its suitability for a wide variety of materials and, above all, its high precision, the focus is currently on stereolithographic processes. Intrinsic brittleness of the used multifunctional acrylic monomers remains however one of the major challenges. One promising concept is the use of block copolymers (BCPs) guaranteeing minor effects on 3D‐printing processing and UV‐curing due to initially at least partial solubility, and hence low viscosity impact. A polycaprolactone‐polysiloxane (PCL‐PDMS‐PCL) triblock copolymer is synthesized via ring‐opening polymerization of caprolactone and used in radical UV‐cured methacrylic resin systems. Small angle X‐ray scattering measurements reveal the self‐assembly of the BCPs to objects of around 20 nm prior to curing. Subsequently, thermo‐mechanical characterization is carried out by dynamic mechanical analysis, flexural testing, and fracture toughness measurements (KIC). Transmission electron microscopy and scanning electron microscopy micrographs show a homogenous distribution of the BCPs and effective toughening via cavitation and shear yielding. The influence of the crosslink density on the toughness and the high effectiveness of block copolymers for improving fracture toughness is clearly shown.

Interparticle photo-cross-linkable Pickering emulsions for rapid manufacturing of complex-structured porous ceramic materials

A new series of Pickering emulsions that can be photo-cured by interparticle photo-cross-linking reactions using small amounts of multifunctional acrylate (MA) monomers is proposed to rapidly manufacture complex-structured porous ceramic materials. In our new process, water in oil (w/o) Pickering emulsion was designed by vigorous mixing of water and polyethyleneimine partially complexed with oleic acid (PEI–OA)-stabilized SiO2/toluene suspension containing small amounts of MA and a photo-radical initiator. Ultraviolet light irradiation to this w/o Pickering emulsion induced the formation of interparticle photo-crosslinks, which resulted in successful photocuring by photo-radical polymerization of MA and the Michael addition reaction between the polymerized MA and PEI–OA on the particles in the oil phase. We further applied the newly designed photo-curable Pickering emulsion and demonstrated that SiO2 components with pores related to the dispersed aqueous phase and complexed outer structures could be shaped via silicone molding or a hybridized approach of photocuring and green machining. Because of the reduced amounts of MA used, the porous SiO2 green components could be heat-treated using rapid heating profiles without any structural collapse for dewaxing and partial sintering.

Highly photosensitive furan acrylate derivatives and their solid-state photopolymerization

Highly photosensitive multifunctional furan acrylate monomers synthesized from biomass furfural can be photopolymerized into polyesters without photoinitiators and solvents.

Fully cross-linked UV-induced peelable acrylic PSA prepared from a dual curable castor oil based urethane acrylate oligomer for wafer dicing

For UV-induced peelable pressure sensitive adhesive (PSA) used in the wafer dicing process, improving the peel performance can effectively increase the process reliability and the yield of subsequent packaging process. In this work, a NCO-containing castor oil-based urethane acrylate oligomer called CO-PUB with dual curable functions (UV-induced polymerization and NCO/OH reaction) was obtained by partially sealing a castor oil-based urethane oligomer with hydroxyethyl acrylate. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectrometer (NMR) results indicated that CO-PUB was successfully prepared. CO-PUB, OH-containing acrylic copolymer, multifunctional acrylate monomer and photo-initiator were used to construct a UV-induced peelable adhesive for silicon wafer dicing. The results showed that NCO groups in CO-PUB underwent the NCO/OH reaction with the acrylic copolymer to obtain a vinyl pendant cross-linked acrylic copolymer. The peel strength of this peelable adhesive before UV irradiation could exceed 20 N/25 mm. After UV irradiation, the unsaturated vinyl bonds contained in it were copolymerized with the multifunctional acrylate monomer to form a fully cross-linked adhesive film and the peel strength could be reduced to below 1 N/25 mm. Compared with UV-induced peelable adhesives prepared by other reported curing agents, the adhesive prepared from CO-PUB reduced UV dose required for curing. The cross-linking degree of cured adhesive film was also increased and the gel content was up to 95%. The residual adhesive after peeling off could be reduced to about 0.32%. In addition, CO-PUB used renewable castor oil as polyol and did not need to add any organic solvent during the preparation process, providing a new idea for the green preparation of UV-induced peelable adhesive with excellent performances.

In Situ Compatibilization of Isotactic Polypropylene and High-Density Polyethylene by a Melt Cobranching Reaction

Incompatible polypropylene (PP) and polyethylene (PE) are difficult to separate in mixed recycling streams such as waste plastic packaging, which makes polyolefin mixtures unsuitable for high-quality products. In this work, based on the free radical branching reaction, a co-branching reaction of isotactic polypropylene (iPP) and high-density polyethylene (HDPE) blends was carried out in the presence of the peroxide, free radical regulator and multifunctional acrylate monomer, and a star-like long-chain branching (LCB) copolymer was obtained. The effect of in situ compatibilization on the structures and mechanical properties of iPP/HDPE was investigated, and the compatibilization mechanism was discussed. Results showed that the mechanical properties of the modified blends were largely improved, and efficient in-situ compatibilization of iPP and HDPE could be taken place in a wide process window. Moreover, the sizes of the dispersed phase in the modified blends were clearly decreased, and the interfacial thickness increased. Compared with the pure iPP/HDPE blend, the initial crystallization temperature of iPP in the modified iPP/HDPE blend was increased, and long branched chains of the LCB copolymers were physically entangled with the chemical identical homopolymers or even participated in the crystallization of iPP and HDPE. Thanks to the in situ compatibilization strategy, the compatibility of iPP/HDPE was significantly improved.

Polymerization Photoinitiators with Near-Resonance Enhanced Two-Photon Absorption Cross-Section: Toward High-Resolution Photoresist with Improved Sensitivity

We take advantage of the near-resonant enhancement of the third-order nonlinear response to engineer a two-photon polymerization photoinitiator with optimized efficiency in regard to literature benchmarks. We study in detail its linear and resonant third-order nonlinear optical properties, with particular focus on photoinduced radical generation. Careful choice of peripheral substituents enables its direct solubilization into a mixture of commercial multifunctional acrylic monomers, resulting in a homogeneous photoresist with good optical transparency upon simple mixing. When submitted to sub-nanosecond pulsed laser irradiation at 532 nm, the resulting photoresist displays a polymerization threshold up to eight times lower than that obtained with the classically used two-photon initiators, giving rise to sub-100 nm line width at 250 nm interline separation and resulting in highly defined three-dimensional structures.

On the Network Topology of Cross-Linked Acrylate Photopolymers: A Molecular Dynamics Case Study.

A reactive molecular dynamics approach is used to simulate cross-linking of acrylate polymer networks. By employing the same force field and reactive scheme and studying three representative multifunctional acrylate monomers, we isolate the importance of the nonreactive moieties within these model monomers. Analyses of reactive trajectories benchmark the estimated gel points, cyclomatic character, and spatially resolved cross-linking tendencies of the acrylates as a function of conversion. These insights into the similarities and differences of the polymerization and resulting networks suggest molecular mechanics as a useful tool in the rational design of photopolymerization resins.

Photosensitive Formulation for Additive Manufacturing-3D Printing

UV curing is a photochemical process in which high-intensity ultraviolet light is used to instantly cure or ��dry�� coatings, inks, adhesives and thin film technology. It has been around as a coating for wood, paper and as a clear coating via photolithography process on printed circuit boards PCBs or integrated circuit boards ICBs for years. It is fast becoming one of the most popular techniques in the paint and coatings industry. Most of the formulation use multifunctional acrylate monomers or oligomers or a mixture of them that crosslink under exposure to UV/EB radiations in a free radical process. We briefly present the advantages of EB vs. UV. A new type of formulation based on multifuctional monomer of dicyclopentadiene epoxy derivative with additional diluent as co-reactive solvent will be described and evaluated. This formulation differs from the acrylate one by the use of a cationic photoinitiator. The final product presents all the advantages of epoxy resins viz. better adherence, mechanical and thermal properties, compared to acrylate systems. Formulation has been optimized thanks to the differential scanning photocalorimetry DPC. This type of formulation is developed for additive digital manufacturing - 3D Printing (building layer by layer).

The effect of Poly(Ethylene oxide) cross-linking structure on the mechanical properties and CO2 separation performance of an ion gel membrane

Ionic liquid gels of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide plasticizing a cross-linked poly(ethylene oxide) are high performance CO2 separation membranes. Here, the effect of polymer cross-link density on the ionic liquid stability, on the mechanical properties of the resulting films, and on the gas separation properties were studied. Cross-link density was modified by changing the chain length of ethoxylated diacrylate and triacrylate monomers, and by incorporating small amounts of short, multifunctional acrylate monomers. Without the ionic liquid acting as permanent plasticizer, higher cross-link density is associated with higher yield strength but lower strain at break, as expected. In a plasticized network, however, the loss in flexibility is not accompanied by higher yield strength, leaving ion gels made from highly cross-linked network more fragile than those having longer, more flexible chains. Lowering cross-link density also allowed more ionic liquids to be incorporated as a phase stable gel and led to better CO2 separation performance.

Photo-stable cross-linked micron bead with functionalized quantum via suspension polymerization for color conversion

Acrylate groups were introduced on quantum dots (QD) via ligand exchange followed by nucleophilic reaction. The QDs were then polymerized with other multi-functional acrylic monomers in this study. Two acrylate groups were introduced at the end of an elongated ligand and the ligands with two acrylate groups were fully coordinated on the entire surface of the QD. This ligand modification scheme made the QDs highly reactive and also compatible with common organic solvents. No decrease in the quantum yield of the QDs was observed after ligand modification and the adduction reaction. The acrylate functional groups in the QDs were verified by 1H NMR and FT-IR. The prepared QDs with a terminal acrylate group were reacted with trimethylolpropane triacrylate and 1,6-hexanediol diacrylate to form micrometer scale beads via suspension polymerization. The diameter of the spherical beads was in the range of 80–150 μm and QDs 13 nm in diameter were found to be evenly dispersed in the polymer beads. The QD-polymer beads were applied to color conversion layers (CCL) on a blue light emitting diode (LED). The QD-polymer beads showed a 50% reduction over 72 h from the initial optical efficiency, while the QD embedded in the PMMA matrix (QD-PMMA) was reduced by 50% for 14 h.

The effect of cross-linking density on water vapor and oxygen permeability of hybrid UV cured nano coatings

In this study, the effect of cross-linking density of organic contents, precursor ratio and proportion of inorganic to organic phases on water and oxygen permeability of sol-gel based hybrid UV cured coating on biaxially oriented polypropylene (BOPP) substrate was evaluated. Multi-functional acrylic monomers including, Isobornyl acrlate (IBOA), Tripropylene glycol diacrylate (TPGDA), Trimethylol propane triacrylate (TMPTA), Di-penta-erythritol hexa-acrlate (DPHA) and tri-functional aliphatic urethan acrylate oligomer were used as organic phase, while inorganic phase contained tetraethyl orthosilicate (TEOS) and 3-methacryloxy propyltrimethoxy silane (MEMO) precursors. A mixture technique utilized as designing the experimental processes. A high cross-linked hybrid enhanced the barrier property and reduced considerably both the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of uncoated BOPP from 88 ± 0.89, to 0.88 ± 0.05 (g / m2.day) and from 2010 ± 26–317 ± 11 (cm3 / m2.day), respectively. It was observed that in constant TEOS to MEMO ratio (I/O = 50), by altering the ratio of inorganic /organic from 20 to 80 water vapor depreciated from 3.9 ± 0.10 to 0.88 ± 0.05 g/ (m2.d). These results were in agreement with the presence of a dense network. Phase images of atomic force microscopy analysis showed a homogenous distribution of inorganic particles in the organic network. The presence of a high cross-linked organic phase can replace the presence of 30% of an inorganic phase in hybrid coatings. The correlation between WVTR and the multiplication of the surface energy (ε) in the cross-linking density (ʋ) has shown that increasing the diffusion coefficient had considerable influence on reduction of WVTR than increasing the solubility coefficient.

Macroporous titania monoliths from emulsion templated composites

High internal phase emulsion (HIPE) templating approach, well known for the preparation of macroporous polymeric monoliths (polyHIPEs), was utilized for the synthesis of macroporous cellular interconnected titania ceramic monoliths. In order to derive the ceramic monolithic material from the precursor polymer, titania particles were introduced into the monomer containing emulsion phase. The morphology of the final ceramic monolith closely resembled the precursor polymer composite, featuring a 3D interconnected cellular structure with the first level of pores with an average diameter of 70–100 μm and channels connecting the first level of pores. Multifunctional acrylate monomer was used in a combination with photopolymerization for the preparation of composite polyacrylate/titania monolith. The ratio of particles to monomer and the temperature profile of sintering were the most important factors affecting the morphology of the final material. A significant increase in the modulus of the sintered material compared to the porous composite precursors was found.

Crosslinking gradients of a photopolymerized multifunctional acrylate film control mechanical properties

Photopolymerization of thin monomer films can be used to manufacture parts rapidly, but can lead to gradients of elastic modulus, particularly when the film is illuminated from only one side. In order to better understand the relationship between film curing (expressed in terms of carbon–carbon double bonds, C=C) and mechanical properties, a model was developed and tested against experimental results. The example system used in this work was a thin film microfluidics chip made from a multifunctional acrylate monomer. An 800-micron monomer film containing a photoinitiator was illuminated from the top surface, producing a solid chip. The C=C content and mechanical properties of the chip were measured at multiple positions over the cross sections. Raman spectroscopy was used to measure local C=C concentrations, and nanoindentation was used to measure local Young’s modulus and hardness. Spatial gradients in monomer conversion, Young’s modulus, and hardness were measured on a series of chips manufactured at different light doses. A photopolymerization model was used to fit the Raman data, providing quantitative predictions of the monomer conversion as a function of film depth and light dose. These data were then correlated with the values of Young’s modulus and hardness. The correlation between the photopolymerization and the mechanical properties can be used to optimize the mechanical properties of thin films within the manufacturing and energy constraints and should be scalable to other multifunctional monomer systems.

Peroxide-initiated graft modification of thermoplastic BioPolyesters: Introduction of long-chain branching

The chemical modification of polylactic acid (PLA) and related polyesters by peroxide-initiated grafting of multifunctional allylic and acrylic monomers is described. Solvent-free, melt-state reactions of PLA and triallyl trimesate (TAM) are shown to be remarkably efficient compared to analogous reactions of polyolefins such as poly(ethylene-co-octene) (EOC), requiring very low reagent loadings to produce a long chain branched (LCB) architecture. A systematic study of potential transesterification chemistry confirms that ionic reactions do not contribute significantly to PLA reactivity under typical grafting conditions. Further explorations of H-atom abstraction and monomer addition yields demonstrate that PLA is relatively unreactive toward the radical reactions that support LCB production. Careful examination of the solubility of coagent intermediates reveal dramatic differences in oligomer solubility between a hydrocarbon system and an ester-based matrix. Whereas TAM conversion in hydrocarbon leads to a precipitation polymerization that removes coagent from solution, reactions conducted in the polyester do not incur losses of oligomeric intermediates, indicating that the ability of PLA to retain multi-functional intermediates is the underlying cause of its remarkable LCB grafting yields.

A self-healing polysiloxane elastomer based on siloxane equilibration synthesized through amino-ene Michael addition reaction

A facile approach to synthesize silicone elastomers with good mechanical properties as well as high self-healing efficiency is reported in the present research. The silicone elastomer is synthesized through amino-ene Michael addition reaction, with amino groups from aminopropyl-terminated polydimethylsiloxane and acrylate groups from multifunctional acrylate monomer. Meanwhile, basic catalyst tetramethylammonium hydroxide is added into the elastomer to derive a dynamically crosslinked network. Tensile strength and break elongation of the synthesized elastomers are 1.08 ± 0.06 MPa and 206.10 ± 9.55%, respectively, indicating good mechanical properties of the elastomers. The fractured samples can recover 91% of their original strength after healing at 105 °C for 24 h. Moreover, the silicone elastomer in this work is recyclable due to the dynamic siloxane equilibration reaction.

Fabrication of Mechanically Strong Honeycombs with Aerogel Cores

Honeycomb aerogel composites were fabricated by reinforcing selected regions of a native aerogel matrix using photopolymerization. First, alcogels were synthesized by hydrolysis–condensation of a siloxane, and by adding a multifunctional acrylic monomer and a visible-light initiator to the gelation solution. Alcogels were then placed on a programmable translation stage and exposed to a laser. Polymerization and mechanical reinforcement were induced in the exposed regions. After exposure alcogels were dried supercritically. Thermal conductivity and out-of-plane modulus of the resulting honeycombs could be varied between values typical of native aerogels (11 mW/mK and 0.75 MPa) and those of uniformly polymerized composites (65.8 mW/mK and 36.26 MPa) by varying the translation stage speed between 2 and 3 mm/s. The results were interpreted using a rule-of-mixtures model. The mechanical properties of the composites were also investigated using finite element analysis.

Hyperbranched poly(ether amine) (hPEA) as novel backbone for amphiphilic one-component type-II polymeric photoinitiators

To make photoinitiators (PI) to be polymeric and water-soluble is an effective approach to develop the high efficient photoinitiator systems with low-migration, low-toxic and environment-friend. We developed a series of novel amphiphilic hyperbranched polymeric photoinitiators (hPEA-TXs, and hPEA-BPs) by introducing thioxanthone (TX) or benzophenone (BP) moieties into the periphery of the hyperbranched poly(ether amine) (hPEA) comprised of the hydrophilic poly(ethylene oxide) (PEO) short chain and coinitiator amine moieties in the backbone. Compared with their water-soluble low-molecular weight analogues, the resulting hyperbranched polymeric photoinitiators hPEA101-TX, hPEA211-TX, hPEA101-BP and hPEA211-BP could be dissolved very well not only in many organic systems including acrylate monomers, but also in water with high solubility of 10wt%. The photopolymerization kinetics of water-soluble monomer acrylamide (AM) and three hydrophobic multifunctional acrylate monomers initiated by these hyperbranched photoinitiators were investigated in detail by photo-differential scanning calorimetric (photo-DSC). Both hPEA-TXs and hPEA-BPs can initiate photopolymerization of AM as efficiently as their low-molecular weight analogues MGA-TX and MGA-BP, respectively. The final double bond conversion (DBC) of oil-soluble monomer hexanediol diacrylate (HDDA) photoinitiated by these hyperbranched photoinitiators can reach as high as 99%. Especially for photopolymerization of multifunctional monomers initiated by these hyperbranched polymeric photoinitiators, the final DBC of trimethylolpropane triacrylate (TMPTA) and pentaerythritol tetraacrylate (PETTA) can reach 80% and 60%, respectively, which is much higher than that of low-molecular weight photoinitiators.