Large diameter (> 100 mm) planar Na-β″-Al2O3 solid electrolytes (BASE) with thickness from 1.0 to 1.5 mm have been prepared. Na-β″-Al2O3 was processed as a slurry and cast to give several meters of tape. One hundred and forty mm diameter discs were punched from the tape, stacked, and laminated with a large hydraulic press. Binder burnout and sintering were performed in 150 mm diameter MgO spinel encapsulations to mitigate the loss of Na2O vapor. Conductivity and flexural strength were measured on smaller Na-β″-Al2O3 samples produced via the same tape casting process followed by sintering and gave results consistent with BASE materials produced by uniaxial pressing of powders. Planar BASE membranes enable new cell designs, which are predicted to have higher power densities and better stacking efficiency compared to currently manufactured tubular cells.

High temperature Na2O vapor conversion of alpha-Al2O3 with different concentrations of yttria stabilized zirconia (YSZ) was used to produce Na-beta ''-Al2O3 solid electrolyte (BASE) materials. The influence of different ratios of yttria (YSZ-3 and YSZ-8) on conversion and material properties (ionic conductivity and flexural strength) was also investigated. Extent of conversion to Na-beta ''-Al2O3 was calculated by semi-quantitative XRD phase analysis. Al2O3 composites with 20% or less YSZ were incompletely converted to Na-beta ''-Al2O3 after 2 h at 1450 degrees C. Al2O3 composites with 30-40% YSZ-3 appear fully converted by XRD but have lower conductivity and higher strength compared to conventionally sintered Na-beta ''-Al(2)O(3 )composites with the same concentration of YSZ-3. SEM of the materials indicated differences in morphology and grain size. XRD of Al2O3 composites with YSZ-8 showed significantly lower conversion than those with YSZ-3. This is attributed to the larger grain size of YSZ-8, which limits the homogeneity of composites with Al2O3 and thus does not assist in oxygen diffusion as well as YSZ-3. Although the vapor converted BASE materials tended to have lower conductivities at 300 degrees C, they have lower activation energies (0.20 eV) compared to conventionally sintered Na-beta ''-Al2O3 composites (0.30 eV) and comparatively higher conductivity at ambient temperature. Vapor converted BASE materials also have better mechanical properties, which should allow fabrication of thinner electrodes.

Free standing single layer silicon carbonitride components with sub-mm features have been constructed by maskless lithography followed by pyrolysis. In comparison to prior fabrication methods based on molding of ceramic precursors, this work is advantageous as crosslinked polymer green bodies are formed in a direct manner and no mold is needed. The resultant silazane green bodies are pyrolyzed in argon to give SiCN ceramics. Mechanical properties of test samples created via the same process indicate typical flexural strength of 890 MPa and hardness of 1550 HV1.0. This methodology should be of general interest for the production of silicon carbide and silicon carbonitride components for various MEMS applications.

Freestanding SiCNO ceramic pieces with sub-mm features were produced by laser crosslinking of carbosilane and silazane polymer precursors followed by pyrolysis in inert atmosphere. Three different pulsed UV laser systems were investigated, and the influence of laser wavelength, operating power and scanning speed were all found to be important. Different photoinitiators were tested for the two lasers operating at 355 nm, while for the 266 nm laser, crosslinking occurred also without photoinitiator. Pre-treatment of glass substrates with fluorinated silanes was found to ease the release of green bodies during solvent development. Polymer crosslinking was observed with all three of the laser systems, as were bubbles, surface charring and in some cases ablation. By focusing the laser beam several millimeters above the surface of the resin, selective polymer crosslinking was observed exclusively.

With the aim of modifying the composition and microstructure of SiC and SiCN ceramics, we have investigated different reactive additives for polymer derived ceramic (PDC) precursors as well as changes in processing conditions (polymerization conditions, sintering conditions, etc.). Different concentrations of additive were dispersed in commercial carbosilane and silazane resins to give preceramic composites, which were pyrolyzed to ceramics. By adjusting the ratio of additive, the microstructure of resultant ceramics was affected as are the electrical and mechanical properties.

Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.

Photo-curable resins based on multifunctional acrylate monomers are commonly applied as thin films (e.g. protective coatings, printing inks, etc.) and in recent years are also used for the fabrication of bulk objects such as dental fillings and 3D-printed parts. While rapid curing and good spatial resolution are advantages to these systems, brittleness and poor impact resistance due to inhomogeneous polymer architecture and high crosslink density are serious drawbacks. By comparison, epoxy thermoset resins suffered many years ago from similar problems, but since then are found in ever demanding applications thanks to a variety of approaches to increase polymer toughness. Based on these successes, researchers have tried to translate strategies for toughening epoxy resins to photopolymer networks. Therefore, this review surveys relevant scientific papers and patents on the development of crosslinked epoxy-based polymers and also photo-curable polymers based on multifunctional acrylates with improved toughness. Strategies developed to reduce brittleness include working with monomers, which intrinsically give tougher polymers, particulate additives, and alternate forms of polymerization and polymer architecture (e.g., dual-cure networks, interpenetrating networks, thiol-ene chemistry). All of these strategies have advantages and yet application specific rigours must also be considered before and during formulation development.

ABSTRACTThe rapid and uncontrolled nature of network formation from di(meth)acrylate monomers produces high shrinkage stress and results in polymers with oftentimes brittle mechanical properties. Methods for regulating polymerization and network formation are sought. One option is the use of addition–fragmentation chain transfer (AFCT) agents, which are well known to control molecular weight and molecular weight distribution of monofunctional (meth)acrylates. A series of novel and previously described AFCT reagents were synthesized and screened with laser flash photolysis to determine reactivity. Well‐performing AFCT reagents were then tested in polymerizations with monofunctional and difunctional methacrylates. With monofunctional monomers, the molecular weight and polydispersity of the resultant linear polymers tend to decrease with the addition of AFCT agent. In copolymerization with dimethacrylate monomers, the AFCT agents were found to substantially lower and sharpen the glass transition. Sharpness of the glass transition is here indicative of a more regular and homogenous network. After coupling of the instruments, photorheology was performed simultaneously with real‐time IR to show an increase in monomer conversion at the time of gelation, which appears to have a positive effect on reducing shrinkage stress. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 394–406

In radical polymerization of monofunctional monomers, addition fragmentation chain transfer (AFCT) agents are well known to regulate polymerization and yield polymers with lower molecular weights and narrower molecular weight distributions. Papers concerning bulk photopolymerization of monomer mixtures with AFCT agents are rarely found in literature. In this article, AFCT reagents based on β-allyl sulfones with different vinyl activating groups were synthesized and compared. The compounds were tested in mono- and difunctional monomer systems providing information about the influence on photoreactivity, molecular weight, as well as thermal and mechanical properties of the resultant polymers. Where more potent activating groups (-Ph, -CN) markedly influenced polymerization at lower concentrations, the AFCT reagent with an ester activating group reacted at a similar rate to the methacrylate monomer (CT ≈ 1) and provided the best overall performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1417-1427

Ionic liquid (IL) monomers are receiving increased attention due to their versatile range of application, especially in the electrochemical and electromechanical fields. Within this study, imidazole-based ILs containing a polymerizable methacrylate (MA) group were synthesized to examine their influence on the viscosity and reactivity of typical (meth)acrylates. The IL-MAs were prepared from 1-butylimidazole and bromo methacrylates with different spacer lengths (C2–C6). The best results with respect to physicochemical properties and double bond conversions could be obtained for ILs with C3 and C6 spacers. Bulk polymerizations exhibited unusually high reactivity and double-bond conversion compared with typical mono-methacrylates. Addition of 10 wt% IL-MA to reactive diluents like hexane-1,6-diol diacrylate caused only minor reduction in reaction rate but increased final double bond conversion compared with the pure diacrylate.

Photo-curing has become increasingly popular in wood coating applications relative to thermally initiated processes due to increased curing rate with reduction in solvent and energy requirements. Stressing the last advantage, light emitting diodes (LEDs) utilize less energy and last longer than traditional Hg lamps and are commercially available now in wavelengths below 400 nm. Although photo-curing does have its advantages, an additional difficulty is encountered when this is performed in open-air since molecular oxygen inhibits radical polymerization. This leads to insufficiently cured films that remain tacky at the surface. Although nitrogen gas inerting can be highly successful in excluding oxygen, chemical additives are often preferable to the small and medium-sized enterprise (SME) end user. A variety of additives have been introduced over the last 30 years both in the scientific and patent literature. We have chosen to experimentally reinvestigate the applicability of some of these additives (hydrogen donors, functional monomers, reducing agents, CO2 producing agents, and singlet oxygen scavengers). applying them to a urethane acrylate base formulation. Curing was performed with LED irradiation and effectiveness assessed by FTIR in transmission mode. (C) 2014 Elsevier B.V. All rights reserved.

Thiol-Ene polymerization has gained ever increasing interest during the last decade. Advantages such as low oxygen inhibition and shrinkage, uniform networks with significantly improved mechanical properties are accompanied by up to now unsolved disadvantages such as unpleasant odor and poor storage stability. We have addressed the latter issue with twocomponent stabilizer systems that provide thiol-(meth)acrylate compositions with nearly no increase in viscosity after one year. We have also explored the advantages of thiols to help increase the reactivity of vinyl esters and vinyl carbonates. These monomers are low toxic alternatives to acrylates that are not only suitable for biomedical applications but also for classical coatings. Copolymerization of vinyl carbonates and vinyl esters with diand tetrathiol monomers is shown to proceed at rates intermediate to (meth)acrylates. Material properties are strongly influenced by degree of crosslinking. Processing of these novel thiolene compounds by multiple modes of photo-based AMT will also be presented.

Branislav Husár/Institute of Applied Synthetic Chemistry, Vienna University of Technology/Vienna, Austria Samuel Clark Ligon/Institute of Applied Synthetic Chemistry, Vienna University of Technology/Vienna, Austria Harald Wutzel/Institute of Applied Synthetic Chemistry, Vienna University of Technology/Vienna, Austria Helmuth Hoffmann/Institute of Applied Synthetic Chemistry, Vienna University of Technology/Vienna, Austria Robert Liska/Institute of Applied Synthetic Chemistry, Vienna University of Technology/Vienna, Austria

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTStrategies to Reduce Oxygen Inhibition in Photoinduced PolymerizationSamuel Clark Ligon†, Branislav Husár†‡, Harald Wutzel†, Richard Holman§, and Robert Liska*†View Author Information† Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163/MC, A-1060 Vienna, Austria‡ Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava 45, Slovakia§ The Paint Research Association, 14 Castle Mews, High Street, TW12 2NP Hampton, United Kingdom*E-mail: [email protected]Cite this: Chem. Rev. 2014, 114, 1, 557–589Publication Date (Web):October 1, 2013Publication History Received9 January 2013Published online1 October 2013Published inissue 8 January 2014https://doi.org/10.1021/cr3005197Copyright © 2013 American Chemical SocietyRequest reuse permissionsArticle Views14144Altmetric-Citations483LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (5 MB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Inhibition,Monomers,Organic compounds,Oxygen,Polymerization Get e-Alerts

The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to their complicated syntheses often reliant on expensive catalysts. These shortcomings have been a critical obstruction for further advances in the promising field of two-photon-induced photopolymerization (TPIP) technology. This paper describes a series of linear and cyclic benzylidene ketone-based two-photon initiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure-activity relationships were conducted via quantum-chemical calculations and experimental tests. These results showed that the size of the central ring significantly affected the excited state energetics and emission quantum yields as well as the two-photon initiation efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much broader ideal processing windows than its counterparts with a central five-membered ring and previously described highly active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization.

Engineering three-dimensional (3D) hydrogels with well-defined architectures has become increasingly important for tissue engineering and basic research in biomaterials science. To fabricate 3D hydrogels with (sub)cellular-scale features, two-photon polymerization (2PP) shows great promise although the technique is limited by the selection of appropriate hydrogel precursors. In this study, we report the synthesis of gelatin hydrolysate vinyl esters (GH-VE) and its copolymerization with reduced derivatives of bovine serum albumin (acting as macrothiols). Photorheology of the thiol-ene copolymerization shows a much more rapid onset of polymerization and a higher end modulus in reference to neat GH-VE. This allowed 2PP to provide well-defined and stable hydrogel microstructures. Efficiency of the radical-mediated thiol-vinyl ester photopolymerization allows high 2PP writing speed (as high as 50 mm s(-1)) with low laser power (as low as 20 mW). MTT assays indicate negligible cytotoxicities of the GH-VE macromers and of the thiol-ene hydrogel pellets. Osteosarcoma cells seeded onto GH-VE/BSA hydrogels with different macromer relative ratios showed a preference for hydrogels with higher percentage of GH-VE. This can be attributed both to a favorable modulus and preferable protein environment since gelatin favors cell adhesion and albumin incurs nonspecific binding. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4799-4810

Monomers for radical photopolymerization based on vinyl esters (VEs) have recently been identified as suitable alternatives to (meth)acrylates on account of their low irritancy and cytotoxicity. The drawback of most VEs with abstractable hydrogens is their relatively low reactivity compared with (meth)acrylates. Within this article, we proved by photo-differential scanning calorimetry measurements and real-time Fourier transform infrared spectroscopy that the thiol-ene concept is able to improve the photoreactivity of these VEs to a large extent to a level between those of acrylates and methacrylates. Other VEs have now a reactivity of at least the level of similar acrylates. Mechanical properties as determined by Dynamic Mechanical Analysis and Charpy impact tests showed significant toughening of these materials. Furthermore, we were able to confirm low toxicity of all components by osteoblast cell culture experiments. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Various phenolic radical inhibitors were tested to improve storage stability of thiol-ene formulations. After determining the optimal inhibitor, a synergetic effect was discovered when it was used in combination with acidic buffer, thus preventing premature dark gelation while maintaining desired photoreactivity. Additional Supporting Information may be found in the online version of this article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.