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We prove that a plethysm product of two Schur functions can be factorised uniquely and classify homogeneous and indecomposable plethysm products.

Objective Dental restorative composites have been extensively studied with a goal to improve material performance. However, stress induced microcracks from polymerization shrinkage, thermal and other stresses along with the low fracture toughness of methacrylate-based composites remain significant problems. Herein, the study focuses on applying a dynamic covalent chemistry (DCC)-based adaptive interface to conventional BisGMA/TEGDMA (70:30) dental resins by coupling moieties capable of thiol–thioester (TTE) DCC to the resin–filler interface as a means to induce interfacial stress relaxation and promote interfacial healing. Methods Silica nanoparticles (SNP) are functionalized with TTE-functionalized silanes to covalently bond the interface to the network while simultaneously facilitating relaxation of the filler–matrix interface via DCC. The functionalized particles were incorporated into the otherwise static conventional BisGMA/TEGDMA (70:30) dental resins. The role of interfacial bond exchange to enhance dental composite performance in response to shrinkage and other stresses, flexural modulus and toughness was investigated. Shrinkage stress was monitored with a tensometer coupled with FTIR spectroscopy. Flexural modulus/strength and flexural toughness were characterized in three-point bending on a universal testing machine. Results A reduction of 30% in shrinkage stress was achieved when interfacial TTE bond exchange was activated while not only maintaining but also enhancing mechanical properties of the composite. These enhancements include a 60% increase in Young’s modulus, 33% increase in flexural strength and 35% increase in the toughness, relative to composites unable to undergo DCC but otherwise identical in composition. Furthermore, by combining interfacial DCC with resin-based DCC, an 80% reduction of shrinkage-induced stress is observed in a thiol–ene system “equipped” with both types of DCC mechanisms relative to the composite without DCC in either the resin or at the resin–filler interface. Significance This behavior highlights the advantages of utilizing the DCC at the resin–filler interface as a stress-relieving mechanism that is compatible with current and future developments in the field of dental restorative materials, nearly independent of the type of resin improvements and types that will be used, as it can dramatically enhance their mechanical performance by reducing both polymerization and mechanically applied stresses throughout the composite lifetime.

Objective To assess the performance of thiol Michael photocurable composites based on ester-free thiols and vinyl sulfonamides of varying monomer structures and varied filler loadings and to contrast the properties of the prototype composites with conventional BisGMA-TEGDMA methacrylate composite. Methods Synthetic divinyl sulfonamides and ester-free tetrafunctional thiol monomers were utilized for thiol-Michael composite development with the incorporation of thiolated microfiller. Polymerization kinetics was investigated using FTIR spectroscopy. Resin viscosities were assessed with rheometry. Water uptake properties were assessed according to standardized methods. Thermomechanical properties were analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were measured on a universal testing machine in three-point bending testing mode. Results The vinyl sulfonamide-based thiol-Michael resin formulation demonstrated a wide range of viscosities with a significant increase in the functional group conversion when compared to the BisGMA-TEGDMA system. The two different types of vinyl sulfonamide under investigation demonstrated significant differences towards the water sorption. Tertiary vinyl sulfonamide did not undergo visible swelling whereas the secondary vinyl sulfonamide composite swelled extensively in water. With the introduction of rigid monomer into the polymer matrix the glass transition temperature increased and so increased the toughness. Glassy thiol-Michael composites were obtained by ambient curing. Significance Employing the newly developed step-growth thiol-Michael resins in dental composites will provide structural uniformity, improved stability and lower water sorption.

A spiropyran-containing triazole-phosphatidylcholine (SPTPC) was synthesized through a copper-catalyzed azide alkyne cyclo-addition (CuAAC) reaction. In water, SPTPCs self-assembled and a spontaneous spiropyran-to-merocyanine (SP-to-MC) isomerization occurred, resulting in coexistence of liposomes and fibers, and switching from the spiropyran (SP) to the merocyanine (MC) isomeric structure induced a reversible transition between these molecular assemblies. Study of the self-assembly of SPTPCs and photo-induced liposome–fiber assembly-transition revealed that the presence of MC enabled additional inter-membrane interaction during self-assembly and that the MC-stacking effect was the driving force for the assembly-transition. Exposure to UV light induced switching from SP to MC, where the planar structure of MC and the confinement of MC led to enhanced MC-stacking. The effect of MC-stacking was both advantageous and disadvantageous: MC-stacking perturbed the hydrophobic phase in the bilayer membrane and facilitated the liposome-to-fiber transition, otherwise the MC-stacking retarded switching of MC to SP, and caused an incomplete recovery of MC to SP during fiber-to-liposome recovery, thus a fatigue of SP was induced by MC-stacking during the liposome-to-fiber transition cycle. To decrease the intermolecular interactions and suppress MC-stacking, photo-inert triazole-phosphatidylcholine (TPC) was incorporated to prepare two-component TPC/SPTPC-liposomes, which exhibited better recovery kinetics. The photo-adaptive behavior of TPC/SPTPC-liposomes confirmed the disturbance of bilayer membranes by inter-membrane MC-stacking and the formation of MCTPC-enriched phases in the bilayer membrane.

Two-stage holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10–2 enable the fabrication of a myriad of optical elements. While there are commercial products available that meet these requirements, researchers often want the flexibility to customize both the form factor of the samples as well as the mechanical and chemical properties for their specific applications. We present a novel high refractive index acrylate writing monomer in a low refractive index urethane matrix as a model material for customization for optical applications. We discuss the achievable Δn of this custom monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA) in the urethane matrix as a function of solubility, along with a comparison to a commercially available high refractive index monomer, 2,4,6- tribromophenyl acrylate. Formulations with BPTPA exhibit a peak-to-mean Δn ≈ 0.029 in transmission holograms without any obvious deficiencies in transparency, color, or scatter. This writing monomer and the synthetic processes present a promising platform for the fabrication of high-performance holographic photopolymers for a wide range of research applications.

International Atomic Energy Agency Nuclear FusionPAPER • THE FOLLOWING ARTICLE ISOPEN ACCESSMultiphysics analysis with CAD-based parametric breeding blanket creation for rapid design iterationJonathan Shimwell1, Rémi Delaporte-Mathurin2, Jean-Charles Jaboulay3, Julien Aubert3, Chris Richardson4, Chris Bowman5, Andrew Davis1, Andrew Lahiff1, James Bernardi6, Sikander Yasin7,8Show full author listPublished 8 March 2019 • © EURATOM 2019Nuclear Fusion, Volume 59, Number 4Citation Jonathan Shimwell et al 2019 Nucl. Fusion 59 046019DOI 10.1088/1741-4326/ab0016DownloadArticle PDFFiguresReferencesDownload PDF2222 Total downloads1111 total citations on Dimensions.Article has an altmetric score of 9Turn on MathJaxShare this articleShare this content via emailShare on Facebook (opens new window)Share on Twitter (opens new window)Share on Mendeley (opens new window)Article informationAbstractBreeding blankets are designed to ensure tritium self-sufficiency in deuterium–tritium fusion power plants. In addition to this, breeder blankets play a vital role in shielding key components of the reactor, and provide the main source of heat which will ultimately be used to generate electricity. Blanket design is critical to the success of fusion reactors and integral to the design process. Neutronic simulations of breeder blankets are regularly performed to ascertain the performance of a particular design. An iterative process of design improvements and parametric studies are required to optimize the design and meet performance targets. Within the EU DEMO program the breeding blanket design cycle is repeated for each new baseline design. One of the key steps is to create three-dimensional models suitable primarily for use in neutronics, but could be used in other computer-aided design (CAD)-based physics and engineering analyses. This article presents a novel blanket design tool which automates the process of producing heterogeneous 3D CAD-based geometries of the helium-cooled pebble bed, water-cooled lithium lead, helium-cooled lithium lead and dual-coolant lithium lead blanket types. The paper shows a method of integrating neutronics, thermal analysis and mechanical analysis with parametric CAD to facilitate the design process. The blanket design tool described in this paper provides parametric geometry for use in neutronics and engineering simulations. This paper explains the methodology of the design tool and demonstrates use of the design tool by generating all four EU blanket designs using the EU DEMO baseline. Neutronics and heat transfer simulations using the models have been carried out. The approach described has the potential to considerably speed up the design cycle and greatly facilitate the integration of multiphysics studies.

Biofabrication allows for the templating of structural features in materials on cellularly-relevant size scales, enabling the generation of tissue-like structures with controlled form and function. This is particularly relevant for growing organoids, where the application of biochemical and biomechanical stimuli can be used to guide the assembly and differentiation of stem cells and form architectures similar to the parent tissue or organ. Recently, ablative laser-scanning techniques was used to create 3D overhang features in collagen hydrogels at size scales of 10–100 µm and supported the crypt-villus architecture in intestinal organoids. As a complementary method, providing advantages for high-throughput patterning, we printed thioester functionalized poly(ethylene glycol) (PEG) elastomers using digital light processing (DLP) and created sacrificial, 3D shapes that could be molded into soft (G′ < 1000 Pa) hydrogel substrates. Specifically, three-arm 1.3 kDa PEG thiol and three-arm 1.6 kDa PEG norbornene, containing internal thioester groups, were photopolymerized to yield degradable elastomers. When incubated in a solution of 300 mM 2-mercaptoethanol (pH 9.0), 1 mm thick 10 mm diameter elastomer discs degraded in µm, resolutions of 22 ± 5 µm, and overhang structures as small as 50 µm, were printed on the order of minutes. These sacrificial thioester molds with physiologically relevant features were cast-molded into Matrigel and subsequently degraded to create patterned void spaces with high fidelity. Intestinal stem cells (ISCs) cultured on the patterned Matrigel matrices formed confluent monolayers that conformed to the underlying pattern. DLP printed sacrificial thioester elastomer constructs provide a robust and rapid method to fabricate arrays of 3D organoid-sized features in soft tissue culture substrates and should enable investigations into the effect of epithelial geometry and spacing on the growth and differentiation of ISCs.

A new addition-fragmentation chain transfer (AFT) capable moiety was incorporated into a dimethacrylate monomer that participated readily in network formation by copolymerizing with multifunctional methacrylates or acrylates. The process of AFT occurred simultaneously with photopolymerization of the AFT monomer (AFM) and other (meth)acrylate monomers leading to polymer stress relaxation via network reconfiguration. At low loading levels of the AFM, a significant reduction in shrinkage stress, especially for acrylate monomers, was observed with nominal effects on conversion. At higher loading levels of the AFM, the photopolymerization reaction kinetics and final double bond conversion were significantly lowered along with a delay in the gel-point conversion. Electron paramagnetic resonance studies during polymerization revealed the presence of a distinct radical species that was present in proportional quantities to the AFM content in the system. The lifetime and the character of the persistent radicals were altered due to the presence of the distinctive radical, in turn affecting the polymerization kinetics. With polymerization conducted at higher irradiance, the differential conversion between the control resin and samples with moderate AFM content was minimal, especially for the methacrylate-based formulations.

Here, we introduce photocuring as a tool for the spatiotemporal control of vitrimer network synthesis via a photoinitiated thiol–ene polymerization. A difunctional norbornene monomer was synthesized containing ester linkages and pendant alcohol groups to participate in transesterification bond reshuffling reactions. The transesterification catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was shown to be highly effective in promoting transesterification in these networks at high temperatures, without interfering with external spatiotemporal, photoinitiated control over the thiol–ene polymerization and associated network formation. A strong Arrhenius dependence of the stress relaxation time with inverse temperature was observed from 145 to 175 °C, which suggests a relaxation controlled by the transesterification reaction rate, similar to previously studied thermally cured vitrimers. These thiol–ene vitrimers are implemented in nanoimprint lithography (NIL) for creating surface features, where imprinting m...

We report the synthesis of polymeric particles using radical mediated step-growth thiol-ene and thiol-yne ‘click’ dispersion polymerizations in alcoholic solvents. Various alkene, alkyne and thiol monomers were used, and thermal, photo- or redox initiation methods were all shown to be effective means to initiate polymerization. Polymer particles typically were formed with diameters in the range of several hundred nanometers, with narrow size distributions though broader than typical free-radical chain-growth dispersion polymerizations. Photoinitiation yielded the smallest sizes due to the rapid nucleation of particles as compared to redox and thermal initiation methods. Reaction kinetics were monitored by FT-IR spectroscopy for aliquot samples taken at various reaction durations. The reaction achieved full conversion in photoinitiated systems within five minutes, while it took three hours for both thermal and redox initiation to be completed. The effects of polymerization conditions on particle size particularly the impact of monomer, stabilizer, and initiator concentrations were studied. Generally, average particle size increased with higher monomer concentration and decreased with additional stabilizer or initiator. Combinations of monomers with varying number of functional groups were investigated to form particles of various mechanical and physical behavior, including both linear and crosslinked systems.

We demonstrate the formation of shape-programmed, glassy origami structures using a single-layer photopolymer with two mechanically distinct phases. The latent origami pattern consisting of rigid, high cross-link density panels and flexible, low cross-link density creases is fabricated using a series of photomask exposures. Strong optical absorption of the polymer formulation creates depth-wise gradients in the cross-link density of the creases, enforcing directed folding which enables programming of both mountain and valley folds within the same sheet. These multiple photomask patterns can be sequentially applied because the sheet remains flat until immersed into a photopolymerizable monomer solution that differentially swells the polymer to fold and form the origami structure. After folding, a uniform photoexposure polymerizes the absorbed solution, permanently fixing the shape of the folded structure while simultaneously increasing the modulus of the folds. This approach creates sharp folds by mimicking the stiff panels and flexible creases of paper origami while overcoming the traditional trade-off of self-actuated materials that require low modulus for folding and high modulus for mechanical robustness. Using this process, we demonstrate a waterbomb base capable of supporting 1500 times its own weight.

A kinetic mechanism and the accompanying mathematical framework are presented for base-mediated thiol–Michael photopolymerization kinetics involving a photobase generator. Here, model kinetic predictions demonstrate excellent agreement with a representative experimental system composed of 2-(2-nitrophenyl)propyloxycarbonyl-1,1,3,3-tetramethylguanidine (NPPOC-TMG) as a photobase generator that is used to initiate thiol–vinyl sulfone Michael addition reactions and polymerizations. Modeling equations derived from a basic mechanistic scheme indicate overall polymerization rates that follow a pseudo-first-order kinetic process in the base and coreactant concentrations, controlled by the ratio of the propagation to chain-transfer kinetic parameters (kp/kCT) which is dictated by the rate-limiting step and controls the time necessary to reach gelation. Gelation occurs earlier as the kp/kCT ratio reaches a critical value, wherefrom gel times become nearly independent of kp/kCT. The theoretical approach allowed determining the effect of induction time on the reaction kinetics due to initial acid–base neutralization for the photogenerated base caused by the presence of protic contaminants. Such inhibition kinetics may be challenging for reaction systems that require high curing rates but are relevant for chemical systems that need to remain kinetically dormant until activated although at the ultimate cost of lower polymerization rates. The pure step-growth character of this living polymerization and the exhibited kinetics provide unique potential for extended dark-cure reactions and uniform material properties. The general kinetic model is applicable to photobase initiators where photolysis follows a unimolecular cleavage process releasing a strong base catalyst without cogeneration of intermediate radical species.

Synthetic vesicles have a wide range of applications from drug and cosmetic delivery to artificial cell and membrane studies, making simple and controlled formation of vesicles a large focus of the field today. Here, we report the use of the photoinitiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using visible light to introduce spatiotemporal control into the formation of vesicles. Upon the establishment of the spatiotemporal control over vesicle formation, it became possible to adjust initiation conditions to modulate vesicle sizes resulting in the formation of controllably small or large vesicles based on light intensity or giant vesicles when the formation was initiated in flow-free conditions. Additionally, this photoinitiated method enables vesicle formation at a density 400-fold higher than initiation using sodium ascorbate as the catalyst. Together, these advances enable the formation of high-density, controlled size vesicles using low-energy wavelengths while producing enhanced control over the formation characteristics of the vesicle.

Polysulfide network oxidative modification is presented. Fundamental differences between the properties of sufide-based and sulfone-based networks are discussed, and a method for producing the sulfone-based materials from thioether-based materials is developed. Oxidation enables significant mechanical property enhancements of polysulfide materials without any deleterious effects that typically accompany cross-linking polymerizations. Various application examples such as sulfide-containing particle modification and hardening of soft lithography or thiol–ene 3D microprinted objects are also shown.

Remote transport of material is an utmost useful, but challenging, property expanding the design possibilities of many applications such as microfluidics or robotics where species can be carried without interfering with its environment. Nature has solved the problem of transport in e.g., the respiratory system by a concerted motion of cilia. This study addresses a new method to fabricate an array of small parallel fibers acting as cilia placed side by side on a substrate. The fibers consist of a crosslinked liquid crystal main chain polymer functionalized with coreactant azobenzene molecules. The fibers bend toward a light source in a concerted manner. When placed in a liquid, the cooperative bending motion of the fibers creates a flow able to efficiently carry objects. The proposed fabrication process of the fibers is scalable to large area and requires an optimized rheology which is achieved by converting low molecular weight reactive liquid crystal acrylate monomers to oligomers using a multiplication of the monomeric units by the Michael addition reaction with dithiol. The oligomer properties and the elasticity of the fibers are adjusted by changing the thiol spacer leading to optimized manufacturing and maximized optical response.

In this letter, we present a robust covalent adaptable network (CAN) that relies on dynamic, exchangeable thiourethanes. A primary aliphatic isocyanate, hexamethylene diisocyanate (HDI), and a primary aliphatic thiol, ethoxylated-trimethylolpropane tri(3-mercaptopropionate) (EETMP), are employed to form a network that can fully relieve an applied stress at 90 °C in under 40 min through the thiourethane bond exchange with a low loading (1 mol%) of catalyst, 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). Based on the kinetic behavior of the dynamic chemistry, and as monitored via real-time FT-IR, synergetic dissociation and association mechanisms of the thiourethane bond exchange are proposed to explain the higher catalyst efficiency of the combined basic and nucleophilic catalyst, DBN, as compared to the strong basic catalyst, potassium tert-butoxide, and the strong nucleophilic catalyst, N-hetero carbene. Moreover, this thiourethane network exhibits excellent reprocessablity under relatively mild conditions (110 °C), which makes it a promising potential alternative to urethane materials in industry.

We present a thermally initiated thiol-Michael reaction based on initiation via the temperature-dependent thiol-TEMPO oxidation-reduction reaction. In the presence of a thiol, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, pK(a) = 5.5) is reduced to produce a much stronger base, i.e., tetramethylpiperidine (TMP, pK(a) = 11.4) in a temperature dependent process. This oxidation-reduction process is dramatically accelerated at elevated temperature, which allows for thermally controlled initiation of the base-catalyzed thiol-Michael addition reaction and potentially other base-catalyzed reaction systems. Several critical factors that affect base generation from TEMPO reduction were investigated via systematic variation of reaction conditions including the solvent, temperature, and the thiol type and concentration. The highly temperature-dependent attributes of this redox reaction were demonstrated in various thiol-TEMPO based systems and were further utilized to thermally control thiol-Michael polymerizations under different heating conditions. The strong amine species, TMP, formed at elevated temperatures from the TEMPO-thiol interaction combined with high temperature, enables rapid formation of thiol-Michael-based polymer networks and large scale material preparation without any detrimental effects often associated with highly exothermic polymerizations. This novel approach to develop thermally-initiated thiol-Michael polymer networks is unique, versatile and robust, resulting in wide utility in applications such as facile handling of highly reactive resins, bulk material preparation, pH sensitive materials construction, and composite/macro-particle synthesis.

The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, to exploratory plasmas driven by theoretical insight, exploiting the device's unique shaping capabilities. Disruption avoidance by real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic and radiation triggers. Runaway generation with high-Z noble-gas injection and runaway dissipation by subsequent Ne or Ar injection were studied for model validation. The new 1 MW neutral beam injector has expanded the parameter range, now encompassing ELMy H-modes in an ITER-like shape and nearly non-inductive H-mode discharges sustained by electron cyclotron and neutral beam current drive. In the H-mode, the pedestal pressure increases modestly with nitrogen seeding while fueling moves the density pedestal outwards, but the plasma stored energy is largely uncorrelated to either seeding or fueling. High fueling at high triangularity is key to accessing the attractive small edge-localized mode (type-II) regime. Turbulence is reduced in the core at negative triangularity, consistent with increased confinement and in accord with global gyrokinetic simulations. The geodesic acoustic mode, possibly coupled with avalanche events, has been linked with particle flow to the wall in diverted plasmas. Detachment, scrape-off layer transport, and turbulence were studied in L- and H-modes in both standard and alternative configurations (snowflake, super-X, and beyond). The detachment process is caused by power 'starvation' reducing the ionization source, with volume recombination playing only a minor role. Partial detachment in the H-mode is obtained with impurity seeding and has shown little dependence on flux expansion in standard single-null geometry. In the attached L-mode phase, increasing the outer connection length reduces the in-out heat-flow asymmetry. A doublet plasma, featuring an internal X-point, was achieved successfully, and a transport barrier was observed in the mantle just outside the internal separatrix. In the near future variable-configuration baffles and possibly divertor pumping will be introduced to investigate the effect of divertor closure on exhaust and performance, and 3.5 MW ECRH and 1 MW neutral beam injection heating will be added., This work was supported in part by the Swiss National Science Foundation.

Shortly after its inception, nanoimprint lithography (NIL) was primarily used as tool for the thermal embossing and flash curing of thermoplastic resists and polymer precursors, respectively. Driven by a need for high density material architectures, the semi-conductor industry served as the primary inspiration for NIL development for decades. However, as new resist materials have been explored, the variety of fields investing resources into the technology has grown, and NIL now finds applications actuating numerous organic and inorganic materials, imparting unique manifestations of elastic and plastic deformations. From photovoltaics to water filtration, the role of NIL is growing steadily, and this review illustrates the breadth of its impacts.

Christopher Bowman, Filip Du Prez and Julia Kalow introduce the Polymer Chemistry themed collection on chemistry for covalent adaptable networks.

The synthesis of thiolactone monomers that mimic natural nucleosides and engage in robust ring opening polymerizations (ROP) is herein described. As each repeat unit contains a thioester functional group, dynamic rearrangement of the polymer is feasible via thiol-thioester exchange, demonstrated here by depolymerization of the polymers and coalescing of two polymers of different molecular weight or chemical composition. This approach constitutes the first step toward a platform that enables for the routine synthesis of sequence controlled polymers via dynamic template directed synthesis.

Due to the ability to generate oligomers of precise sequence, sequential and stepwise solid-phase synthesis has been the dominant method of producing DNA and other oligonucleotide analogues. The requirement for a solid support, however, and the physical restrictions of limited surface area thereon significantly diminish the efficiency and scalability of these syntheses, thus, negatively affecting the practical applications of synthetic polynucleotides and other similarly created molecules. By employing the robust photoinitiated thiol-ene click reaction, we developed a new generation of clickable nucleic acids (CNAs) with a polythioether backbone containing repeat units of six atoms, matching the spacing of the phosphodiester backbone of natural DNA. A simple, inexpensive, and scalable route was utilized to produce CNA monomers in gram-scale, which indicates the potential to dramatically lower the cost of these DNA mimics and thereby expand the scope of these materials. The efficiency of this approach was demonstrated by the completion of CNA polymerization in 30 seconds, as characterized by size-exclusive chromatography (SEC) and infrared (IR) spectroscopy. CNA/DNA hybridization was demonstrated by gel electrophoresis and used in CdS nanoparticle assembly.

Synthetic unilamellar liposomes, functionalized to enable novel characteristics and behavior, are of great utility to fields such as drug delivery and artificial cell membranes. However, the generation of these liposomes is frequently highly labor-intensive and time consuming whereas in situ liposome formation presents a potential solution to this problem. A novel method for in situ lipid formation is developed here through the covalent addition of a thiol-functionalized lysolipid to an acrylate-functionalized tail via the thiol-Michael addition reaction with potential for inclusion of additional functionality via the tail. Dilute, stoichiometric mixtures of a thiol lysolipid and an acrylate tail reacted in an aqueous media at ambient conditions for 48 hours reached nearly 90% conversion, forming the desired thioether-containing phospholipid product. These lipids assemble into a high density of liposomes with sizes ranging from 20 nm to several microns in diameter and include various structures ranging from spheres to tubular vesicles with structure and lamellarity dependent upon the catalyst concentration used. To demonstrate lipid functionalization, an acrylate tail possessing a terminal alkyne was coupled into the lipid structure. These functionalized liposomes enable photo-induced polymerization of the terminal alkyne upon irradiation.

An artificial nucleolipid containing thymine, a triazole-ring, and phosphatidylcholine (TTPC) moieties was prepared by copper catalyzed azide alkyne cycloaddition (CuAAC) under aqueous conditions. The resulting TTPC molecules assembled in situ into a fibrous aggregation. The study of the TTPC fiber assembly using XRD and NMR spectroscopy revealed that the formation of fibers was driven by the unique combination of the lipid and nucleobase moieties in the structure of TTPC. At a critical TTPC concentration, entanglement of the fibers resulted in the formation of a supramolecular hydrogel. Investigation of the lyotropic mesophases in the TTPC supramolecular hydrogel showed the presence of multiple phases including two liquid crystal phases (i.e., nematic and lamellar), which have a certain degree of structural order and are promising templates for constructing functional biomaterials.

Thiol lysolipids undergo thiol–thioester exchange with two phenyl thioester-functionalized tails to produce phospholipid structures that assemble into liposomes with differences in exchange rates, temperature sensitivity, permeability, and continued exchange behavior. This in situ formation reaction imparts dynamic characteristics into the membrane for downstream liposome functionalization and mimics native membrane remodeling.

The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin–filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC-active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol-ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m(−3)) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin-based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin–filler interface.

Ductile, cross-linked films were folded as a means to program temporary shapes without the need for complex heating cycles or specialized equipment. Certain cross-linked polymer networks, formed here with the thiol-isocyanate reaction, possessed the ability to be pseudoplastically deformed below the glass transition, and the original shape was recovered during heating through the glass transition. To circumvent the large forces required to plastically deform a glassy polymer network, we have utilized folding, which localizes the deformation in small creases, and achieved large dimensional changes with simple programming procedures. In addition to dimension changes, three-dimensional objects such as swans and airplanes were developed to demonstrate applying origami principles to shape memory. We explored the fundamental mechanical properties that are required to fold polymer sheets and observed that a yield point that does not correspond to catastrophic failure is required. Unfolding occurred during heating through the glass transition, indicating the vitrification of the network that maintained the temporary, folded shape. Folding was demonstrated as a powerful tool to simply and effectively program ductile shape-memory polymers without the need for thermal cycling.

We explain and generalise row and column removal phenomena for Schur algebras via integral isomorphisms between subquotients of these algebras. In particular, we prove new reduction formulae for p-Kostka numbers.

Bulk photopolymerization of a library of synthesized multifunctional azides and alkynes was carried out toward developing structure–property relationships for CuAAC-based polymer networks. Multifunctional azides and alkynes were formulated with a copper catalyst and a photoinitiator, cured, and analyzed for their mechanical properties. Material properties such as the glass transition temperatures (Tg) show a strong dependence on monomer structure with Tg values ranging from 41 to 90 °C for the series of CuAAC monomers synthesized in this study. Compared to the triazoles, analogous thioether-based polymer networks exhibit a 45–49 °C lower Tg whereas analogous monomers composed of ethers in place of carbamates exhibit a 40 °C lower Tg. Here, the formation of the triazole moiety during the polymerization represents a critical component in dictating the material properties of the ultimate polymer network where material properties such as the rubbery modulus, cross-link density, and Tg all exhibit strong depen...

An efficient visible-light-sensitive photobase generator for thiol-Michael addition reactions was synthesized and evaluated. This highly reactive catalyst was designed by protecting a strong base (tetramethyl guanidine, TMG) with a visible-light-responsive group which was a coumarin derivative. The coumarin-coupled TMG was shown to exhibit extraordinary catalytic activity toward initiation of the thiol-Michael reaction, including thiol-Michael addition-based polymerization, upon visible-light irradiation, leading to a stoichiometric reaction of both thiol and vinyl functional groups. Owing to its features, this visible-light photobase generator enables homogeneous network formation in thiol-Michael polymerizations and also has the potential to be exploited in other visible-light-induced, base-catalyzed thiol-click processes such as thiol-isocynate and thiol-epoxy network-forming reactions.

In conjunction with a tertiary amine coinitiator, eosin, a photoreducible dye, has been shown to successfully circumvent oxygen inhibition in radical photopolymerization reactions. However, the role of O2 in the initiation and polymerization processes remains inconclusive. Here, we employ a UV-Vis/FT-NIR analytical tool for real-time, simultaneous monitoring of chromophore and monomer reactive group concentrations to investigate the eosin-activated photopolymerization of PEGDA-based hydrogels under ambient conditions. First, we address the challenges associated with spectroscopic monitoring of the polymerization of hydrogels using UV-Vis and FT-NIR, proposing metrics for quantifying the extent of signal loss from reflection and scattering, and showing their relation to microgelation and network formation. Second, having established a method for extracting kinetic information by eliminating the effects of changing refractive index and scattering, the coupled UV-Vis/FT-NIR system is applied to the study of eosin-activated photopolymerization of PEGDA in the presence of O2. Analysis of the inhibition time, rate of polymerization, and rate of eosin consumption under ambient and purged conditions indicates that regeneration of eosin in the presence of oxygen and consumption of oxygen occur via a nonchain process. This suggests that the uniquely high O2 resilience is due to alternative processes such as energy transfer from photo-activated eosin to oxygen. Uncovering the intricacies of the role of O2 in eosin-mediated initiation aids the design of O2 resistant free radical polymerization systems relevant to photonics, optoelectronics, biomaterials, and biosensing.

We report a dispersion polymerization method based on thiol–Michael addition reactions for the preparation of cross-linked, narrow dispersity microparticles with well-defined, tunable physicochemical properties. Polymerization between pentaerythritol tetra(3-mercaptopropionate) (PETMP) and trimethylolpropane triacrylate in methanol was chosen as a model system, with the addition of triethylamine as a catalyst and polyvinylpyrrolidone as a stabilizer. The formation of microparticles took place within seconds at ambient conditions, as a result of a polymerization driven phase transition from dissolved monomers to precipitated polymers. The particle size was found to be affected by the amount of catalyst, the monomer concentration, and the monomer/polymer solubility in the reaction media. Monodispersity was achieved within a range of particle diameters from 1.6 to 4.3 μm, as determined both by scanning electron microscopy and dynamic light scattering. The reaction kinetics were studied by Fourier transform i...

Objectives To assess the performance of thiol–ene dental composites based on selected ester-free thiol–ene formulations. Further, to point out the benefits/drawback of having a hydrolytically stable thiol–ene matrix within a glass filled composite. Methods Composite samples containing 50–65 wt% of functionalized glass microparticles were prepared and photopolymerized in the presence of a suitable visible light photoinitiator. Shrinkage stress measurements were conducted as a function of the irradiation time. Degrees of conversion were measured by FT-IR analysis by comparing the double bond signals before and after photopolymerization. Mechanical tests were carried out on specimens after curing as well as after extended aging in water. Dynamic mechanical analysis was employed to track the changes in storage modulus near body temperature. The properties of the thiol–ene composites were compared with those of the BisGMA/TEGDMA control. Results Depending on the resin type, similar or higher conversions were achieved in thiol–ene composites when compared to the dimethacrylate controls. At comparable conversions, lower shrinkage stress values were achieved. Although exhibiting lower initial elastic moduli, the thiol–ene composites’ flexural strengths were found to be comparable with the controls. Contrary to the control, the mechanical properties of the ester-free thiol–ene composites were shown to be unaffected by extensive aging in water and at least equaled that of the control after aging in water for just five weeks. Significance Employing non-degradable step-growth networks as organic matrices in dental composites will provide structurally uniform, tough materials with extended service time.

We couple UV–vis and FT–NIR spectroscopy for the real-time monitoring of polymerization reactions, allowing the simultaneous tracking of the rates of light absorption and initiator/monomer consumption, from which dynamic and previously difficult-to-measure parameters are calculated: quantum yields of initiator consumption, initiation and polymerization, photosensitivity, and residual content of leachable chromophore. Estimating these parameters from one set of experiments is not possible with any other probing technique. We demonstrate the potential of this technique using the free radical initiating system including camphorquinone as photoreducible chromophore and amines as reductants for the visible-light-triggered bulk polymerization of methacrylate monomers, important for dental and biomaterials. Photoinitiation by camphorquinone/amine pairs in two dimethacrylates serves to show the importance of obtaining quantum yields in the polymerizing medium instead of using inert solvents. Additionally, the oft...

In this paper we describe the blocks of the partition algebra over a field of positive characteristic.

Liquid crystalline elastomers programmed with light-activated bond exchange allowing controlled shape change., Liquid crystalline (LC) elastomers (LCEs) enable large-scale reversible shape changes in polymeric materials; however, they require intensive, irreversible programming approaches in order to facilitate controllable actuation. We have implemented photoinduced dynamic covalent chemistry (DCC) that chemically anneals the LCE toward an applied equilibrium only when and where the light-activated DCC is on. By using light as the stimulus that enables programming, the dynamic bond exchange is orthogonal to LC phase behavior, enabling the LCE to be annealed in any LC phase or in the isotropic phase with various manifestations of this capability explored here. In a photopolymerizable LCE network, we report the synthesis, characterization, and exploitation of readily shape-programmable DCC-functional LCEs to create predictable, complex, and fully reversible shape changes, thus enabling the literal square peg to fit into a round hole.

Holographic photopolymers capable of high refractive index modulations (Δn) on the order of 10-2 are integral for the fabrication of functional holographic optical elements (HOEs) for use in a range of optical applications. A novel high refractive index liquid writing monomer suitable for two-stage photopolymer systems was designed and synthesized. This monomer exhibits facile synthetic procedure, low viscosity, high refractive index as well as excellent solubility in a low refractive index urethane matrix. The solubility limit, refractive index change and reaction kinetics/conversion were studied against a commercial reference high refractive index monomer, 2,4,6-tribromophenyl acrylate (TBPA). Superior performance in solubility to TBPA is shown with similar reaction kinetics and final conversion as confirmed by realtime Fourier transform infrared spectroscopy (FTIR) and real-time monitoring of diffraction grating growth. We demonstrate the ability to load substantial amounts of these writing monomers enabling a straightforward path to higher achievable Δn values (peak-to-mean Δn ~ 0.03) without sacrificing optical properties (transparency, color or scatter) as validated through recording ~100% efficiency volume transmission holograms in sub-15 μm thick films.

Step-growth thiol-Michael photopolymerizable resins, constituting an alternative chemistry to the current methacrylate-based chain-growth polymerizations, were developed and evaluated for use as dental restorative materials. The beneficial features inherent to anion-mediated thiol-Michael polymerizations were explored, such as rapid photocuring, low stress generation, ester content tunability, and improved mechanical performance in a moist environment. An ester-free tetrafunctional thiol and a ultraviolet-sensitive photobase generator were implemented to facilitate thiol-Michael photopolymerization. Thiol-Michael resins of varied ester content were fabricated under suitable light activation. Polymerization kinetics and shrinkage stress were determined with Fourier-transform infrared spectroscopy coupled with tensometery measurements. Thermomechanical properties of new materials were evaluated by dynamic mechanical analysis and in 3-point bending stress-strain experiments. Photopolymerization kinetics, polymerization shrinkage stress, glass transition temperature, flexural modulus, flexural toughness, and water sorption/solubility were compared between different thiol-Michael systems and the BisGMA/TEGDMA control. Furthermore, the mechanical performance of 2 thiol-Michael composites and a control composite were compared before and after extensive conditioning in water. All photobase-catalyzed thiol-Michael polymerization matrices achieved >90% conversion with a dramatic reduction in shrinkage stress as compared with the unfilled dimethacrylate control. One prototype of ester-free thiol-Michael formulations had significantly better water uptake properties than the BisGMA/TEGDMA control system. Although exhibiting relatively lower Young's modulus and glass transition temperatures, highly uniform thiol-Michael materials achieved much higher toughness than the BisGMA/TEGDMA control. Moreover, low-ester thiol-Michael composite systems show stable mechanical performance even after extensive water treatment. Although further resin/curing methodology optimization is required, the photopolymerized thiol-Michael prototype resins can now be recognized as promising candidates for implementation in composite dental restorative materials.

Adaptable liquid crystal elastomers (LCEs) have recently emerged to provide a new and robust method to program monodomain LCE samples. When a constant stress is applied with active bond exchange reactions (BERs), polymer chains and mesogens gradually align in the strain direction. Mesogen alignment is maintained after removing the BER stimulus (e.g. by lowering the temperature) and the programmed LCE samples exhibit free-standing two-way shape switching behavior. Here, a new adaptable main-chain LCE system was developed with thermally induced transesterification BERs. The network combines the conventional properties of LCEs, such as an isotropic phase transition and soft elasticity, with the dynamic features of adaptable network polymers, which are malleable to stress relaxation due to the BERs. Polarized Fourier transform infrared measurements confirmed the alignment of polymer chains and mesogens after strain-induced programming. The influence of the creep stress, temperature, and time on the strain amplitude of two-way shape switching was examined. The LCE network demonstrates an innovative feature of reprogrammability, where the reversible shape-switching memory of programmed LCEs is readily deleted by free-standing heating as random BERs disrupt the mesogen alignment, so LCEs are reprogrammed after returning to the polydomain state. Due to the dynamic nature of the LCE network, it also exhibits a surface welding effect and can be fully dissolved in the organic solvent, which might be utilized for green and sustainable recycling of LCEs.

Photocleavable liposomes were formed

This study introduces an unexplored method to synthesize and program liquid-crystalline elastomers (LCEs) based on a two-stage thiol–acrylate Michael addition and photopolymerization (TAMAP) reaction. This methodology can be used to program permanently-aligned monodomain samples capable of “hands-free” shape switching as well as offer spatio-temporal control over liquid-crystalline behaviour. LCE networks were shown to have a cytocompatible response at both stages of the reaction.

Light activated polymers (LAPs) have attracted increasing attention since these materials change their shape and/or behavior in response to light exposure, which serves as an instant, remote and precisely controllable stimulus that enables non-contact control of the material shape and behavior through simple variation in light intensity, wavelength and spatially controlled exposure. These features distinguish LAPs from other active polymers triggered by other stimuli such as heat, electrical field or humidity. Previous examples have resulted in demonstrations in applications such as surface patterning, photo-induced shape memory behavior, and photo-origami. However, in many of these applications, an undesirable limitation has been the requirement to apply and maintain an external load during light irradiation. In this paper, a laminated structure is introduced to provide a pre-programmed stress field, which is then used for photo-induced deformation. This laminated structure is fabricated by bonding a stretched elastomer (NOA65) sheet between two LAP layers. Releasing the elastomer causes contraction and introduces a compressive stress in the LAPs, which are relaxed optically to trigger the desired deformation. A theoretical model is developed to quantitatively examine the laminated composite system, allowing exploration of the design space and optimum design of the laminate.

Holographic photopolymers capable of high refractive index modulation (Δn) on the order of 10-2 are integral for the fabrication of functional holographic optical elements that are useful in a myriad of optical applications. In particular, to address the deficiency of suitable high refractive index writing monomers for use in two-stage holographic formulations, here we report a novel high refractive index writing monomer, 1,3-bis(phenylthio)-2-propyl acrylate (BPTPA), simultaneously possessing enhanced solubility in a low refractive index (n = 1.47) urethane matrix. When examined in comparison to a widely used high refractive index monomer, 2,4,6-tribromophenyl acrylate, BPTPA exhibited superior solubility in a stage 1 urethane matrix of approximately 50% with a 20% higher refractive index increase per unit amount of the writing monomer for stage 2 polymerizations. Formulations with 60 wt % loading of BPTPA exhibit a peak-to-mean holographic Δn ≈ 0.029 without obvious deficiencies in transparency, color, or scatter. To the best of our knowledge, this value is the highest reported in the peer-reviewed literature for a transmission hologram. The capabilities and versatility of BPTPA-based formulations are demonstrated at varying length scales via demonstrative refractive index gradient structure examples including direct laser write, projection mask lithography of a 1″ diameter Fresnel lens, and ∼100% diffraction efficiency volume transmission holograms with a 1 μm fringe spacing in 11 μm thick samples.

Synthetic biomacromolecules that mimic natural polymeric structures are of significant interest. For most applications of these materials, however, aqueous solubility is a necessity. Here, we present the synthesis of an intrinsically water soluble single stranded DNA analog formed by the synthesis of a Clickable Nucleic Acid (CNA). These molecules are formed with pendant hydroxyl groups present on the main polymer backbone, and subsequent modification of those hydroxyls with sulfonate moieties further enhances the hydrophilicity of these molecules.