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The current application of renewable resources in vat photopolymerization (VP) 3D printing is rather limited, emphasizing the importance of incorporating bio-based materials into additive manufacturing (AM). In this study, VP 3D printing technology was applied to create composites (derived from soybean oil-based resin) reinforced with cellulose nanocrystals (CNC). Two distinct modifications for CNC, i.e., the acrylation and functionalization with methyl methacrylate, were selected to achieve strong bonding with the UV-curable acrylate matrix. With the use of 0.1 wt% of modified CNC, the resins retain remarkable performance and support the creation of high-resolution prints. The successful integration of modified CNC showed significant improvements in tensile and flexural properties, e.g., elongation at break increased by 75 % and 295 %, respectively. The addition of modified CNC fillers also increased tensile strength by 147 % and flexural strength by 121 %. Fourier-transformation infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) testified to the enhanced interface between filler and matrix. The morphological features and print quality were examined with microscopic analysis, UV-VIS spectroscopy, and colorimetry. The resin showed exceptional printing resolution, characteristic of VP printing, and yielded double bond conversion rates greater than 70 %. The findings presented here indicate that the addition of 0.1 wt% of modified CNC to bio-based resins results in an exceptional increase in the mechanical performance and dimensional stability of printed materials. [Display omitted] • Bio-based UV-curing resin with modified CNC for vat photopolymerization. • The composites retain high optical transparency and 3D printing resolution. • The addition of CNC yielded significant improvements in mechanical properties. • In-depth analysis and characterization of the interface interactions are presented. [ABSTRACT FROM AUTHOR]

Membranes have been extensively investigated as key enabling technologies to exit energy-intensive separation processes. Nevertheless, conventional membrane fabrication techniques present several challenges, such as requiring tight process controls during fabrication to achieve optimal microstructures, geometric limitations, and time-consuming fabrication processes for composite and mixed matrix membranes. Light-induced additive manufacturing (LIAM) has demonstrated potential in the fabrication of complex objects with suitable resolution, accuracy, contactless fabrication and in many cases speed, providing a route to address the aforementioned challenges. Here, we present a review of LIAM in membrane technology, evaluate the fundamental parameters that should be considered when employing LIAM for membrane fabrication, and reflect upon the challenges, opportunities, and future applications of LIAM within the membrane field. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of materials that allow the sustained release of therapeutic proteins is the key feature for improving their pharmacokinetics, bioavailability, and dose reduction. In this context, hydrogels are attracting interest, but their design to provide a sustained release profile is still a challenge. Usually, a large mass of polymer is required to prolong the release of the therapeutic agent, involving hydrogels with high thicknesses, which limits their use in some applications. Here, the synthesis of thin thermoresponsive and functionalized hydrogels (tHGs) for sustained protein release is reported to tackle this problem. tHGs were obtained by photo-crosslinking of linear thermoresponsive polyurethanes (PU) based on polyethilenglycol and a functional diol (methyldiethanolamine) that contribute to tertiary amine functionality. These biocompatible tHGs conserved the thermosensitive property of PU, exhibiting a reversible volume change between the swollen and the collapsed state, as a function of temperature. tHGs were able to load the model protein ovalbumin homogenously in their matrix, and sustainably release it during 25 days with a tuneable profile, by changing the PU composition. Finally, this proposal, which combined a very thin delivery film with a sustained protein release, could be a good candidate for its application in ocular therapy. [Display omitted] • Thin hydrogels through photo-crosslinking of linear thermoresponsive polyurethanes. • Low thickness plataform with long-time sustained release. • Network mesh size and protein-polyurethane interaction control the sustained release. [ABSTRACT FROM AUTHOR]

A novel metal-free photochemical method for the synthesis of porous conjugated polymers was used to investigate the effects of introducing thiophene co-monomer to the carbazole-based polymer, 4,4′-bis(3,6-di(thiophen-2-yl)-9H-carbazol-9-yl)-1,1′-biphenyl (CBP–Th), in terms of its structural, optical, electrochemical and morphological properties. Irradiation of a CBP-Th monomer solution led to the formation of a dark-colored polymer, PCBP-Th, and the role of thiophene on polymerization was investigated, involving electron transfer between CBP-Th and the iodonium ion in the exciplex produced by proton release and radical coupling reactions. The UV–Vis spectra broadened and redshifted due to the elongation of conjugation and solid-state π-π interactions by extra thiophene additive after the polymerization process. The addition of thiophene co-monomer also resulted in decreasing the onset potentials and thus slightly raised HOMO positions determined by the DPV technique. In theoretical calculations, it has been observed that the charge distribution of PCBP-Th at HOMO is over the entire conjugated structure and it has localization in thiophene-thiophene bridges at LUMO. Since the thiophene co-monomer changes the intermolecular distance, the thermal stability of PCBP-Th polymers decreases and accordingly increases the amorphous characters. According to AFM, TEM and SEM images, introducing the thiophene co-monomer led to the formation of larger clusters, resulting in a more pronounced surface texture on both the powders and thin films. [Display omitted] • Environmental approach for covalent organic polymer synthesis by incorporating thiophene units into carbazole-based polymers. • Thiophene content affects polymer properties, including electrochemical charge distribution, and thermal stability. • Synthesizing polymers with controlled porosity for various electronics and energy conversion applications. [ABSTRACT FROM AUTHOR]

This work is aimed to fabricate ultra-thin coatable polarizers on a single substrate based on "host-guest" effect between highly ordered smectic reactive mesogen (RM) and dichroic dye. We designed and synthesized a new tolane-based RM with a highly ordered smectic A phase at room temperature. Polymerizable "host-guest" mixture was formulated from the host RM, dichroic dye and additives, then spin-coated on a single substrate having an alignment layer. Subsequent in-situ photopolymerization by UV irradiation successfully resulted in a coatable polarizer with good polarizing properties. The fabricated coatable polarizer showed a dichroic ratio (DR) of 16.4 and a degree of polarization (DOP) of 99.3% with the thickness of 4 μm. The resulting coatable polarizer possessed a considerable solvent resistance, good thermal stability and robust mechanical properties. Moreover, we prepared a TN-mode LC cell by using the prepared coatable polarizers inside the cell (in-cell), in which the coatable polarizers acted as a polarizer and an alignment layer, simultaneously. The resulting TN cell with in-cell polarizers exhibited a decent electro-optical behavior. We believe that the coatable polarizer proposed in this study possesses practical application potential in ultra-thin LCDs or flexible OLEDs. Image 1 • Reactive mesogen with smectic A phase was synthesized for coatable polarizer. • Coatable polarizer was fabricated on a single substrate by "host-guest" method. • Coatable polarizer exhibits considerable optical property and excellent stability. • LCD with in-cell structure was demonstrated by using the prepared coatable polarizer. [ABSTRACT FROM AUTHOR]

A novel approach to fabricate epoxy-based polymer-stabilized liquid crystals (EPSLCs) via the cationic photopolymerization of liquid crystalline epoxide in mesogenic solvents was presented. The photoinitiated cationic polymerization of liquid crystalline epoxide in different mesogenic solvents was compared and the liquid crystalline epoxy polymer (LCEP) network can only be formed in the particular solvents. The different photo-curing behaviors of the liquid crystalline epoxide in various solvents may be ascribed to the solvent effect and the content of the nucleophilic groups had a decisive influence on the formation of the LCEP network. The epoxy polymer/liquid crystal (LC) composites were also prepared by the cationic photopolymerization of different epoxy monomers in LC solvent. The morphology of the epoxy polymers in the composites and the change of the arrangement of LC molecules before and after polymerization were also studied. Moreover, the stabilizing effect of the LCEP network on the LC molecules was also characterized by the electric-optical performance test. This report can offer an innovative technique to fabricate EPSLCs and provide a promising means for the development of functional epoxy polymer composites. Image 1 • The cationic photopolymerization of liquid crystalline epoxide in different mesogenic solvents was investigated. • A novel approach to fabricate epoxy-based polymer-stabilized liquid crystals via cationic photopolymerization was reported. • The morphology of the epoxy polymers and the change of the arrangement of LC molecules after polymerization were studied. • The stabilizing effect of the LCEP network on the LC molecules was characterized by electric-optical test. [ABSTRACT FROM AUTHOR]

Abstract Atom transfer radical polymerization (ATRP) performed in ab initio emulsion provides access to well-defined polymers in a low-cost, eco-friendly environment. Herein, photoinduced ab initio emulsion ATRP of various (meth)acrylate monomers is reported. The polymerization rate increased with the solubility of the monomer in water. Well-controlled (co)polymerizations were achieved under violet light and low catalyst loading, even in an open-to-air system through enzymatic degassing. Graphical abstract Image 1 Highlights • PhotoATRP conducted in ab initio emulsion. • Rate of polymerization correlated to monomer hydrophobicity. • Enzymatic deoxygenation enabled simplified reaction setup at low cost. • Highly hydrophobic monomers shuttled by more hydrophilic monomers to form copolymers. • Facile copolymers preparation by feeding the second monomer in situ [ABSTRACT FROM AUTHOR]

Abstract Well-defined poly(methyl acrylate) (PMA) and poly(n -butyl acrylate) (PBA) are prepared via photochemically induced atom transfer radical polymerization (photoATRP) using ppm amounts of CuBr 2 /tris[2-(dimethylamino)ethyl]amine (Me 6 TREN) catalyst complex without degassing of the polymerization mixture. The effect of light intensity and partial replacement of the excess of expensive Me 6 TREN ligand with cheaper tertiary amines on kinetics of the polymerization was investigated in various solvents. The addition of triethylamine to photoATRP system resulted in both significant shortening the induction period and increasing the polymerization rate. High livingness of the oxygen tolerant photoATRP system containing triethylamine was proved by chain-extension polymerizations resulting in formation of PMA- b -PBA copolymer. The presented photoATRP system can have tremendous importance from an industrial point of view since the well-defined polyacrylates can be prepared almost without any induction period and in short polymerization time without necessity of both air removal and using the excess of expensive ligand. Graphical abstract Image 1 Highlights • Addition of aliphatic tertiary amines can shorten the induction period. • Addition of triethylamine increases the polymerization rate. • Increased light intensity increases the polymerization kinetics. [ABSTRACT FROM AUTHOR]

Abstract In order to improve epoxide kinetic outcomes and to control the phase separation that can occur in cationic/free-radical hybrid systems, the cationic activated monomer (AM) mechanism was promoted through a hydroxyl functional group on the (meth)acrylate, covalently bonding (meth)acrylate chains and epoxide networks. The impact of the AM mechanism on the reaction kinetics and physical properties was studied using real-time Raman spectroscopy and dynamic mechanical analysis to compare a hydroxyl-containing acrylate and methacrylate to non-hydroxyl-containing controls. The promotion of the AM mechanism improved epoxide conversion and polymerization rate. The effect on the (meth)acrylate kinetics correlated to the propagation rate of the neat (meth)acrylate. Formulation viscosity did not have a significant impact in these hybrid systems. The presence of the hydroxyl group increased network homogeneity and cross-link density, yet still allowed control of the glass transition temperature in the hybrid systems by varying the ratio of epoxide to (meth)acrylate. Graphical abstract Image 1 Highlights • Promotion of the AM mechanism improved epoxide conversion and polymerization rate. • Hydroxyl groups increased network homogeneity and cross-link density. • Formulation viscosity did not have a significant impact in these hybrid systems. • T g trends were not affected by the presence of the hydroxyl groups. • Monomer selection and ratio enable kinetic and property control of hybrid systems. [ABSTRACT FROM AUTHOR]

Abstract In this work, the inhibition and termination reactions occurring throughout a free radical photopolymerization initiated by a type-I photoinitiator are studied by kinetic modeling. The role of the macroradicals as the main oxygen trapping agents during the inhibition time is identified, and the absence of primary radical consumption by oxygen can be related to a high initiation efficiency at early times. The ratio of the termination reactions reveals that bimolecular termination remains the principal pathway for the cessation of macromolecule growth, even at high polymer conversion. Moreover, the evolution of the termination ratio during the polymerization can be correlated to both the diffusional control of the polymerization reactions as the polymer network grows and the photoinitiator consumption. Finally, the effect of the incident light intensity and the initial photoinitiator concentration on the termination reactions is assessed, and the validity of the steady-state assumption applied to the macroradical concentration discussed. Graphical abstract Image 1 Highlights • Kinetic modeling is useful to study inhibition and termination reactions. • Macroradicals are the principal oxygen trapping agents throughout the inhibition. • The ratio of the termination pathways evolves during the photopolymerization reaction. • Bimolecular termination is the main termination reaction all along the process. • Incident intensity and photoinitiator concentration affect the termination ratio. [ABSTRACT FROM AUTHOR]

Abstract A new class of ionogels with a thiol-ene matrix showing a phase-separated morphology was obtained from triallyl isocyanurate and trimethylolpropane tris(3-mercaptopropionate) via a photo-induced polymerization in ionic liquids (ILs). The compatibility between the polymer matrix and ILs decreased with the decrease of the Kamlet-Taft α parameter of the solvent; polymerization was faster in ILs with higher values of the Kamlet-Taft β parameter. The matrix had a "colloidal gel" structure built of interconnected microspheres forming a 3-dimensional network percolating throughout the IL. For the first time, spherical poly(thiol-ene) particles were obtained in ILs; the size of the particles depended on the monomer concentration and the IL ability to stabilize the colloidal microspheres through H bonding. The low solubility of ILs in the matrix along with sufficiently strong interactions matrix/IL resulted in the appearance of anti-plasticization effect. The obtained ionogels had high ionic conductivity (∼2.6 ÷ ∼ 7.0 mS cm−1 at 25 °C) and very high relative conductivity (higher than the highest possible values resulting from the IL content); this allows the majority of the IL conductivity in the ionogel to be retained. Graphical abstract Image 1 Highlights • Ionogels with thiol-ene matrix, prepared by photopolymerization in ionic liquids. • Phase-separated morphology of the ionogels produced. • First report on the formation of thiol-ene polymer microspheres in ionic liquids. • Anti-plasticizing effect of ionic liquids on the thiole-ene matrix. • High ionic conductivity of the ionogels produced. [ABSTRACT FROM AUTHOR]

Abstract Dimanganese decacarbonyl (Mn 2 (CO) 10) and alkyl halide combination has unique visible light radical generating property which is useful in the fabrication of many complex macromolecular structures. Herein, we present a generic simple and rapid synthetic approach for the preparation amphiphilic hyperbranched macromolecular structures with controlled branching density and hydrophilicity. The method is based on the visible light induced self-condensing vinyl copolymerization of methyl methacrylate (MMA), 2-(2-bromoisobutryloxy)ethyl methacrylate (BIBEM) and poly(ethylene glycol) methyl ether methacrylate as monomer, inimer and hydrophilic comonomer, respectively, in the presence of Mn 2 (CO) 10. The resulting polymers possess both hydrophobic and hydrophilic sequences offering many potential bio applications such as controlled drug delivery and release. Moreover, the resulting polymers contain also unreacted bromide groups in the final structure which allow postfunctionalization through copper(I)-catalyzed alkyne-azide cycloaddition "click" reactions. Graphical abstract Image Highlights • A simple and rapid photopolymerization route for the synthesis of hyperbranched amphiphilic copolymers. • One pot, one step, mild and green conditions. • Controlled branching density and hydrophilicity. [ABSTRACT FROM AUTHOR]

Abstract Photo-induced polymerization by nanomaterials and their analyses are challenging topics with combines multiple fields of research. The first one, the preparation/characterization of surface modified ZnO nanoparticles is by far the most obvious one. Photosensitive semiconductors can lead to a replacement of migrating initiators by non-migrating nanoscaled photo-initiators (NanoPI) for radical polymerization. The class of NanoPI is especially promising to be applicable in printing/coating applications to result in organic inorganic hybrid materials and to reduce health risks by reducing/preventing contamination of the surroundings by gas-phase transfer, by diffusion of reacted/remaining compounds (migration) and so on. The polymer related area of the research (analysis of the kinetic) is the main part of the discussion within this contribution. The reactivity of the particles to initiate free-radical polymerization of bulk printable resin mixtures (the performance of the curing) is proven for LED@365 nm and simulated LED illumination. Finally, the novel kinetic analysis method, the transmission UV-vis solidification is explained in detail within the present manuscript. Graphical abstract Image 1 Highlights • ZnO particle-based initiation system: Synthesis and Radical polymerization. • Photo-Kolbe reaction. • Real time LED@365 FT-IR and simulated LED@365. • Systematic kinetic analysis using a novel transition UV-vis solidification. • Transition UV-vis measurements and benzoyl formic acid/NaOH content variation. [ABSTRACT FROM AUTHOR]

Flexible ionic conductors with excellent mechanical properties, stability and conductivity from green and efficient fabrication technology have great application potentials in the intelligent devices. In this work, we reported an ionic conductor fabricated from the polymerization of the polymerizable deep eutectic solvent (PDES) reinforced by the hydroxyethyl cellulose (HEC). The PDES with the cationic hydrogen bond acceptor as the polymerizable unit was synthesized from the methacrylate of the 2-choline bromide (ChBrMA) as hydrogen bond acceptor and the glycerol (Gly) as hydrogen bond donor. The PDES has solubility to dissolve the HEC and thus the HEC-reinforced poly (PDES) ionic conductors were successfully prepared by one step photopolymerization. The addition of HEC enhanced the mechanical strength of poly (PDES)-based ionic conductor. The ionic conductors present the characteristics of good elasticity, puncture resistance, heat resistance and low volatility, and their electrical conductivity reached 2 × 10−2 S/m at room temperature. Finally we assembled a flexible sensor which can accurately detect the movement of human fingers and monitor the change of environmental temperature in real time, demonstrating their potentials in the multifunctional sensors with long-term durability. [Display omitted] • A polymerizable deep eutectic solvent (PDES) was synthesized. • HEC-reinforced poly (PDES) ionic conductors were prepared by photopolymerization. • Ionic conductors present high elasticity and electrical conductivity ∼ 2 × 10−2 S/m. • Flexible conductor can be used as multifunctional sensors with long-term durability. [ABSTRACT FROM AUTHOR]

Abstract Here, a process is introduced for forming dual stage thiol-Michael/acrylate hybrid networks photocured by two different wavelengths, demonstrating its use in nanoimprint lithography (NIL) and shape memory materials. Initiated with a visible light sensitive photobase and a UV-sensitive radical initiator, thiol-Michael-acrylate hybrid polymerizations were programmed to proceed sequentially and orthogonally, with base-catalyzed thiol-Michael photopolymerization as the first stage and radical mediated acrylate photopolymerization as the second stage. By regulating the photopolymerization formulations, i.e. thiol-to-acrylate ratios, initiator loadings and irradiation conditions, a series of materials with highly tunable mechanical performance was achieved, with ultimate T g values ranging from 23 to 70 °C. With a photopatternable first stage and a readily reconfigurable second stage, its implementation in nanoimprint lithography (NIL) enabled surface features on the scale of 10 nm to be formed on a photopatterned substrate. Additionally, the dual stage polymer results in a relatively homogenous polymer network with a narrow glass transition temperature (Tg), which enables rapid response in applications as shape memory materials, with shape-fixity values above 95% and shape-recovery values above 99%. With its unique photocuring process and programmable mechanical properties, the two color light controlled photopolymerization can be exploited as a useful tool in a wide range of materials science applications. Graphical abstract Image 1 Highlights • A photo-induced multistage polymerization was achieved in the thiol-Michael/acrylate hybrid polymer system. • Nanoscale features (<10 nm) were created on the photopatterned surfaces by this multistage polymerization. • The multistage polymers were used to produce shape memory materials with simple, three-dimensional structures. [ABSTRACT FROM AUTHOR]

Abstract Silk fibroin (SF) hydrogel has been highlighted for its unique physical property as well as biocompatibility. SF hydrogel is easily formed from aqueous solution by physical crosslinking via β-sheet structure formation. However, such a physically formed SF hydrogel is mechanically poor with low reproducibility. Alternatively, SF hydrogel formation can be achieved by chemical cross-linking, which is able to precisely control the network density with high reproducibility. Nevertheless, chemical cross-linking process is very restricted for SF since it is very difficult to maintain homogeneous reaction condition in SF solution. To achieve controlled crosslinking, we synthesized SF-methacrylate (SFMA) with hydrolyzed SF and fabricated SF hydrogel via photo-crosslinking in the presence of photoinitiator. SFMA powder synthesized with 25 kDa SF showed good water-solubility at various degrees of methacrylation as well as quick gelation time (<60 s). In addition, the photo-crosslinked SF hydrogel showed a wide property control range with higher elasticity compared to physically crosslinked SF hydrogel. Graphical abstract Image 1 Highlights • Synthesis silk fibroin-methacrylate with hydrolyzed silk fibroin. • Quick and facile silk fibroin-methacrylate hydrogel formation via photopolymerziation. • Characterization of physical and structural property of silk fibroin-methacrylate hydrogels. [ABSTRACT FROM AUTHOR]

Abstract Phase separation of trimethylolpropanetriacrylate/poly(styrene-co-methylmethacrylate) induced by UV-irradiation (photo-PIPS) has been studied. Three poly(St-co-MMA) with St:MMA monomer ratio of 25:75, 50:50 and 75:25 were synthesized with average molecular weight of Mw ≈ 5 × 104 and average Tg being ≈345 K, due to stereoirregularity in their structure. Difference in TMPTA/poly(St-co-MMA) blends compatibility caused different extents of photo-PIPS and final conversion status depended on the copolymer type and amount. Optical microscopy used to study time-evolution of photo-PIPS. SEM observation showed that, within studied range of copolymer content, droplet domains of copolymer-rich phase appeared in TMPTA-rich matrix through viscoelastic photo-PIPS and in copolymer-rich domains network-like structures of TMPTA were formed. Also some columns were created due to copolymer extrusion to the surface of the sample. Size of the copolymer-rich domains, their formation procedure and size of the columns depended on the copolymer type and amount. SEM Carbon-mapping confirmed copolymer extrusion to the surface. Based on AFM phase-mode images medium-, low- and high-modulus regions were detected and assigned to the TMPTA-rich matrix phase, copolymer-rich phase and TMPTA-rich phase of copolymer-rich domains, respectively. These corresponds to peaks of tan δ curves used to determine mentioned phases composition. Graphical abstract Image 1 Highlights • Use compatibility of thermoplastic/thermoset blends to create special morphologies. • Reduction of crosslinking kinetics to make phase separation reach the desired extent. • Clarification of viscoelastic phase separation in bulk and phase separated domains. • Use of thermoplastics to increase final conversion in photo-polymerized blend. [ABSTRACT FROM AUTHOR]

More recently, three dimensional printing (3D Printing), also known as an additive manufacturing (AM), has been highlighted since it shows a great promise to realize almost any three dimensional parts or structures with computer aided design (CAD). Several different processes are available for 3D printing, which includes fused deposition modeling, selective laser sintering, stereolithography, photopolymerization, and etc. In particular, considerable attention is paid to the 3D printing technique with photopolymerization due to their high resolutions. Unfortunately, the 3D printed products with photopolymerization however possess poor mechanical properties. Understanding of this should be necessary for the advantages of the 3D printing to be fully realized. Here, this study experimentally investigates the mechanical properties of the 3D printed photopolymer through thermomechanical analysis and tensile testing. In this study, it is found that the printed specimens are not fully cured after the 3D printing with photopolymerization. DiBenedetto equation is employed to better understand the relationship between the curing status and tensile properties. In addition to the poor mechanical properties, anisotropic and size dependent tensile properties of the 3D printed photopolymers are also observed. Electron beam treatment is used to ensure the cure of the 3D printed photopolymer and the corresponding tensile properties are characterized and investigated. [ABSTRACT FROM AUTHOR]

In this work, stimuli-responsive, superabsorbent materials are created by copolymerization of stimuli-responsive poly( n -isopropyl acrylamide) (PNIPAM) in combination with superabsorbent sodium acrylate (SA) via photopolymerization in lyotropic liquid crystal (LLC) templates. Templating PNIPAM in LLC mesophases imparts nanostructure to the polymer that significantly increases transport and swelling when compared to isotropic hydrogels. These materials exhibit twice the equilibrium swelling of analogous non-templated materials and show a dynamic range between the swollen and deswollen state that is 5 times greater. To further augment this stimuli-responsive range, LLC-templated PNIPAM was combined with the superabsorbent monomer sodium acrylate (SA). As SA concentration is increased, significant structure changes are observed during polymerization that leads to less-defined nanostructure and lower stimuli response. Maximum swelling and temperature response are observed at low concentrations of SA (∼2 wt%). These LLC-templated copolymers exhibit stimuli-responsive volume transitions up to 40 times and equilibrium swelling ratios of 60 times their dry mass. This 600% increase in thermal response is due to the combined high swelling capabilities of SA with the enhanced thermal-response behavior induced by the LLC-templated nanostructure. Additionally, the nanostructure induces fast deswelling rates at temperatures above the lowest critical solution temperature of PNIPAM. The high dynamic range and quick response of this composition could allow for the development of superabsorbent, stimuli-responsive hydrogels in a variety of biomaterial, microfluidic, and water remediation applications. [ABSTRACT FROM AUTHOR]

The synthesis of polymeric nanocapsules by means of miniemulsion cationic polymerization has been investigated here. The core-shell structure was obtained by confining the reaction at the interface between continuous and dispersed phase of an oil-in-water miniemulsion. This hallmark also allows to carry out the cationic UV-activated polymerization of a vinyl monomer, namely triethylene glycol divinyl ether, in water. The study firstly focused on formulation design. Various kinds of surfactant were examined and SDS provided optimal miniemulsion stability. Moreover, several amounts of surfactant, photoinitiator and oil were tested to optimize formulation composition. Nanocapsules were successfully synthesized and their average size, dimensional distribution, surface zeta potential, stability over time, morphology and thermal behavior were explored. Then, processing conditions, namely irradiation time and sonication time, were investigated. Results highlighted the possibility to design nanocapsule dimension by acting on ultrasound exposure time and a minimum size of 200 nm was identified. [ABSTRACT FROM AUTHOR]

Soft poly(thioether) thermosets have been synthesized by employing a two-step curing procedure based on click chemistry. The first stage of curing is a thiol-Michael addition between acrylates (or methacrylates) and thiols in excess, catalyzed by a set of novel tertiary amine catalyst comonomers with allyl functionality. Subsequently, the pendant allyl groups of the comonomer get incorporated into the polymer network by undergoing thiol-ene UV photopolymerization with the remaining thiols. The strong catalysis by the high concentration of tertiary amine groups facilitates quantitative conversions at the end of the first stage. All remaining functional groups are depleted after a short period of UV irradiation. Final materials are clear, transparent, and exhibit homogeneous network structures with alpha relaxation temperatures in the range 3–25 °C. This sub-ambient relaxation temperature range suggests these materials may be suitable for coating applications where delicate substrates are involved such as plastic, wood and paper. [ABSTRACT FROM AUTHOR]

A two-step wet chemical method is described for the preparation of spherical silver nanoparticle-decorated flower-shaped zinc oxide (ZnO@Ag) heteronanostructures using a newly designed redox-active poly(ionic liquid)(PIL), poly(1-vinyl-3-butylimidazolium ascorbate) (P[VBuIm][As]). The first step is the generation of ZnO nanoflower using P[VBuIm][As] in water followed by its decoration with in situ formed Ag nanoparticles (AgNPs) by the reduction of AgNO 3 with surface adsorbed ascorbate ion. P[VBuIm][As] plays a triple role as shape-directing-cum-capping agent, mediator for Ag + reduction and inducing the formation of spherical AgNPs. The composite ZnO@Ag heteronanostructures are thoroughly characterized by FESEM, TEM and XRD. The as-synthesized ZnO@Ag heteronanostructures is found to be excellent composite photocatalyst towards photopolymerization of methyl methacrylate (MMA) to very high-molecular-weight poly(methyl methacrylate) (PMMA) (Ca. ∼2 × 10 5 ) with very high (82%) conversion in bulk and in solution without any photoinitiator under UV light irradiation ( λ max = 350 nm). The ZnO@Ag composite is also an efficient photocatalyst for styrene polymerization in bulk and N -isopropylacrylamide polymerization in water. The photopolymerization with neat ZnO nanoflower catalyst also produces PMMA, but molecular weights are comparatively low with a low conversion. The ZnO@Ag composite photocatalyst is easily isolable by centrifugation after polymerization, is stable and is reusable for four cycles of polymerization of MMA in bulk condition without losing its original activity. [ABSTRACT FROM AUTHOR]

In this work we develop thermoset materials with heterogeneous microstructures on sub-micron scales by photopolymerization-induced phase separation (photo-PIPS). To this end, we designed a photo-curable resin based on pentaerythritol tetraacrylate (PETA), an acrylate monomer, combined with 2-ethylhexyl methacrylate (2-EHMA), a methacrylate diluent. Polypropylene glycol (PPG) was used as a phase separation agent. Phase separation was monitored by reactive light transmittance using a custom-built light transmission apparatus and through dynamic mechanical analysis (DMA). The photopolymerization kinetics and the microstructure morphology were characterized using real-time Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), respectively. We observe double phase separation: PETA and 2-EHMA separate due to different reactivities, while PPG phase separates as the network develops due to immiscibility. A synergy is observed between the two processes: PPG phase separation leads to an enhanced separation of 2-EHMA. Phase separation leads to reduced transmittance due to scattering, which is primarily associated with the separation of 2-EHMA. Phase separation also causes the reduction of stiffness due to the formation of PPG subdomains. The kinetics is enhanced by increasing the PPG molecular weight and increasing the irradiation intensity. [Display omitted] • Photo-PIPS is studied in a system composed from PETA, 2-EHMA and PPG. • Both 2-EHMA and PPG phase separate. • Separation of 2-EHMA is enhanced as the PPG molecular weight increases. • Reduced transmittance is observed as phases separate. • The material stiffness decreases due to PPG phase separation. [ABSTRACT FROM AUTHOR]

The chemical and mechanical properties of macroporous polymer substrates play a crucial role in the determination of their end-application. The preparation of highly (macro)porous monolithic polymers (polyHIPEs) by emulsion templating and thiol-ene/yne photopolymerisation, using multifunctional acrylate, allyl ether and alkyne-based monomers with trimethylolpropane tris (3-mercaptopropionate) (TMPTMP), is described in this work. Issues associated with monomer solubility and/or stability of the produced high internal phase emulsions (HIPEs) are tackled. Scanning electron microscopy (SEM) is used to study the morphology and porosity (average void diameters) of the obtained materials. Due to the nature of the photoinitiated thiol-ene reactions, materials obtained from acrylate monomers display residual thiols that are quantified by a colourimetric (Ellman's) assay. Raman spectroscopy is also shown to be a complementary technique to evaluate the residual thiol content. The influence of the monomer functionality on the mechanical properties of the material is explored using compression tests. Significant differences in the surface functionality and mechanical behavior between materials prepared with comonomers able to homopolymerise (acrylates) and those unable to homopolymerise (allyl ethers; alkynes) are demonstrated. [ABSTRACT FROM AUTHOR]

A photocrosslinked membrane (M-Cl) based on vinyl-pyrrolidone/butyl acrylate containing ethylene glycol dimethacrylate as a crosslinking agent and methacryloyl chloride as reactive monomer has been prepared for further functionalization. A series of hydroxy substituted piperazine naphthalimide compounds have been synthetized as pH sensitive Off-On fluorescence probes using two methods: microwave and reflux. Three of the derivatives were selected to be anchored to the M-Cl membrane through the acid chloride groups by the Schotten-Baumann reaction. All the obtained water-swollen membranes were characterized using different techniques. Photo-induced electron transfer (PET) and its pH-dependent optical changes were investigated and various photochemical parameters were determined by using pH-dependent absorption and fluorescence spectroscopies. In the pH range of 9.0–4.0, these solid sensors undergo PET process from the piperazine to the naphthalimide moiety leading to a fluorescence quenching. However, in the pH range of 4.0–1.0, the PET is inhibited to give a fluorescence enhancement. The sensitivity of the functionalized membranes to pH changes depended on the size and position of the naphthalimide substituents. [ABSTRACT FROM AUTHOR]

Two new near-UV and visible-light-sensitive photobase generators (PBGs) are synthesized and investigated. They are built on a near-UV and visible light sensitive ( E )-3-(2,2′-bithiophen-5-yl)-2-cyanoacrylic acid chromophore and a latent strong base such as 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD). Upon irradiation, decarboxylation occurs and the base is released. The anionic curing of epoxy/thiol as well as thiol/divinylsulfone formulations in the presence of these PBGs under LEDs at 385 and 405 nm is studied. More than 60% of conversion of the thiol and epoxy functions is achieved upon LED@385 nm without any post baking. [ABSTRACT FROM AUTHOR]

Poloxamer 407 (P407) and poly (ethylene glycol) diacrylate (PEG-DA) are well-characterized building blocks for physical and chemical hydrogels, respectively. P407 physical hydrogels alone can be used as injectable hydrogels, but lack mechanical stability. In this contribution, PEG-DA was added to physically gelling P407 solutions in order to introduce chemical curing ability. The resulting hydrogel formulations containing P407, PEG-DA ( M n = 700 g mol −1 ) and the photoinitiator 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959) were characterized concerning their physical and chemical gelling behavior. Upon addition of PEG-DA to P407 solutions, their gel transition temperature T gel was altered and could be adjusted between 10 °C and 39 °C. At P407 concentrations c Polox of <22.5 wt.-%, T gel increased compared to P407 solutions by adding PEG-DA. At c Polox >22.5 wt.-% T gel decreased. The different behavior at different c Polox could be explained by a combination of a decrease of P407 micelle size as well as a decrease of the critical mizellization temperature of P407 upon PEG-DA addition. Chemical gelation of the formulations was investigated by real-time FT-IR spectroscopy combined with photorheology as well as by the equilibrium degree of swelling and shear moduli of the cured hydrogels. Hydrogel curing was significantly faster without altering the double bond conversion when P407 was present in the formulations, probably due to prearrangement of the double bonds. The shear moduli and equilibrium degrees of swelling of the cured hydrogels could be adjusted by the PEG-DA concentration in the formulation, similar to pure PEG-DA hydrogels. The hydrogel formulations presented are promising candidates for injectable hydrogels with chemical curing ability. [ABSTRACT FROM AUTHOR]

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%. [Display omitted] • Radical ring opening photopolymerization of cyclic allylic sulfides monomers. • Low oxygen sensitivity of the cyclic allylic sulfides monomer photopolymerization. • Lower volume contraction than acrylate monomer with a value of less than 1.5%. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Indeno- and indoloquinoxalines coupled with thiophenoxyacetic acid were used as photoinitiating systems for dental applications. • The systems were able to control the polymerization under 400–500 nm LED irradiation. • The structural alterations of dyes noticeably influence their spectral and photoinitiating properties. • A decrease in temperature during photopolymerization and an increase in polymer hardness were observed. [ABSTRACT FROM AUTHOR]

Deep eutectic ionic elastomers (DEIEs) as emerging iontronic conductors have shown great interest in flexible and wearable electronics. However, developing DEIEs with high strength and extreme stretchability remains challenging. In this paper, we report a facile strategy to prepare superior DEIEs by directly photopolymerizing HEA and ChCl. The synthetic elastomer exhibits high mechanical properties, with fracture strength of 0.804 MPa and fracture strain up to 1814%. Impressively, this elastomer can tolerate cutting and lift as high as 5 kg (7700 times its own weight) without failure. Moreover, the DEIEs also possess outstanding optical transparency (>90% in the visible range), desirable conductivity (2.47 × 10−5 s cm−1), and excellent self-healing ability (electrical healing efficiency of 99.9% within 0.2 s). Using their strain-dependent iontronic resistance properties, versatile iontronic sensors for motion detection could be realized for human health care. [Display omitted] • Deep eutectic ionic elastomers (DEIEs) were prepared by photopolymerizing HEA and ChCl. • The DEIEs exhibit high optical transparency, stretchability and fracture strength. • The electric healing efficiency of DEIEs can reach 99.9%. • The flexible DEIE-based sensor shows strain-dependent resistance properties with linearity. • The obtained sensor could be used to monitor human movement for people health care. [ABSTRACT FROM AUTHOR]

Crosslinked polymeric networks have been utilized as effective building blocks for the development of a variety of multifunctional materials in materials science, nanoscience, and industrial fields. Here, we report thiol-ene polysulfide-crosslinked polymethacrylate networks reinforced with aluminum oxide nanoparticles (ALNPs) prepared by photo-induced thiol-ene radical addition for reactive blends consisting of functional polymethacrylates having pendant vinyl and SH groups with different molecular weights in the presence of ALNPs. Various techniques including viscoelastic measurement, nano-scratch test, differential scanning calorimetry, and thermogravimetric analysis allow for elucidating the effect of ALNPs on the properties of thiol-ene crosslinked films. Analysis of these results, combined with optical and scanning electron microscopy, suggests that the introduction of an optimal amount of ALNPs and the design of relatively low molecular weight polymethacrylates resulted in enhanced scratch resistance and thermal stability of thiol-ene sulfide-crosslinked networks. [ABSTRACT FROM AUTHOR]

Artificial wrinkles have recently been in the spotlight due to their potential use in high-tech applications. A spontaneously wrinkled film can be fabricated from UV-crosslinkable liquid prepolymers. Here, we controlled the wrinkle formation by simply formulating two UV-crosslinkable liquid prepolymers, tetraethylene glycol bis(4-ethenyl-2,3,5,6-tetrafluorophenyl) ether (TEGDSt) and tetraethylene glycol diacrylate (TEGDA). The wrinkles were formed from the TEGDSt/TEGDA formulated prepolymer layers containing up to 30 wt% of TEGDA. The wrinkle formation depended upon the rate of photo-crosslinking reaction of the formulated prepolymers. The first order apparent rate constant, k app , was between ca. 5.7 × 10 −3 and 12.2 × 10 −3 s −1 for the wrinkle formation. The wrinkle structures were modulated within the k app mainly due to variation in the extent of shrinkage of the formulated prepolymer layers with the content of TEGDA. [ABSTRACT FROM AUTHOR]

A series of thiol-ene (1.1:1 equiv) polymer microbeads (PMBs) were prepared via a high-shear suspension photopolymerization method to explore the physical properties of the networks as a function of composition. 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H, 3H, 5H)-trione (TTT) and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) PMBs were selected for the synthesis of a heterogeneous photocatalyst. Particle size was characterized using DLS and OM, and thermal stability and T g were assessed using TGA and DSC. PMBs produced from higher functionality monomers produce smaller particles, and T g increased with monomer rigidity. TTT-PETMP PMBs were derivatized with C 60 to demonstrate the accessibility and reactivity of the residual thiols, successful inclusion of C 60 as the reactive ene moiety, and overall PMB utility as a scaffold material. Upon capping with C 60 , the T g of the composite particles increased significantly. Most importantly, the C 60 -capped PMBs produced singlet oxygen in direct and indirect chemical assays, and the efficiency did not decrease after recycling. [ABSTRACT FROM AUTHOR]

In this study, the key factors for controlling the average fiber diameter and diameter distribution of fibers made via simultaneous centrifugal spinning and UV initiated polymerization are elucidated. Through systematic investigation, it was found that the average fiber diameter has a strong dependence on monomer delivery rate through the orifice, which can be intuitively linked to both the orifice diameter and monomer mixture viscosity. On the other hand, the breadth of the fiber diameter distribution can be controlled by the spin speed of the rotating spinneret. Carefully tuning these process parameters allows near independent control of average fiber diameter and its distribution, which could provide access to a widely tailorable range of fibers appropriate for different applications. Finally, under optimized process conditions, crosslinked fibers with average diameters of approximately 1.5 μm can be produced, which are one to two orders of magnitude smaller than photocured fibers fabricated in previous reports and comparable with the smallest melt blown nonwoven fibers produced commercially. Coupled with the advantages of cross-linked fibers made by in-situ photopolymerization, the capability to produce small fibers with tailored diameter distributions by centrifugal spinning could further establish this technology as a competitive alternative to existing approaches. [ABSTRACT FROM AUTHOR]

Diglycidyl ether of bisphenol A (DGEBA) is among the most popular and widely used epoxy monomers. This monomer is commonly used in thermal network polymerizations with amines, phenols, isocyanates or mercaptans as curing agents. However, the photoinitiated polymerization of DGEBA is very sluggish and hence finds little use in high-speed photocuring applications. In this contribution, we demonstrated that this monomer can undergo very fast visible-light photopolymerization when combined with a silsesquioxane (SSO) functionalized with reactive epoxycyclohexane groups. The SSO was synthesized via alkoxysilane hydrolysis/condensation chemistry, using DGEBA as a solvent. We found that the photopolymerization of DGEBA is markedly accelerated as the amount of SSO in the mixture is increased. The promoter effect on the reactivity of DGEBA was ascribed to a combination of both thermal and copolymerization effects. Using dynamic mechanical analysis, we demonstrated that the resulting hybrid materials present a single-phase network structure, where the SSO species function as highly multifunctional epoxy reactants. [ABSTRACT FROM AUTHOR]

Reversible addition-fragmentation chain transfer (RAFT) processes in polymer systems have shown great utility in controlling radical polymerizations. Due to the reversible chain transfer mechanism, RAFT agents have been extensively used to synthesize monodisperse linear polymers and block copolymers in solution or emulsion polymerization. On the other hand, little is known about the effects of RAFT agents on the polymerization kinetics and thermo-mechanical properties of cross-linked materials. This work investigates the effect of RAFT agents on photopolymerization behavior and ultimate polymer properties in urethane acrylate systems. Our results indicate that RAFT agent addition has a significantly different impact on network development depending on inherent system characteristics, i.e., systems with glass transition temperature (T g) below room temperature (LT) or those with T g above room temperature (HT). When polymerizing with RAFT agents, photopolymerization rate decreases and can be tuned using different concentrations of RAFT agent. The final materials also show increased elongation at break with decreased Young's modulus. However, ultimate thermo-mechanical behavior and mechanical properties are different based on T g. With RAFT addition decreased T g is observed from HT polyurethane networks. Tensile toughness is also doubled in comparison to neat HT films. On the other hand, although the T g of RAFT modified LT polyurethane networks does not change significantly, toughness of the final polymer films varies significantly with RAFT agent concentration. Enhanced toughness is only observed from films with low RAFT agent concentration while toughness decreases with higher loading of RAFT agent. These results demonstrate that the polymer network and thermo-mechanical properties can be modified by introducing RAFT agent which enables dynamic polymer chain rearrangements in both LT- and HT-acrylate network systems. [Display omitted] • Photopolymerization rates are much higher in RAFT controlled high T g systems. • Addition of RAFT agents decreases cross-link density and T g. • RAFT modification enables significantly increased elongation. • RAFT modified high T g systems maintain tensile modulus and enhance toughness. [ABSTRACT FROM AUTHOR]

Thermoset initiator-free membranes are prepared by the UV-induced photopolymerization of thiol and (meth)acrylic monomers having polyethylene oxide chains, being known that the use of such monomers can lead to the formation of readily degradable membranes. The photopolymerization of different formulations is studied and the influence of the addition of a monofunctional methacrylate is investigated. By incorporation of lithium bis(oxalate)borate salt, solid polymer electrolytes are prepared and used as electrolyte membranes in Li-ion batteries. The ionic conductivity of the samples is measured and correlated to their thermal characteristics. The best performing sample shows encouraging cycling behaviour when tested in a truly-solid state lab-scale lithium test cell, thus enlightening the promising prospects of the newly designed polymer electrolytes. Furthermore, a preliminary degradation study is performed demonstrating the possibility to hydrolytically degrade the proposed UV cured networks making them extremely appealing for the development of sustainable and easily recyclable, thus greener, energy power sources. [ABSTRACT FROM AUTHOR]

Creating patterns of biomolecules and cells through precise surface engineering has offered the potentials for cancer-related studies, cellular bioassays, and drug screening because of the regulated cellular functions via the cell-substrate interactions. It is desirable in the basic laboratories with limited facilities to make the patterned surfaces by a template-free, low-cost, and high-throughput patterning technique. Here, thermo-responsive micropatterned surface was fabricated by solid photopolymerization of N-isopropylacrylamide (NIPAAm) crystals in the presence of photoinitiator and crosslinking reagent. A series of analytical tools were used to characterize the micropatterned surface for thorough understanding the pattern formation. The patterned NIPAAm crystals were created by inducing divergently needle-like monomer crystal growth from saturated monomer solution triggered by single or multiple seed crystals. Since NIPAAm crystals might have densely packed crystalline structure and effectively suppress oxygen diffusion from the environment, semicrystalline PNIPAAm films were easily obtained under UV irradiation in air without inert atmosphere protection. Subsequently, water immersion at room temperature for hours allowed the semicrystalline PNIPAAm film to form amorphous hydrogel with microscale features for cell morphology studies and heterotypic cell-substrate interactions. Microscopic visualization of human mesenchymal stem cells (hMSCs) cultured on the micropatterned PNIPAAm film exhibited significant elongation of hMSCs and nucleus along with the micropatterned features. The immunocytochemistry assay for heterotypic cancer cells on the micropatterned film not only provided the experimental evidence of cell harvesting by local heating/cooling treatment, but also demonstrated the identification of the specific cell type within heterotypic cell populations. [ABSTRACT FROM AUTHOR]

Poly( l -lactic acid) (PLLA) microfibers were surface functionalized by graft photopolymerization of 2-hydroxyethyl methacrylate (HEMA) onto the fiber surface. Grafted fibers were easily dispersed in enzymatically gelling tyramine-substituted gelatin, forming a homogeneous dispersion without hindering subsequent gelatin crosslinking. The obtained injectable hydrogels showed improved mechanical properties compared to analogues based on non-modified fibers. The composite with 1% (w/v) of surface modified fibers had a three-fold higher shear storage modulus (535.2 ± 90 Pa) than pure gelatin (184.9 ± 32 Pa) while no significant increase was observed in the case of non-grafted fiber composites. Moreover, PHEMA grafting on PLLA fibers did not compromise cell viability and proliferation within the hydrogel. The new injectable hydrogels offer improved potential as substrates for the regeneration of soft tissues. [ABSTRACT FROM AUTHOR]

In this work, an individual microgel particle dispersed in a viscous-like matrix was synthesized through the in-situ photopolymerization process. The actual size of the individual microgel particle was calculated based on the microscopic techniques. The cooperative relaxation properties of the individual microgel particle were studied using dynamic mechanical analysis technique. A value of 18 of dynamic fragility index for the microgel network was obtained. The size of cooperatively rearranging region (CRR) at the glass transition temperature for the microgel particle was estimated to be 6. A value of 0.041 mol/cm 3 of cross-link density of the individual microgel particle was predicted based on the atomic force microscopy results and stress-strain data. The microgel hardness was measured by a nano-indentation instrument with an indenter diameter of 150 nm. The value of the hardness of the microgel particle was found to be in a suitable agreement with the results obtained from the atomic force microscopy technique. On the basis of a proposed model, the apparent diffusion coefficient of Cl − through the photopolymerization-induced microgel particle was calculated to be about 10 μm 2 / s ec. [ABSTRACT FROM AUTHOR]

In this study, the fabrication of crosslinked nonwoven fibers via simultaneous thiol-ene photopolymerization and spinning of monomer jets has been demonstrated in centrifugal Forcespinning for the first time. We observed that simultaneous Forcespinning and photopolymerization resulted in a wide variety of fiber morphologies including beads, beads-on-string, uniform fiber, fused fibers, and well-cured fibers. To elucidate the underlying mechanisms and parameter interactions that give rise to these morphologies, we systematically varied the light intensity, solution elasticity, and spin speed of the Forcespinning process. From these experimental results, an operating diagram was constructed based on the measured process parameters, their respective timescales, and observed effects on fiber morphology. While numerous parameters can individually affect fiber formation and morphology, the interplay between curing kinetics, solution viscoelasticity, and orifice-to-collector processing time window is also crucial in this process. Smooth and well-cured fibers were formed only when the photopolymerization occurred sufficiently quickly, before both the breakup of fibers into droplets due to a surface tension driven Rayleigh instability and the deposition of fibers on the collector. Our findings can serve as a predictive guideline for the fabrication of crosslinked fibers with desired morphology, the implementation of the in-situ polymerization and spinning concept into other commercial fiber manufacturing technologies, and the adaptation of other functional or high performance monomer systems. [ABSTRACT FROM AUTHOR]

A fluorinated photoinitiator, namely perfluorooctanoyl acid 2- [4-(2-hydroxy-2-methyl-propionyl)-phenoxy]-ethyl ester (F-2959) was synthesized and characterized. To increase the polymerization rate, fluorine groups were connected to the benzene ring rather than the hydroxyalkyl. Real time FTIR analysis was taken to study the ability of F-2959 to overcome oxygen inhibition. UV–vis absorption spectroscopy, XPS, SEM, and multi-channel thermo detector were used to prove the migration of F-2959 in the formulations. During photopolymerization, the oxygen inhibition could be obviously decreased as the large amount of photoinitiator at the surface could consume oxygen in the air atmosphere. The fluorine compounds gathering on the surface also reduced the surface energy. By using this strategy, the film surface develops a wrinkled pattern with a low surface energy. And the wrinkled pattern may prove very useful in photopolymerization. [ABSTRACT FROM AUTHOR]

Polymerization-induced phase separation (PIPS) was studied in ambient photopolymerizations of triethylene glycol dimethacrylate (TEGDMA) modified by poly(methyl methacrylate) (PMMA). The molecular weight of PMMA and the rate of network formation (through incident UV-irradiation) were varied to influence both the promotion of phase separation through increases in overall free energy, as well as the extent to which phase development occurs during polymerization through diffusion prior to network gelation. The overall free energy of the polymerizing system increases with PMMA molecular weight, such that PIPS is promoted thermodynamically at low loading levels (5 wt%) of a higher molecular weight PMMA (120 kDa), while a higher loading level (20 wt%) is needed to induce PIPS with lower PMMA molecular weight (11 kDa), and phase separation was not promoted at any loading level tested of the lowest molecular weight PMMA (1 kDa). Due to these differences in overall free energy, systems modified by PMMA (11 kDa) underwent phase separation via Nucleation and Growth, and systems modified by PMMA (120 kDa), followed the Spinodal Decomposition mechanism. Despite differences in phase structure, all materials form a continuous phase rich in TEGDMA homopolymer. At high irradiation intensity (I o = 20 mW/cm 2 ), the rate of network formation prohibited significant phase separation, even when thermodynamically preferred. A staged curing approach, which utilizes low intensity irradiation (I o = 300 μW/cm 2 ) for the first ∼50% of reaction to allow phase separation via diffusion, followed by a high intensity flood-cure to achieve a high degree of conversion, was employed to form phase-separated networks with reduced polymerization stress yet equivalent final conversion and modulus. [ABSTRACT FROM AUTHOR]

Eosin, a photoreducible xanthene, reacts with tertiary amines and initiates the free radical photopolymerization of aqueous solutions of acrylate monomers. This reaction proceeds even in the presence of a large excess (∼1000×) of inhibiting oxygen via a mechanism that has not been established conclusively. This chemistry has proven useful in the area of biosensing, where the formation of a hydrogel on the time scale of seconds serves as a macroscopic, amplified signal that can be connected to molecular recognition events. In this work, we built a kinetic model to quantitatively explore a mechanism in which eosin is regenerated through the reaction of eosin-based radicals with peroxy-radicals formed from oxygen-inhibition reactions. To determine whether the predictions of this model are consistent with conversion profiles measured using real-time FTIR, we refrained from fitting rate constants or other unknown parameters associated with individual steps in the mechanism to the conversion profile. Rather, we considered physical upper bounds and performed sensitivity analyses spanning several orders of magnitude to predict the reactivity of the system. We explored the effects of the peroxy-mediated regeneration rate constant, k regen , and the initial eosin concentration on the irradiation time that is required to reach a C C bond conversion of 0.2 ( t 0.2 ). At this C C bond conversion, the aqueous monomer solutions studied herein have become hydrogels. The predictions of the model capture several trends that we have observed experimentally. However, even when the rate constants associated with eosin regeneration via reaction with peroxy-species are set at the physical upper bounds, the values of t 0.2 predicted by the model are much larger than those that we observed experimentally. The results presented herein motivate and provide a framework for future work to more fully elucidate the mechanism of this interesting and useful photopolymerization reaction. [ABSTRACT FROM AUTHOR]

A perylene bisimide derivative ( PDP-UPBIAcry ) having hydroxyl moieties at one termini and polymerizable acrylic units at the other termini was supramolecularly complexed with the pyridine units of Poly (4-vinyl pyridine) (P4VP), followed by photoinduced polymerization of the acrylic units to obtain lamellar organization in the <10 nm range. 1 H NMR studies including variable temperature (20 °C−70 °C) measurements were undertaken in DMSO-d 6 (anhydrous, extra dry) to understand the interaction between PDP-UPBIAcry and P4VP. The aromatic perylene protons of PDP-UPBIAcry registered an upfield chemical shift while the pyridine protons of P4VP exhibited small downfield shift in their 1:1 supramolecular complex. The hydrogen bonding interaction between pyridyl nitrogen and phenolic OH group was also traced in non-polar media like CDCl 3 in model complexes of 4-vinyl pyridine (4VP) with PDP-UPBIAcry . Wide angle X-ray diffraction (WXRD) technique was used to study the bulk structure. Transmission electron microscopy (TEM) imaging revealed highly ordered layered assembly formed upon complexation. Observation from DFT energy minimization studies were correlated with X-ray diffraction data of the supramolecular complex [ P4VP (PDP-UPBIAcry)] 1.0 to understand the nature of packing of PDP-UPBIAcry that lead to the formation of highly ordered lamellar stacks alternating with P4VP. The higher ordering in the supramolecular polymer complex was also confirmed by the quenching of fluorescence and reduced fluorescence life times of thin solid films of the [ P4VP Poly(PDP-UPBIAcry)] 1.0 sample. [ABSTRACT FROM AUTHOR]

Epoxides bearing vinyl groups bonded to one of the carbon atoms of the three-membered ring, exhibit the ability to dramatically increase the rate of the photoinitiated cationic polymerization of 3-mono- and 3,3-disubstuted oxetanes by eliminating or sharply reducing the length of the induction periods. This effect, termed by us as “kick-starting”, results from the ability of the aforementioned epoxides to undergo ring-opening on protonation to yield resonance stabilized allylic carbocations. Several examples are given of “kick-starting” epoxides together with their use in the photopolymerization of various oxetane monomers. [ABSTRACT FROM AUTHOR]

We report on a facile and reliable preparation of polypyrrole vessel structures modified with gold nanoparticles that are able to encapsulate organic molecules of biological importance. The polymer is coated onto the surface of aqueous droplets through photopolymerization of the monomer. When gold nanoparticles and/or biomolecules are contained in the droplets, these species become incorporated within the formed polymer microvessels. Herein, we provide thorough physicochemical characterization of the polymer structures including electron and optical microscopy, spectroscopy (steady state and time-resolved fluorescence, XPS, XRF) and other experimental techniques. Polymer microvessels are promising as smart drug carriers for new experimental therapies. As model drugs we use mRNA cap analogs which are nucleotide-derived compounds that have been shown to be potential anti-cancer agents. We demonstrate that embedding the metallic nanoparticles within the microvessels provides usefully high contrast in micro-computed tomography (microCT) which is promising from the standpoint of monitoring the fate of administered drug carriers inside the body. Moreover, our in vivo studies on rats demonstrate that intravenous administration of the microvessels does not evoke acute toxicity or death of the animals. [ABSTRACT FROM AUTHOR]

It has been well documented that self-assembly of block copolymers (BCP) in selective solvents, where the core-forming block is a crystallizable polymer, results in micelle structures with exceptional aggregation morphologies determined mainly by the crystallization energy from the core. In this contribution, we apply this concept to create ribbon-like nanostructures dispersed in an epoxy network. The selected system was a polyethylene- b -poly(ethylene oxide) (PE- b -PEO) diblock copolymer in an epoxy monomer based on diglycidyl ether of bisphenol A (DGEBA). This system was selected on the bases that PEO is an epoxy-philic block which is completely miscible with DGEBA before and after curing reaction whereas PE is a crystallizable epoxy-phobic block. Under these conditions, we access to self-assembled nanostructures with semicrystalline core before curing reaction. With the aim of preserving the structural features of these micelles, the epoxy monomers were cured at room temperature (i.e., below the melting transition of the core-forming PE block) by photoinitiated cationic ring-opening polymerization. Long nanoribbons dispersed in the cured epoxy matrix were obtained, as characterized by SAXS patterns and TEM images. These ribbon-like micelles present a tendency to aggregate resulting in the formation of face-to-face stacking of parallel micelles. We demonstrated that while the stacking number decreases with decreasing BCP concentration, the arrangement of the nanoribbons within one stack becomes less organized. [ABSTRACT FROM AUTHOR]