Amount Of Photoinitiator Research Articles

Photocured conductive PANI/acrylate composites for digital light processing. Influence of HDODA crosslinker in rheological and physicochemical properties

The design of novel photocurable conductive acrylic composites demands thorough research to find appropriate balance between the relative concentrations of monofunctional/ multifunctional monomers, photoinitiators and conductive filler, besides adjusting polymerization conditions. Likewise, when an intrinsically conductive polymer such as polyaniline (PANI) is selected as conductive filler, the homogeneous distribution of its nanometric aggregates is essential to prevent heterogeneous curing due to its strong UV absorption. In this work, the influence of PANI-HCl on the physical properties of acrylic composites based on Ethyleneglycolphenylether acrylate (EGPEA) and Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), photoinitiator, was examined in the frame-work of the percolation model. Rheological testing combined with Scanning Electron Microscopy (SEM) were used for efficient control of the filler dispersion in order to better understand the electrical conductivity-structure behaviour. Infrared Spectroscopy probed the degree of monomer conversion and the filler interaction with the polymer matrix, whereas the thermal properties were evaluated with the aim of establishing the maximum working temperatures. Above the percolation threshold, the formulation with 4.8 wt% PANI was selected as the most suitable composition achieving maximum conductivity (10-3 S cm−1) at the lowest PANI content. The problem of excessive aggregation of PANI clusters was tackled by the addition of a 15 wt% of the reactive diluent 1,6-hexanediol diacrylate (HDODA) to the previous formulation. The outcomes were improved dispersion and better integration of PANI nanorods within the acrylic matrix plus a smoother film surface, while retaining high electrical conductivity. The viscosity of the selected prepolymer formulations and penetration depth of UV photons gave encouraging results for the use of the developed compositions as anticorrosion coatings, digital light processing (DLP) or piezoelectric sensors. The high critical cure dosages obtained will be easily overcome by adjusting the type and/or amount of photoinitiator.

A mechanically enhanced electroactive hydrogel for 3D printing using a multileg long chain crosslinker

Electroactive hydrogels (EAHs) are receiving attention in soft robotics. 3D printing makes EAHs even more attractive, due to the diversification and elaboration of actuations. However, 3D printing needs a large amount of photoinitiator for faster printing, which makes the printed hydrogels so brittle that they cannot produce large scale 3D printing. Here, we developed a 3D printable EAH based on poly(3-sulfopropyl acrylate, potassium salt) (PSPA) using glycidyl methacrylated hyaluronic acid (GMHA) as a mechanically enhancing multileg long chain (MLLC) crosslinker. The MLLC crosslinking improved the stretchability of the PSPA-based hydrogel to 49% from 28%, while maintaining the same level of electroactivity. Additionally, the fracture toughness of the PSPA-based hydrogel remarkably increased from 11 to 40 J m−2 with crosslinking by the MLLC. Using the mechanically enhanced EAH, i.e. the GMHA–PSPA EAH, the 3D printing of elaborate structures, e.g. ‘Leaning Tower of Pisa’ and a hand, and their electroactuation were successfully demonstrated.

Impact of co-doping concentration in copolymer network liquid crystals

ABSTRACTThe impact of varying the co-doping concentration of a mesogenic and a non-mesogenic monomer in the reactive mixtures used to create a copolymer network LCs was investigated. Use of copolymer has been found to improve the response properties in the obtained liquid crystal composites. The polymer network in the studied copolymer network LCs was examined by scanning electron microscopy and the response times in various samples were investigated. Samples were prepared with various reactive mixtures, each of which had a constant concentration of mesogenic monomer, various concentrations of non-mesogenic monomer, and the same amount of photoinitiator. These reactive mixtures were filled in home assembled test cells with planar alignment and then exposed to UV light. With increasing concentration of the non-mesogenic monomer, the response properties of the resulting copolymer network LC were improved. Usually, if the overall polymer content in a polymer network LC is increased, the threshold voltage is also increased. However, both threshold voltages and response times were lowered and the response properties were thus improved in the studied copolymer network LCs. This unexpected behavior could be traced back to inducing a grainy polymer morphology of the copolymer network by using a non-mesogenic monomer.

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region.

Recent progresses achieved in terms of synthetic procedures allow now the access to polymers of well-defined composition, molecular weight and architecture. Thanks to these recent progresses in polymer engineering, the scope of applications of polymers is far wider than that of any other class of material, ranging from adhesives, coatings, packaging materials, inks, paints, optics, 3D printing, microelectronics or textiles. From a synthetic viewpoint, photoredox catalysis, originally developed for organic chemistry, has recently been applied to the polymer synthesis, constituting a major breakthrough in polymer chemistry. Thanks to the development of photoredox catalysts of polymerization, a drastic reduction of the amount of photoinitiators could be achieved, addressing the toxicity and the extractability issues; high performance initiating abilities are still obtained due to the catalytic approach which regenerates the catalyst. As it is a fast-growing field, this review will be mainly focused on an overview of the recent advances concerning the development of organic and organometallic photoredox catalysts for the photoreticulation of multifunctional monomers for a rapid and efficient access to 3D polymer networks.

Combining cure depth and cure degree, a new way to fully characterize novel photopolymers

Bottom-up stereolithography has become a common lithography-based additive manufacturing technology (L-AMT) to fabricate parts with high feature resolution for biomedical applications. Novel vinyl ester based photopolymers, with their good biocompatibility and biodegradation behavior, showed a promising capacity as bone replacement materials. Due to further tuning of the mechanical properties, those biophotopolymers exhibit reduced curing speed in comparison to highly crosslinked resins e.g. acrylates. The slow structuring of the polymer network results in difficulties at the printing process. The Jacobs working curve characterizes the cure- and penetration depth of resins, but gives no information about the mechanical properties of the cured layer. The information of cure depth and the mechanical properties of the cured layer (cure degree) is desired. In this work, the conditions at L‑AMT during the structuring process were simulated with a real-time near-infrared photorheometer to evaluate the cure degree of a cured layer at constant cure depth. Therefore, we investigated the curing behavior of mixtures with variable amount of photoinitiator (PI) and light absorber (LA) of vinyl ester based biophotopolymers. We found, that a high amount of LA is crucial for good mechanical properties at constant cure depth. Moreover, we present a technique how to optimize a resin formulation regarding the content of PI and LA.

Morphology, electro-optical and dielectric properties of polymer network liquid crystals in visible wavelengths

ABSTRACTThe correlations among electrical, optical properties and polymer morphologies of polymer network liquid crystals (PNLCs) constructed with various curing parameters are investigated. The experimental results indicate that high UV curing intensity, low curing temperature and high monomer-dopant concentration reduce the sizes of liquid crystal (LC) domains, thereby decreasing field-off response time and light scattering and increasing phase retardation of the PNLC cells. Photoinitiator concentration affects the LC domain size as well. For instance, increase in photoinitiator concentration results in the acceleration of polymerisation and thus decreases LC domain size. This effect increases driving voltages of the PNLC cells. Notably, excessive amounts of photoinitiator increases the LC domain size of the PNLC cell. Furthermore, dielectric measurement reveals that decrease in the LC domain size generally increases the dielectric relaxation frequency of the PNLC cells. When the LC domain size is small enough, the dielectric relaxation frequency of the PNLC cell is further dominated by the monomer concentration owing to the increased densities of polymer networks that facilitate the alignment of LC molecules.

可視光線重合型レジンの重合率に関する基礎的研究 : 触媒組成と重合率との関係(I)

可視光線重合型レジンの重合率に関する基礎的研究 : 触媒組成と重合率との関係(I)

Manipulating the Surface Structure of Hybrid UV Curable Coatings through Photopolymerization‐Induced Phase Separation: Influence of Inorganic Portion and Photoinitiator Content

AbstractSurface topography and phase‐manipulated distribution of hybrid UV curable coatings is performed. Accordingly, phase separation is controlled by changing the inorganic/organic ratio and the photoinitiator content as these are the main thermodynamic and kinetic affecting factors, respectively. Chemical and mechanical evolution of the samples during photopolymerization is investigated by time‐resolved Fourier transform infrared spectroscopy and photorheometry, respectively. It is found that the samples that contain larger portion of inorganic oligomers are polymerized faster, but undergo gelation later; this provides them more time to undergo phase separation prior to gelation. Therefore, their surfaces become rougher and more heterogeneous, which is confirmed by atomic force microscopey. Furthermore, adding larger amounts of photoinitiator into the samples leads to them being photopolymerized faster and undergo gelation at lower conversion. So, they have less time and thermodynamic tendency to undergo phase separation prior to gelation; their surfaces thus become smoother and more homogeneous.

Preparation of biomimetic photoresponsive polymer springs.

Polymer springs that twist under irradiation with light, in a manner that mimics how plant tendrils twist and turn under the effect of differential expansion in different sections of the plant, show potential for soft robotics and the development of artificial muscles. The soft springs prepared using this protocol are typically 1 mm wide, 50 μm thick and up to 10 cm long. They are made from liquid crystal polymer networks in which an azobenzene derivative is introduced covalently as a molecular photo-switch. The polymer network is prepared by irradiation of a twist cell filled with a mixture of shape-persistent liquid crystals, liquid crystals having reactive end groups, molecular photo-switches, some chiral dopant and a small amount of photoinitiator. After postcuring, the soft polymer film is removed and cut into springs, the geometry of which is determined by the angle of cut. The material composing the springs is characterized by optical microscopy, scanning electron microscopy and tensile strength measurements. The springs operate at ambient temperature, by mimicking the orthogonal contraction mechanism that is at the origin of plant coiling. They shape-shift under irradiation with UV light and can be pre-programmed to either wind or unwind, as encoded in their geometry. Once illumination is stopped, the springs return to their initial shape. Irradiation with visible light accelerates the shape reversion.

Iron Complexes in Visible‐Light‐Sensitive Photoredox Catalysis: Effect of Ligands on Their Photoinitiation Efficiencies

AbstractThe novel role of metal‐based complexes as photoinitiator catalysts fits well into the concept of green chemistry, as it realizes the activation of polymer synthesis processes by visible light that are abundant in the solar light and allows the marked reduction of photoinitiator amount in the systems. In the present paper, a series of iron complexes (FeC_x) with various ligands have been proposed as new photoinitiator catalysts to initiate the cationic polymerization of epoxides or the free radical polymerization of acrylates upon a near‐UV or visible‐light LED exposure. The ligands play an important role on the light absorption properties and the photoinitiation ability of the iron complexes. In combination with one or two additives, FeC_x are capable to efficiently generate radicals, cations, and radical cations through an oxidative or a reductive path. Two of the newly developed FeC_x‐based photoinitiating systems exhibited comparable photoinitiation efficiency with the commercial Type I photoinitiator bis(2,4,6‐trimethylbenzoyl)‐phenylphosphineoxide (BAPO). Owing to the photocatalytic effect, remarkable photoinitiation efficiencies have been achieved by using very low concentration of iron complexes (0.02 wt %) in the systems. The involved photochemical mechanisms have been studied using electron spin resonance spin trapping, steady state photolysis, cyclic voltammetry, and laser flash photolysis techniques.

Preparation of Poly(Lactic Acid) Acrylate for UV-Curable Coating Applications

UV-curable process is widely used for paints, inks and adhesives due to its rapid curing, low energy consumption, high efficiency and low volatile organic compounds (VOCs). The objective of this research is to prepare poly(lactic acid) (PLA) based UV-curable coating by using glycolyzed PLA. PLA was glycolyzed by ethylene glycol (EG) at 170°C for 90 minutes. The obtained glycolyzed PLA was reacted with methacrylic anhydride (MAAH) to provide PLA acrylate oligomer. The obtained PLA acrylate oligomer was used in coating formulations with various amounts of photoinitiator and cured under UV radiation. Physical properties of cured coating film were investigated such as pencil hardness, gloss and haze. The results showed that poly(lactic acid) (PLA) based UV-curable coating provided good physical properties.

A fluorinated compound used as migrated photoinitiator in the presence of air

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.

액상 이소프렌 고무가 자외선 경화형 아크릴 점착제의 점착 특성에 미치는 영향

In this study, the acrylic pressure sensitive adhesive (PSA) for the optical functionality sheet was prepared by blending liquid isoprene rubber. The acrylic PSA was synthesized with butyl acrylate, acrylic acid, 2-ethylhexyl acrylate and 2-hydroxyethyl methacrylate. Toluene was used to a solvent for polymerization. Liquid isoprene rubber (LIR-50) was blended with the acrylic PSA and blend ratio was 0 ~ 50 wt%. According to the results, the adhesive transfer, which was the big problem of acrylic adhesive, was reduced with the addition of LIR-50. The secondary bonding of LIR-50 with substrate did not occurred due to absence of polar group in LIR-50. The peel strength and adhesive transfer were decreased by UV curing and the degreed of decrease depended on the amounts of photoinitiator and UV irradiation time. On the other hand holding power increased drastically by increasing amounts of photoinitiator and UV irradiation time.

Synthesis of Polystyrene-Based Hyperbranched Polymers by Thiol–Yne Chemistry: A Detailed Investigation

This contribution reports on the preparation of hyperbranched polymers via thiol–yne photopolymerization of macromolecules bearing a thiol group at one of their chain end and an alkyne moiety at the other. These thiol/yne macromonomers were produced by the reversible addition–fragmentation chain transfer (RAFT) polymerization of styrene mediated by an alkyne-containing chain transfer agent, followed by the aminolysis of the trithiocarbonate groups into thiol moieties. The first part of this report concentrates on studying the effects upon the thiol–yne photopolymerization process caused by the variation of several experimental conditions, such as the size of the thiol/yne macromonomer utilized, the amount of photoinitiator added, or the initial concentration of macromonomer used. Among the various parameters investigated, the latter was demonstrated to be the leading factor that contributes to the final size of the hyperbranched structures. The second part of this article discusses the multidetector size-exclusion chromatography (SEC) analysis of the materials obtained by thiol–yne photopolymerization. This analytical technique allows the molecular weight of the hyperbranched polymers to be determined and the hyperbranched topology to be confirmed, as highlighted by the increased density of the materials compared to that of linear equivalents of the same chemical composition and identical molar masses.

Cyclic Olefin Copolymer/Photoinitiator Proton Exchange Membranes for Direct Methanol Fuel Cells

This article investigates cyclic polyolefin copolymer/photoinitiator blend membranes that contain 10, 30, and 50 PHR (parts per hundred resins) cationic photoinitiator (PI) used in direct methanol fuel cells. We analyze the morphology, electrical, methanol barrier, mechanical and thermal properties of COC/PI-blend membranes. The results show that superacid photoinitiators can enhance the conductivity and methanol barrier of COC. However, the mechanical properties decrease with the amount of photoinitiator. COC/PI blend membranes have heat stability below 200°C. They can meet the direct methanol fuel cells operating temperatures.

Photopolymerisation and characterization of maleylatedcellulose-g-poly(acrylic acid) superabsorbent polymer

A novel biodegradable superabsorbent polymer has been prepared from maleylated cotton stalk cellulose (MCSC) crosslinker and acrylic acid (AA) by ultraviolet (UV) photopolymerization in aqueous solution at room temperature, and irgacure 651 as a photoinitiator. The resulting superabsorbent was characterized by FT-IR, 1H NMR, SEM and TGA. The effects of preparation conditions such as degree of substitution (DS), amount of maleylated cotton stalk cellulose, exposed time, photoinitiator amount and monomer concentration on the water absorbency and the monomer conversion in graft were evaluated. The swelling kinetics, salt-resistance, water retention capacity and biodegradability of the MCSC-g-PAA superabsorbent were investigated. It was found that, the obtained superabsorbent have good swelling degree that greatly affected by its composition and preparation conditions. Owing to its considerable good water retention capacity, being economical and environment-friendly, it might be useful for its application in agriculture field.

Photocrosslinked poly(ester‐anhydride) microspheres with macroporous structure

In this work, the new method of preparation biodegradable microspheres with macroporous structure is presented. Typical methods used for generation of porous structures in microspheres obtained from preformed polymers require the use of additional substances acting as porogens. In this study, the porosity was achieved as the effect of photocrosslinking, without porogens. Microspheres were prepared using emulsion solvent evaporation technique from functional poly(ester‐anhydride)s with different amount of allyl groups in the side chains. The crosslinking was carried out by UV irradiation during the solvent evaporation (photoinitiator was introduced to polymer solution). The size of microspheres obtained was in the range of 1.7 – 4 µm (small microspheres) or 31 – 50 µm (large ones) and depended on the conditions used in emulsion formulation process. Effectiveness of the crosslinking was characterized by the content of insoluble part of samples, and it was in the range of 42–89%. The content of insoluble part of sample of microspheres and their porosity were dependent on functionality of poly(ester‐anhydride)s, the amount of photoinitiator used, and also on size of microparticles. The small particles were always more crosslinked than the large ones, but the latter were more porous than the small ones. Crosslinked microparticles indicated higher loading efficiency of model compound and appeared to degrade faster than uncrosslinked ones, probably due to their high porosity. The high porosity of microspheres obtained would enable their eventual use in pulmonary drug delivery systems or in construction of porous scaffolds for tissue engineering. Copyright © 2013 John Wiley & Sons, Ltd.

Constructing Robust and Functional Micropatterns on Polystyrene Surfaces by Using Deep UV Irradiation

We report the preparation of different surface patterns based on the photo-cross-linking/degradation kinetics of polystyrene (PS) by using UV light. Upon exposure to UV light, PS can be initially cross-linked, whereas an excess of the exposure time or intensity provokes the degradation of the material. Typically photolithography employs either positive or negative photoresist layers that upon removal of either the exposed or the nonexposed areas transfer the pattern of the mask. Herein, we present a system that can be both negative and positive depending on several aspects, including the irradiation time, intensity, or presence of absorbing active species (photoinitiators) using a general setup. As a result of the optimization of the time of exposure and the use of an appropriate cover or the incorporation of an appropriate amount of photoinitiator (in this particular case IRG 651), different tailor-made surface patterns can be obtained. Moreover, changes of the chemical composition of the polystyrene using, for instance, block copolymers can lead to surface patterns with variable functional groups. In this study we describe the formation of surface patterns using polystyrene-block-poly(2,3,4,5,6-pentafluorostyrene) block copolymers. The introduction of fluorinated moieties clearly modifies the wettability of the films when compared with that of the same structures obtained with PS. As a consequence we present herein a patterning methodology that can simultaneously vary not only the morphology but also the surface chemical composition.

Preparation and Properties of Ecological Colored Cellulose Material

Ecological colored cellulose material was prepared via UV initiated photografting of acrylic acid/cationic dye system in this study. The colored cellulose material was characterized using scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). The effects of monomer concentration, photoinitiator amount, dye amount, pH value, grafting time, heating temperature and grafting method on the coloration of cellulose material were discussed. The results showed that the optimum process was as follows: the monomer concentration of 50wt%, photoinitiator amount of 3o.w.m.%, grafting time of 4min, and heating temperature of 70.

Facile and efficient synthesis of hyperbranched polyesters based on renewable castor oil

Hyperbranched polyesters with thioether linkages were facilely prepared from methyl 10-undecenoate, a castor oil-derived renewable chemical. The monomer was obtained in excellent yield through thiol–ene click chemistry in the presence of catalytic amounts of photoinitiator under UV irradiation. Subsequent bulk polycondensation via a transesterification process catalyzed by Ti(OBu)4, Sb2O3 or Zn(OAc)2 gave hyperbranched polyesters with high molecular weights and unusual crystalline properties. The degree of branching in the range 0.45 − 0.54 calculated from quantitative 13C NMR spectroscopy and low inherent viscosities of 0.16 − 0.25 dL g−1 strongly confirmed the hyperbranched structures of the resultant polymers. © 2012 Society of Chemical Industry