Photopolymerization Reaction Research Articles

A novel method for PEGylation of chitosan nanoparticles through photopolymerization.

An ultrafast and convenient method for PEGylation of chitosan nanoparticles has been established through a photopolymerization reaction between the acrylate groups of PEG and methacrylated-chitosan nanoparticles. The nanoparticle characteristics under physiological pH conditions were optimized through altered PEG chain length, concentration and duration of UV exposure. The method developed here has potential for clinical translation of chitosan nanoparticles. It also allows for the scalable and fast synthesis of nanoparticles with colloidal stability.

Coumarin derivatives as versatile photoinitiators for 3D printing, polymerization in water and photocomposite synthesis

The goal of this paper concerns the first evaluation of two recently reported coumarins to initiate photopolymerization reactions.

Mechanics of shape distortion of DLP 3D printed structures during UV post-curing.

Digital light processing (DLP) three-dimensional (3D) printing technology has advantages of fast printing speed and high printing precision. It can print objects with small and complex geometrical features and has been widely used in jewelry manufacturing and dentistry. In DLP printing, it is common to use post-treatment with UV light irradiation to improve the final mechanical properties. However, it was found that the UV post-curing process can lead to shape distortion and thus reduction of dimension accuracy. In this paper, we combined photopolymerization reaction kinetics and Euler-Bernoulli beam theory to study UV post-curing induced shape distortion of thin structures prepared by DLP 3D printing. Experiments were conducted to characterize the evolution of mechanical behavior of printed samples during the post-printing process, which was correlated to printing parameters (printing time of single-layer, height of single-layer and printing UV intensity), post-curing UV light intensity and the thickness of the strip. Moreover, post-curing induced distortion was used for the fabrication of 3D structures.

Solid or gel? Which one works better for [2 + 2] photochemical polymerization in pyridine appended flexible phenylene 1, 4-bis-olefins by Ag(i) templation?

Two diene molecules were shown to undergo photopolymerization reactions in their metal-organic gels and xerogels, while their respective crystalline CPs are photostable. These reactions reveal the advantages of the gels and xerogels compared to their crystalline counterparts and also the utility of AgAg interactions in the gels to promote topochemical polymerizations.

Photo-differential Scanning Calorimetry Study on Photopolymerization of Polyacrylate/E7 Liquid Crystal Blends

Photo-differential scanning calorimetry (photo-DSC) was used to investigate the cure kinetics of a photo-initiated polymerization of tripropylene glycol diacrylate (TPGDA) monomers mixed with a eutectic liquid crystal mixture, E7, chosen due to its significant optical properties. The thermal photo-polymerization reactions were performed in isothermal mode in order to identify and evaluate the different thermal effects occurring during the photo-polymerization reaction under UV light. The results obtained help to better understand the curing mechanisms as well as the kinetics of the curing reactions. The isothermal photo-DSC provided complex thermograms showing the presence of two thermal effects: an exothermic heat (positive activation energy) generated during the conversion of monomers and an endothermic heat produced by the UV lamp. The latter phenomenon was observed in our previous work and was associated to the heating of the polymer dispersed liquid crystals (PDLC) material by the UV irradiation lamp. The dependence of photopolymerization on the time and intensities of the curing UV light were investigated. The results showed that the high intensity UV light heats the material and slows the process of phase separation which, in turn, affects the electro-optical properties of the material under study. The photo DSC results also revealed that the heating of the system was insignificant and can, therefore, be neglected, for materials exposed to UV radiation with an irradiation time of 5 seconds and a low intensity of 13.80 mW/cm2.

Dissymmetry enhancement in enantioselective synthesis of helical polydiacetylene by application of superchiral light

Superchiral light, generated by the interference of two counter-propagating circularly polarized light (CPL) with same frequency, opposite handedness and different intensity, exhibits enhanced dissymmetry in its interaction with chiral molecules, and has the potential for ultrasensitive detection and characterization of chiral molecules. It is anticipated that the enhanced optical dissymmetry in superchiral light (SCL) field may be utilized to promote asymmetric photochemical reactions efficiency. Herein we reported SCL impart greater chiral bias to trigger asymmetric photo-polymerization reaction from initially achiral diacetylene (DA) monomer, and the enhanced optical dissymmetry for whole polydiacetylene (PDA) films could be achieved. An explanation based on the chiral transfer and amplification of chiral bias from SCL during the polymerization process has been proposed. Moreover, thus formed chiral PDA films polymerized by SCL exhibited enhanced enantioselective recognition ability, and can serve as a direct visual probe for the discrimination of some specific enantiomers.

Polymerization Rate Modulated by Tetraarylborate Anion Structure: Direct Correlation of Hammett Substituent Constant with Polymerization Kinetics of 2-Hydroxyethyl Methacrylate

A series of para-substituted tetraarylborates were investigated as aryl radical generator for photopolymerization reactions, using 2-hydroxyethyl methacrylate as monomer. The first steps of the photopolymerization process involve the use of tetraarylborate as monocomponent photoinitiator or combination of two-component systems (riboflavin and tetraarylborate anion) to generate the aryl radical species, which is used to initiate the radicalar polymerization of vinyl monomers. Both photoinitiator systems herein investigated are very attractive for vinyl polymerization upon light irradiation. The polymerization and photochemical results indicate that the changes on the para-substituted ligand may be used to improve the formation of aryl radical species and the rate constant of electron transfer into two-component systems. In consequence of this reaction, the kinetics of radical polymerization is also modulated by electron donor/acceptor features of para-substituent ligands.

Metal-Organic Layers Efficiently Catalyze Photoinduced Polymerization under Visible Light.

A photosensitizing metal-organic layer (MOL), IrBPY-MOL, based on hafnium-oxo clusters and cyclometalated iridium-complex-derived organic linkers, was synthesized and used as an efficient catalyst for photopolymerization of methyl methacrylate and other monomers to afford polymers with high-number-averaged molar masses and low polydispersity indices. The corresponding metal-organic framework (MOF) failed to photopolymerize or exhibited low catalytic efficiency under identical conditions. This work highlights the advantages of MOLs over their MOF counterparts in overcoming pore-size and diffusion limitations in photopolymerization reactions.

First Detection of Photoinitiators and Metabolites in Human Sera from United States Donors.

Photoinitiators (PIs), including benzophenones (BZPs), thioxanthones (TXs), and amine co-initiators (ACIs), are commonly used in photopolymerization systems, and their contamination in foodstuffs and the environment is attracting attention. Although humans are likely exposed to PIs, no data on human burdens of these chemicals are available. In this study, 18 PIs were detected in 50 individual human serum samples with concentrations of ΣPIs (sum of the detected PIs) from 423 to 2870 pg/mL (geometric mean, GM: 836 pg/mL). ΣBZPs (231-1240 ng/g,; GM: 593 pg/mL) were the dominant components, while ΣTXs (21.0-1431 ng/g; GM: 145 pg/mL) and ΣACIs (11.3-976 ng/g; GM: 48.5 pg/mL) were much lower. Data analysis found significantly higher concentrations of most PIs in the male sera than in the female ( p < 0.05). ΣPIs (2921-4139 ng/g; GM: 3621 pg/mL) were also detected in five pooled serum samples, each from at least 1000 donors, indicating the prevalent human burdens of PIs in a large population. Human liver S9 biodegradations of representative PIs, 2-isopropylthioxanthone (2-ITX) and 2,4-diethylthioxanthone (DETX), were conducted. Hydroxylation, sulfoxide, and sulfone metabolites of DETX and 2-ITX were identified by high resolution mass spectrometry in human liver S9 incubation systems. With synthesized standards, the sulfoxide and sulfone metabolites were successfully detected in the human serum samples, which contributed substantially to total human burdens. The ubiquitous presence of PIs in human sera indicates significant human exposure to PIs, although photopolymerization reaction has been generally considered a green technology.

Nano-electrokinetic ion concentration in the ion enrichment zone

To reveal the internal discipline and accurately identify the inflection point, the Poisson–Nernst–Planck equations combined with the Navier–Stokes equation are employed and a method based on the horizontal angle of the tangent line and the distance from a pointcut to the origin is presented. Utilizing a micromachining technique and a photopolymerization reaction, a polyacrylamide gel plug is integrated into a microchannel to form a micro–nanofluidic chip. With the chip, FITC concentration experiments are developed with the initial concentration of 10 nM. Experimental testing confirms the results and demonstrates that the concentration is increased at first and then decreased with the increasing of the electric potential. That variation trend should be attributed to a balance between the repulsive force and the electrophoresis effect. The research results also demonstrate that upon increasing the voltage, the horizontal angle first decreases and then increases corresponding with the reverse trend of the distance. For a given micro–nanochannel, the peak ion concentration can be obtained through decreasing the horizontal angle and increasing the distance. The results will help determine peak voltage.

2018 Tess Award to Christopher Bowman; call for 2019 nominations

Christopher N. Bowman, the James & Catherine Patten Endowed Chair and a Distinguished Professor in the department of chemical and biological engineering at the University of Colorado, Boulder, is the winner of the 2018 Roy W. Tess Award in Coatings, sponsored by the ACS Division of Polymeric Materials: Science & Engineering. The $3,000 award recognizes outstanding contributions to coatings science, engineering, and technology. Bowman is being honored for his contributions to the understanding of photopolymerization systems and reaction engineering of cross-linked polymer systems. He will receive the award during the fall ACS national meeting in Boston. Nominations are being sought for the 2019 Roy W. Tess Award. Scientists from all sectors of industry, government, and academia are eligible to apply and should forward nominations to Theodore Provder, Tess Award chairman, at 5645A Emerald Ridge Pkwy., Solon, OH 44139. Upon receipt of names, Provder will request information on the nominee regarding

Additive-free photosynthesis of acrylamide hydrogels initiated with CdS and TiO2 as light visible nano-photocatalysts

Hydrogels are three-dimensional polymer networks which can be synthesized by different techniques, such as free-radical addition reaction which is the most well-known technique in functional vinyl monomer polymerization. Photopolymerization, as an attractive technique, has been used in radical polymerization of monomers and has revitalized interest in the idea that it congregates a wide range of economic and ecological expectations. Due to the spatial–temporal control and a mild curing process of polymerization, photoinitiator semiconductor nano-particles offer great advantages, such as effective and quantitative reaction. Cadmium sulfide nanowire, titanium dioxide (TiO2) nanotube, and TiO2 nanowire were used as visible photocatalysts for photopolymerization of acrylamide hydrogel without using any additive under the sunlight and purple LED irradiations. The effects of different synthetic parameters, including initiator type and concentration and type of light sources, were investigated to achieve hydrogels with maximum swelling capacity. The results showed that the swelling of hydrogel reached 80 g water/g hydrogel when the TiO2 nanowire was used as the photoinitiator. The synthesized semiconductors and hydrogels were characterized by X-ray diffractometry, adsorption isotherm, infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. According to the results, the new initiators led to semiconductor-based hydrogels, achieved with high swelling property through a high-speed high-efficient photopolymerization reaction in a safe manner.

A (Triphenylphosphine)Silver (I) Complex as a New Performance Additive in Free‐Radical Photopolymerization under Air

AbstractUnusual photochemical properties of an Ag(I)‐derived complex, i.e., bis[(µ‐chloro)bis(triphenylphosphine)silver (I)] ([Ag](PPh3)) are demonstrated when used in free‐radical photopolymerization reactions: i) [Ag](PPh3) can act as an innovative photoinitiating system when associated with a commercial type I photoinitiator 2,2‐dimethoxy‐2‐phenylacetophenone to overcome the oxygen inhibition effect during the free‐radical photopolymerization of acrylate monomers, thus accelerating the kinetics of polymerization under air; ii) silver‐based nanoparticles can be in situ generated under air, thus leading to new antibacterial coatings which prevent the growth of Escherichia coli and Staphylococcus aureus after few hours of incubation.

Additive Manufacturing of Transparent Silica Glass from Solutions.

A sol, aqueous solution-based ink is presented for fabrication of 3D transparent silica glass objects with complex geometries, by a simple 3D printing process conducted at room temperature. The ink combines a hybrid ceramic precursor that can undergo both the photopolymerization reaction and a sol-gel process, both in the solution form, without any particles. The printing is conducted by localized photopolymerization with the use of a low-cost 3D printer. Following printing, upon aging and densifying, the resulting objects convert from a gel to a xerogel and then to a fused silica. The printed objects, which are composed of fused silica, are transparent and have tunable density and refractive indices.

Tribological behaviors of the UV curing polyurethane acrylate resin- polytetrafluoroethylene bonded solid lubricating coatings filled with LaF3

The polyurethane acrylate resin-polytetrafluoroethylene (denoted as PUA/PTFE) bonded solid lubricating coatings with good tribological properties were prepared by ultraviolet radiation curing (UV curing), and then nano-LaF3 and micro-LaF3 were incorporated to further improve the tribological properties of the lubricating coatings. The photopolymerization reaction of the lubricating coating binder was characterized by an attenuated total reflection Fourier transform infrared spectrometer (ATR-FTIR). A micro-hardness tester was used to evaluate micro-hardness and a CSM friction and wear tester was selected to investigate the tribological properties of the lubricating coatings under dry friction condition. The coating surfaces and worn surfaces topography, as well as the distribution of La elements, were observed with a scanning electron microscope equipped with an energy dispersive X-ray spectrometer. Results show that the final conversion of acrylic double bond reached 98.4%, and the lubricating coating showed the best adhesive strength, micro-hardness and tribological properties when the mass ratio of PTFE to the binder was 1. Moreover, the incorporation of nano-LaF3 or micro-LaF3 both effectively enhanced the micro-hardness and the wear resistance of the PUA/PTFE lubricating coatings. Furthermore, nano-LaF3 was superior to micro-LaF3 for the improvement of anti-wear performance. The main wear mechanism of the UV curing PUA/PTFE lubricating coatings was dominated by fatigue wear.

Particle Rotation in Colloidal Processing under a Strong Rotating Magnetic Field.

Functional ceramics with oriented crystals prepared by colloidal processing in a strong magnetic field are expected to show improved functionality. In this study, the orientation rate of particles with low magnetic susceptibility in a concentrated slurry under a strong rotating magnetic field was experimentally demonstrated using a fast photopolymerization reaction. A slurry of (Sr,Ca)2NaNb5O15 particles dispersed in an ultraviolet curable resin with a catalyst was consolidated using UV irradiation under a strong rotating magnetic field. The degree of particle orientation increased with increasing processing time and became saturated after 20 s. The orientation time was observed experimentally; the period required to achieve particle orientation was proportional to the measured viscosity of the slurry and the inverse of the square of the magnetic flux density.

Preliminary study of the application of a novel hydrophobic photo-polymerizable nano-structured coating on concrete substrates

In order to improve of the durability of concrete from the attack of aggressive environments, a solvent-free hydrophobic photo-polymerizable organic–inorganic (O-I) nano-structured coating, indicated as HEP, was experimented on different concretes. The nano-structured hybrid product was already proved to act as an excellent hydrophobic protective coating for different natural stones. The outstanding properties of this novel system refer to the high reactivity of HEP at low-moderate temperatures, its eco-compatibility, being solvent-free, and preservation of its performance even after a severe environmental aging. The hybrid system was obtained starting from methacrylic-siloxane monomers, through a process involving hydrolysis and condensation steps. The cross-linking reactions of the acrylic monomers took place via free radical photo-polymerization reactions, activated by a suitable UV photo-initiator. The suitability of the un-reacted fresh system to be applied on concrete was first assessed through rheological analysis. Then, the liquid mixture, after its application on a glass substrate, was subjected to a dual curing procedure, consisting in a UV-polymerization step followed by a thermal stage. Different properties (i.e. Tg, transparency, scratch and surface hardness) were evaluated on the experimental coating. HEP was, then, applied on concrete substrates and its surface and protective characteristics were measured. Two different concretes were selected, i.e. based on Portland-limestone and pozzolanic cements.

Multihydroxy-Anthraquinone Derivatives as Free Radical and Cationic Photoinitiators of Various Photopolymerizations under Green LED.

Multihydroxy-anthraquinone derivatives [i.e., 1,2,4-trihydroxyanthraquinone (124-THAQ), 1,2,7-trihydroxyanthraquinone (127-THAQ), and 1,2,5,8-tetrahydroxyanthraquinone (1258-THAQ)] can interact with various additives [e.g., iodonium salt, tertiary amine, N-vinylcarbazole, and 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine] under household green LED irradiation to generate active species (cations and radicals). The relevant photochemical mechanism is investigated using quantum chemistry, fluorescence, cyclic voltammetry, laser flash photolysis, steady state photolysis, and electron spin resonance spin-trapping techniques. Furthermore, the multihydroxy-anthraquinone derivative-based photoinitiating systems are capable of initiating cationic photopolymerization of epoxides or divinyl ethers under green LED, and the relevant photoinitiation ability is consistent with the photochemical reactivity (i.e., 124-THAQ-based photoinitiating system exhibits highest reactivity and photoinitiation ability). More interestingly, multihydroxy-anthraquinone derivative-based photoinitiating systems can initiate free radical crosslinking or controlled (i.e., reversible addition-fragmentation chain transfer) photopolymerization of methacrylates under green LED. It reveals that multihydroxy-anthraquinone derivatives can be used as versatile photoinitiators for various types of photopolymerization reactions.

Naphthalimide‐Tertiary Amine Derivatives as Blue‐Light‐Sensitive Photoinitiators

AbstractThe photochemical mechanism of the radical generation from photoinitiating systems based on 1, 8‐naphthalimide derivatives (ANDs; with tertiary amine moieties) are investigated by using various approaches including cyclic voltammetry, steady‐state photolysis, and electron spin resonance spin‐trapping techniques. It reveals that radicals can be produced from ANDs alone or ANDs/additive (e. g. iodonium salt or chloro triazine) combinations. The generated radicals and cations can initiate both free‐radical and cationic photopolymerization reactions under irradiation with various light‐emitting diodes or a halogen lamp. For most of the AND‐based photoinitiating systems, more than 60 % of acrylate or epoxide conversions were attained, and were even higher than those obtained by using commercial photoinitiators, for example, bisacylphosphine oxide or camphorquinone. More interestingly, the AND1‐based photoinitiating system can also initiate concomitant cationic/radical polymerizations and can be used for the synthesis of interpenetrated polymer networks.

Humidity Induces Changes in the Dimensions of Hydrogel-Coated Wool Yarns.

Polymeric hydrogel based on acrylic acid (AA) and N,N-dimethylacrylamide (DMAA) was prepared by photopolymerization reaction, using nano-alumina as the inorganic crosslinker. Hydrogel-coated wool yarns determine their dimensional changes under humidity conditions. Surface morphology of the hydrogel-coated wool yarns was carried out using SEM microscopy. The hydrogel was further characterized by Fourier transformer infrared spectrum (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG). This contribution showed that UV-initiated polymerization coating wool yarns can change the functional properties of wool fibers.