Photoinitiated Radical Polymerization Research Articles

Methacrylate-Containing <i>n</i>-Derivatives of <i>N</i>,<i>N</i>-Diethyl-4-(Phenyldiazenyl)Aniline as Initiators in Two-Photon Polymerization

The possibility of using a number of methacrylate-containing N,N-diethyl-4-(phenyldiazenyl)anilines with various para-substituents with respect to the azo group (-H, -Br, -NO2) as photoinitiators of radical polymerization is considered. The electrochemical and photoluminescent properties of these compounds have been studied. In the presence of azo dyes, two-photon photopolymerization of pentaerythritol triacrylate was carried out by focused radiation from a femtosecond laser with a wavelength of 780 nm. Structures with minimum linear element sizes of 94 ± 5 nm were obtained by DLW nanolithography, as well as 3D microstructures of complex architecture.

Rapid synthesis of solid polycarboxylate superplasticizers via photoinitiated radical polymerization

The synthesis and performance optimization of solid polycarboxylate superplasticizers (PCEs) present significant challenges. In our study, a rapid synthesis of a solid polycarboxylate superplasticizer (IPCE10) was achieved using photoinitiated free radical polymerization. IPCE10 exhibited good dispersibility and improved compressive strength in concrete. Dynamic light scattering tests and molecular dynamics simulations demonstrated that the adsorption conformation of IPCE10 on the calcium silicate hydrate surface was relatively dispersed, with a thicker adsorption layer. This indicates that IPCE10 has stronger steric hindrance, resulting in superior dispersibility. Additionally, density functional theory calculations of the reaction energy barriers for radical generation by photoinitiated and azo-initiated monomers revealed that the energy barrier in the photoinitiated system was significantly lower than that in the azo-initiated system, indicating that photoinitiated polymerization is more feasible. This study proposes a simple and rapid method for the preparation of solid polycarboxylate superplasticizers, providing valuable insights for the development of high-value-added construction materials.

POSS based poly (zwitterionic liquids) electrolytes with 3D crosslinked networks for lithium metal batteries

Polymer electrolyte is a potential candidate for the next-generation lithium metal batteries. However, its low room temperature ionic conductivity limited its practical application. Here, a novel POSS-based poly (zwitterionic liquids) organic–inorganic hybrid electrolyte with 3D crosslinked networks was proposed for enabling lithium-ion fast transport by photoinitiated radical polymerization of vinyl zwitterionic monomers and acrylate monomers containing rich EO units and POSS. The synergistic effect of unique structures of 3D organic–inorganic hybrids gel electrolytes such as zwitterionic, rich EO segments and POSS cages facilitate Li+ conduction, resulting in high room temperature ionic conductivity (1.03 × 10-3 S cm-1) and a satisfactory Li+ transference number (0.45). The lithium-symmetric batteries assembled with the novel POSS-based poly (zwitterionic liquids) gel hybrid electrolytes can operate continuously at 0.1 mA cm-2 for 2300 h without any obvious short circuit, indicating good interfacial compatibility between the electrolytes and lithium electrodes. The Li/LiFePO4 batteries assembled with the novel POSS-based poly (zwitterionic liquids) gel hybrid electrolytes exhibit long-term stability.

Cyclo‐Bis(Acyl)phosphine Oxides as Efficient Photoinitiators for Radical Polymerization

AbstractAcyclic acylphosphine oxides have been extensively utilized in industrial applications as typical photoinitiators (PIs). In this study, we demonstrate the efficiency of their cyclic analogues, cyclo‐bis(acyl)phosphine oxides (CBAPOs), as efficient PIs. We present the isolation and X‐ray crystallographic characterization of CBAPOs. These compounds exhibit a long maximum absorption wavelength ranging between 415 and 420 nm, extending well into the near 500 nm region. Radical trapping experiments suggest that CBAPOs undergo homolytic P−C(O) bond α‐cleavage. Steady‐state photolysis conducted with LED light at 390 nm, monitored by UV‐Vis spectroscopy, confirms the gradual decay of CBAPOs over time. Additionally, all CBAPOs are capable of initiating radical polymerization under irradiation at 365 nm. Notably, one of the CBAPOs (4a) demonstrates comparable photoinitiating efficiency to one of commercially available bis(acyl)phosphine oxides (Irgacure 819).

Bionic double-crosslinked hydrogel of poly (γ-glutamic acid)/poly (N-(2-hydroxyethyl) acrylamide) with ultrafast gelling process and ultrahigh burst pressure for emergency rescue

Injectable adhesive hydrogels combining rapid gelling with robust adhesion to wet tissues are highly required for fast hemostasis in surgical and major trauma scenarios. Inspired by the cross-linking mechanism of mussel adhesion proteins, we developed a bionic double-crosslinked (BDC) hydrogel of poly (γ-glutamic acid) (PGA)/poly (N-(2-hydroxyethyl) acrylamide) (PHEA) fabricated through a combination of photo-initiated radical polymerization and hydrogen bonding cross-linking. The BDC hydrogel exhibited an ultrafast gelling process within 1 s. Its maximum adhesion strength to wet porcine skin reached 254.5 kPa (9 times higher than that of cyanoacrylate (CA) glue) and could withstand an ultrahigh burst pressure of 626.4 mmHg (24 times higher than that of CA glue). Notably, the BDC hydrogel could stop bleeding within 10 s from a rat liver incision 10 mm long and 5 mm deep. The wound treated with the BDC hydrogel healed faster than the control groups, underlining the potential for emergency rescue and wound care scenarios.

Synthesis of Polycarboxylate Superplasticizers via Photoinitiated Radical Polymerization

Synthesis of Polycarboxylate Superplasticizers via Photoinitiated Radical Polymerization

Porous hydrogel microspheres with excellent temperature-sensitive, magnetic and fluorescent properties for drug delivery.

Porous hydrogel microspheres with temperature-sensitive, magnetic and fluorescent properties have great potential for drug delivery. In this study, porous hydrogel microspheres with excellent temperature-sensitive, magnetic and fluorescent properties were prepared through droplet microfluidics and photoinitiated radical polymerization, which were characterized via scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), fluorescence spectroscopy, ultraviolet spectrophotometry, and other techniques. The volumetric phase-transition temperature of porous hydrogel microspheres was in the range of 40-45 °C, and the volume swelling ratio reached 5.26 as the temperature decreased from 55 °C to 25 °C. Meanwhile, the saturation magnetization and optimal fluorescence emission wavelength of porous hydrogel microspheres were 1.79 emu g-1 and 616 nm, respectively, which can be an effective strategy to visually monitor and control the speed of drug release during magnetic heat therapy. Finally, bovine serum albumin (BSA) was employed as a model drug to investigate the drug loading and release of porous hydrogel microspheres. The maximal drug loading amount was 238 mg g-1, and the drug release speed and amount can be correspondingly promoted by altering the temperature.

Inducing an LCST in hydrophilic polysaccharides via engineered macromolecular hydrophobicity

Thermoresponsive polysaccharide-based materials with tunable transition temperatures regulating phase-separated microdomains offer substantial opportunities in tissue engineering and biomedical applications. To develop novel synthetic thermoresponsive polysaccharides, we employed versatile chemical routes to attach hydrophobic adducts to the backbone of hydrophilic dextran and gradually increased the hydrophobicity of the dextran chains to engineer phase separation. Conjugating methacrylate moieties to the dextran backbone yielded a continuous increase in macromolecular hydrophobicity that induced a reversible phase transition whose lower critical solution temperature can be modulated via variations in polysaccharide concentration, molecular weight, degree of methacrylation, ionic strength, surfactant, urea and Hofmeister salts. The phase separation is driven by increased hydrophobic interactions of methacrylate residues, where the addition of surfactant and urea disassociates hydrophobic interactions and eliminates phase transition. Morphological characterization of phase-separated dextran solutions via scanning electron and flow imaging microscopy revealed the formation of microdomains upon phase transition. These novel thermoresponsive dextrans exhibited promising cytocompatibility in cell culture where the phase transition exerted negligible effects on the attachment, spreading and proliferation of human dermal fibroblasts. Leveraging the conjugated methacrylate groups, we employed photo-initiated radical polymerization to generate phase-separated hydrogels with distinct microdomains. Our bottom-up approach to engineering macromolecular hydrophobicity of conventional hydrophilic, non-phase separating dextrans to induce robust phase transition and generate thermoresponsive phase-separated biomaterials will find applications in mechanobiology, tissue repair and regenerative medicine.

Grafting α-aminoketone to SMA via highly efficient amide bond and their performances as macrophotoinitiators

Water-soluble macrophotoinitiators that can realize a high photoactivity together with low migration in waterborne photopolymerization systems are very necessary. However, the precise, highly efficient preparation of macrophotoinitiators remains a substantial challenge, such as grafting side chains according to stoichiometric ratios. Herein, based on styrene maleic anhydride copolymer (SMA) prepared by photopolymerization, water soluble macrophotoinitiators SMA5k-Ns and SMA13k-Ns series with controllable structure were successfully prepared through the amino bond of α-aminoketone small-molecule photoinitiator with maleic anhydride moieties. All of them exhibited excellent water dispersion properties, and solution photopolymerizations investigation showed they can be used as photoinitiators for radical polymerization with high conversion (up to 95%) in waterborne systems under LED@365–405 nm. Furthermore, the migration stabilities of these photoinitiators in photocured hydrogels were better than those of commercial photoinitiators. High efficiency and low migration make them have great potential applications in food packaging and biological materials.

New Photocrosslinked 3D Foamed Scaffolds Based on GelMA Copolymers: Potential Application in Bone Tissue Engineering.

The production of customized polymeric hydrogels in the form of 3D scaffolds with application in bone tissue engineering is currently a topic of great interest. Based on gelatin methacryloyl (GelMa) as one of the most popular used biomaterials, GelMa with two different methacryloylation degrees (DM) was obtained, to achieve crosslinked polymer networks by photoinitiated radical polymerization. In this work, we present the obtention of new 3D foamed scaffolds based on ternary copolymers of GelMa with vinylpyrrolidone (VP) and 2-hydroxyethylmethacrylate (HEMA). All biopolymers obtained in this work were characterized by infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), whose results confirm the presence of all copolymers in the crosslinked biomaterial. In addition, scanning electron microscopy (SEM) pictures were obtained verifying the presence of the porosity created by freeze-drying process. In addition, the variation in its swelling degree and its enzymatic degradation in vitro was analyzed as a function of the different copolymers obtained. This has allowed us to observe good control of the variation in these properties described above in a simple way by varying the composition of the different comonomers used. Finally, with these concepts in mind, biopolymers obtained were tested through assessment of several biological parameters such as cell viability and differentiation with MC3T3-E1 pre-osteoblastic cell line. Results obtained show that these biopolymers maintain good results in terms of cell viability and differentiation, along with tunable properties in terms of hydrophilic character, mechanical properties and enzymatic degradation.

Latest Advances in Highly Efficient Dye-Based Photoinitiating Systems for Radical Polymerization.

Light-activated polymerization is one of the most important and powerful strategies for fabrication of various types of advanced polymer materials. Because of many advantages, such as economy, efficiency, energy saving and being environmentally friendly, etc., photopolymerization is commonly used in different fields of science and technology. Generally, the initiation of polymerization reactions requires not only light energy but also the presence of a suitable photoinitiator (PI) in the photocurable composition. In recent years, dye-based photoinitiating systems have revolutionized and conquered the global market of innovative PIs. Since then, numerous photoinitiators for radical polymerization containing different organic dyes as light absorbers have been proposed. However, despite the large number of initiators designed, this topic is still relevant today. The interest towards dye-based photoinitiating systems continues to gain in importance, which is related to the need for new initiators capable of effectively initiating chain reactions under mild conditions. In this paper we present the most important information about photoinitiated radical polymerization. We describe the main directions for the application of this technique in various areas. Attention is mainly focused on the review of high-performance radical photoinitiators containing different sensitizers. Moreover, we present our latest achievements in the field of modern dye-based photoinitiating systems for the radical polymerization of acrylates.

Nanofibers as precursors for the rapid formation of hydrogels.

Hydrogels can be used in surgeries, which require a support material to maintain the correct anatomy. One major limitation is however the time required for the preparation of hydrogels under urgent conditions. Herein, we report a new method for a very fast preparation of hydrogels at room temperature. Nanofibers of dextran containing vinyl groups produced by electrospinning are loaded with redox- or photo-initiators for radical polymerization. Once dissolved in water, the nanofibers yield hydrogels either spontaneously or upon irradiation with UV light. We also show that the nanofibers can be loaded with active fillers so that hydrogels embedding nanocapsules are obtained. This concept could be applied for the rapid preparation of functional hydrogels which are needed as implants.

A road map on synthetic strategies and applications of biodegradable polymers.

Biodegradable polymers have emerged as fascinating materials due to their non-toxicity, environmentally benign nature and good mechanical strength. The toxic effects of non-biodegradable plastics paved way for the development of sustainable and biodegradable polymers. The engineering of biodegradable polymers employing various strategies like radical ring opening polymerization, enzymatic ring opening polymerization, anionic ring opening polymerization, photo-initiated radical polymerization, chemoenzymatic method, enzymatic polymerization, ring opening polymerization and coordinative ring opening polymerization have been discussed in this review. The application of biodegradable polymeric nanoparticles in the biomedical field and cosmetic industry is considered to be an emerging field of interest. However, this review mainly highlights the applications of selected biodegradable polymers like polylactic acid, poly(ε-caprolactone), polyethylene glycol, polyhydroxyalkanoates, poly(lactide-co-glycolide) and polytrimethyl carbonate in various fields like agriculture, biomedical, biosensing, food packaging, automobiles, wastewater treatment, textile and hygiene, cosmetics and electronic devices.

Organocatalyzed Phospha-Michael Addition: A Highly Efficient Synthesis of Customized Bis(acyl)phosphane Oxide Photoinitiators.

Addition of the P-H bond in bis(mesitoyl)phosphine, HP(COMes)2 (BAPH), to a wide variety of activated carbon-carbon double bonds as acceptors was investigated. While this phospha-Michael addition does not proceed in the absence of an additive or catalyst, excellent results were obtained with stoichiometric basic potassium or caesium salts. Simple amine bases can be employed in catalytic amounts, and tetramethylguanidine (TMG) in particular is an outstanding catalyst that allows the preparation of bis(acyl)phosphines, R-P(COMes)2 , under very mild conditions in excellent yields after only a short time. All phosphines RP(COMes)2 can subsequently be oxidized to the corresponding bis(acyl)phosphane oxides, RPO(COMes)2 , a substance class belonging to the most potent photoinitiators for radical polymerizations known to date. Thus, a simple and highly atom economic method has been found that allows the preparation of a broad range of photoinitiators adapted to their specific field of application even on a large scale.

Experimental study on mechanism of stable drag reduction with hydrogel interface

The hydrogel is a novel material with drag-reducing ability, which has great potential to be applied in marine applications. In this paper, a series of superhydrophilic hydrogels were prepared by photoinitiated radical polymerization. The Couette flow and particle image velocimeter (PIV) observation in the water tunnel were conducted to investigate the drag-reducing characteristics of the prepared hydrogels. The results show that the hydrogel thickness of 1500 µm is the critical value corresponding to the maximum drag reduction rate of about 68%. The drag reduction is induced by the boundary slip phenomenon on the hydrophilic surface, and the further mechanism can be explained in two aspects. On one hand, the generated vorticities in the grooves between the macroscopic convex structures of the hydrogel induce the fluid sliding state converted into the rolling state. This state transformation reduces the near-wall velocity gradient, and thus promotes the generation of boundary slip. On the other hand, fluorescence particle experiments reveal that there exists water exchange between the inside and outside of the hydrogel. This exchange would promote the relative velocity, and thus strengthens the boundary slip. The present work is expected to make a certain contribution to reveal the drag reduction mechanism of hydrogel.

Large-molecular-weight acyldiphenylphosphine oxides as low-mobility type I photoinitiator for radical polymerization

In recent years, the light source for photopolymerization technology is evolving from energy-hungry mercury lamps to the safer light-emitting diodes (LEDs), and it is urgent to develop new photoinitiator adapted to the photopolymerization system with LED light source. Some acyldiphenylphosphine oxide photoinitiators have been designed and developed for LED light source, but their application is severely limited in the fields of food packing, medical equipment, environmentally-friendly product etc. due to their high mobility in photocured polymers. In this study, eight acyldiphenylphosphine oxide molecules (DAPO-1 ∼ DAPO-8) were synthesized by introducing large molecular weight groups and their UV–visible absorption, photodegradation quantum yield, photopolymerization properties, mobility and solubility in monomer were determined. Thereinto, photoinitiators show lower mobility than TPO, the photoinitiator commonly used in industry, as well as good solubility in monomers and excellent photopolymerization performance. Therefore, they can serve as potential substitutes for commercial TPO, especially in the application of low-migration photocurable system.

Superior, Environmentally Tolerant, Flexible, and Adhesive Poly(ionic liquid) Gel as a Multifaceted Underwater Sensor.

In recent years, gel-based sensors have been widely considered and fully developed. However, it is of vital importance, yet rather challenging to achieve a multifaceted gel, which can unify the advantages of favorable conductivity, high adhesion, excellent environmental resistance, and so forth and be applied in various harsh conditions. Herein, an ideal, extremely stable, adhesive, conductive poly(ionic liquid) gel (PILG) was designed via a one-step photoinitiated radical polymerization based on 1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (VBIm-NTf2) cross-linked with ethylene glycol dimethacrylate (EGDMA) in methyltributylammonium bis(trifluoromethanesulfonyl)imide (N1444-NTf2) medium. There are abundant hydrophobic butyl chains and fluorinated groups in VBIm-NTf2 and N1444-NTf2, which can impart the PILG with stable conductivity, excellent environmental tolerance, and adhesion even in water due to the ion-dipole and ion-ion interactions. The resulting PILG can be assembled as a soft and smart sensor that can be applied in specific conditions such as underwater or undersea and even in dynamic water, achieving a stable signal transmission. Meanwhile, the PILG can be utilized as a flexible electrode to convey ECG signals in air or water whether it is in the static or dynamic state. Therefore, it is envisioned that this novel PILG will serve as a hopeful electrical device for signal detection and healthy management in specific environments.

Liquid Metal Nanoparticles as a Highly Efficient Photoinitiator to Develop Multifunctional Hydrogel Composites

Liquid metal (LM) composites are a class of emerging soft multifunctional materials that are promising for a variety of applications, yet the chemistry properties of LM have not been fully understood. Here, we report that LM nanoparticles can directly perform as a photoinitiator for radical polymerization and the in situ development of highly tough and multifunctional LM hydrogel composites. It is revealed that the photocatalytic activity of LM nanoparticles originates from the oxide layer on LM. Significantly, positively charged metal-organic framework (MOF) nanoparticles are used to stabilize LM nanoparticles in aqueous solutions, where the MOF can anchor on the surface of LM nanoparticles by electrostatic interaction while helping to preserve the unshielded oxide layer, therefore realizing the highly efficient photoinitiation and polymerization. The LM nanoparticle-initiated photopolymerization is shown to develop hydrogel composites featuring excellent stretchability, stimuli responsiveness, and sustained photocatalytic activity. The photocatalytic polymerization initiated by LM nanoparticles not only deepens the understanding on the semiconductor properties of the oxide skin on LM but also broadens the application scenarios of multifunctional LM/polymer composites in smart materials, wearable electronics, and soft robotics.

New acyl phosphine oxides as high-performance and low migration type I photoinitiators of radical polymerization

Two low migration acylphosphine oxide photoinitiators (APO and DAPO) containing unsaturated CC double bonds have been designed and synthesized for free radical polymerization. The properties and performances of APO and DAPO in the free radical polymerization of trimethylolpropane triacrylate (TMPTA) were evaluated and compared with the commercial photoinitiator 2,4,6-trimethyl(phenyl) diphenyl oxide (TPO). The results show that DAPO exhibited the best double bond conversion (DC) of TMPTA in the photoinitiators tested under the same reaction conditions. The migration ratio of APO and DAPO was 2/3 and 1/3 of that of TPO respectively indicating lower migration than the conventional photoinitiator, and the solubility of DAPO in monomers was close to that of TPO, which provided the possibility for the industrial application of DAPO.

High-Performance UV-Vis Light Induces Radical Photopolymerization Using Novel 2-Aminobenzothiazole-Based Photosensitizers.

The popularity of using the photopolymerization reactions in various areas of science and technique is constantly gaining importance. Light-induced photopolymerization is the basic process for the production of various polymeric materials. The key role in the polymerization reaction is the photoinitiator. The huge demand for radical and cationic initiators results from the dynamic development of the medical sector, and the optoelectronic, paints, coatings, varnishes and adhesives industries. For this reason, we dealt with the subject of designing new, highly-efficient radical photoinitiators. This paper describes novel photoinitiating systems operating in UV-Vis light for radical polymerization of acrylates. The proposed photoinitiators are composed of squaraine (SQ) as a light absorber and various diphenyliodonium (Iod) salts as co-initiators. The kinetic parameters of radical polymerization of trimethylolpropane triacrylate (TMPTA), such as the degree of double bonds conversion (C%), the rate of photopolymerization (Rp), as well as the photoinitiation index (Ip) were calculated. It was found that 2-aminobenzothiazole derivatives in the presence of iodonium salts effectively initiated the polymerization of TMPTA. The rates of polymerization were at about 2 × 10−2 s−1 and the degree of conversion of acrylate groups from 10% to 36% were observed. The values of the photoinitiating indexes for the most optimal initiator concentration, i.e., 5 × 10−3 M were in the range from 1 × 10−3 s−2 even to above 9 × 10−3 s−2. The photoinitiating efficiency of new radical initiators depends on the concentration and chemical structure of used photoinitiator. The role of squaraine-based photoinitiating systems as effective dyeing photoinitiators for radical polymerization is highlighted in this article.