Photopolymerization reactions using the photoinitiated copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction

Development of Essential Oil Delivery Systems by 'Click Chemistry' Methods: Possible Ways to Manage Duchenne Muscular Dystrophy

Recently, rare diseases have received attention due to the need for improvement in diagnosed patients' and their families' lives. Duchenne muscular dystrophy (DMD) is a rare, severe, progressive, muscle-wasting disease. Today, the therapeutic standard for treating DMD is corticosteroids, which cause serious adverse side effects. Nutraceuticals, e.g., herbal extracts or essential oils (EOs), are possible active substances to develop new drug delivery systems to improve DMD patients' lives. New drug delivery systems lead to new drug effects, improved safety and accuracy, and new therapies for rare diseases. Herbal extracts and EOs combined with click chemistry can lead to the development of safer treatments for DMD. In this review, we focus on the need for novel drug delivery systems using EOs as the therapy for DMD and the potential use of click chemistry for drug delivery systems. New EO complex drug delivery systems may offer a new approach for improving muscle conditions and mental health issues associated with DMD. However, further research should identify the potential of these systems in the context of DMD. In this review, we discuss possibilities for applying EOs to DMD before implementing expensive research in a theoretical way.

Copper II Complexes Based on Benzimidazole Ligands as a Novel Photoredox Catalysis for Free Radical Polymerization Embedded Gold and Silver Nanoparticles

The copper II complex's novel benzimidazole Schiff base ligands were manufactured and gauged as a new photoredox catalyst/photoinitiator amalgamated with triethylamine (TEA) and iodonium salt (Iod) for the polymerization of ethylene glycol diacrylate while exposed to visible light by an LED Lamp at 405 nm with an intensity of 543 mW/cm² at 28 °C. Gold and silver nanoparticles were obtained through the reactivity of the copper II complexes with amine/Iod salt. The size of NPs was around 1-30 nm. Lastly, the high performance of copper II complexes for photopolymerization containing nanoparticles is presented and examined. Ultimately, the photochemical mechanisms were observed using cyclic voltammetry. The preparation of the polymer nanocomposite nanoparticles in situ was photogenerated during the irradiation LED at 405 nm with an intensity of 543 mW/cm² at 28 °C process. UV-Vis, FTIR, and TEM analyses were utilized for the determination of the generation of AuNPs and AgNPs which resided within the polymer matrix.

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation

The development of long-wavelength photoinduced copper-catalyzed azide-alkyne click (CuAAC) reaction routes is attractive for organic and polymer chemistry. In this study, we present a novel synthetic methodology for the photoinduced CuAAC reaction utilizing exfoliated two-dimensional (2D) few-layer black phosphorus nanosheets (BPNs) as photocatalysts under white LED and near-IR (NIR) light irradiation. Upon irradiation, BPNs generated excited electrons and holes on its conduction (CB) and valence band (VB), respectively. The excited electrons thus formed were then transferred to the CuII ions to produce active CuI catalysts. The ability of BPNs to initiate the CuAAC reaction was investigated by studying the reaction between various low molar mass alkyne and azide derivatives under both white LED and NIR light irradiation. Due to its deeper penetration of NIR light, the possibility of synthesizing different macromolecular structures such as functional polymers, cross-linked networks and block copolymer has also been demonstrated. The structural and molecular properties of the intermediates and final products were evaluated by spectral and chromatographic analyses.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Light-Activated Stress Relaxation, Toughness Improvement, and Photoinduced Reversal of Physical Aging in Glassy Polymer Networks

A covalent adaptable network (CAN) with high glass transition temperature (T_g ), superior mechanical properties including toughness and ductility, and unprecedented spatio-temporally controlled dynamic behavior is prepared by introducing dynamic moieties capable of reversible addition fragmentation chain transfer (RAFT) into photoinitiated copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based networks. While the CuAAC polymerization yields glassy polymers composed of rigid triazole linkages with enhanced toughness, the RAFT moieties undergo bond exchange leading to stress relaxation upon light exposure. This unprecedented level of stress relaxation in the glassy state leads to numerous desirable attributes including glassy state photoinduced plasticity, toughness improvement during large deformation, and even photoinduced reversal of the effects of physical aging resulting in the rejuvenation of mechanical and thermodynamic properties in physically aged RAFT-CuAAC networks that undergo bond exchange in the glassy state. Surprisingly, when an allyl-sulfide-containing azide monomer (AS-N₃ ) is used to form the network, the network exhibits up to 80% stress relaxation in the glassy state (T_g  - 45 °C) under fixed displacement. In situ activation of RAFT during mechanical loading results in a 50% improvement in elongation to break and 40% improvement in the toughness when compared to the same network without light-activation of RAFT during the tensile testing.

Effects of network structures on the tensile toughness of copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based photopolymers

In the present study, the photo-initiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization was utilized to form structurally diverse glassy polymer networks. Systematic alterations in the monomer backbone rigidity (e.g., cyclic or aliphatic groups with a different length of backbone) and the reactive functional group density (e.g., tetra-, tri-, di-, and mono-functional azide and alkyne monomers) were used to provide readily tailorable network structures with crosslink densities (estimated from the rubbery modulus) varying by a factor of over 20. All eight of the resultant networks exhibited glass transition temperatures (Tg) between 50 and 80 °C with tensile toughness ranging from 28 to 61 MJ m-3. A nearly linear dependence of yield stress and elongation at break (broadly defined as strength and ductility, respectively) on the Tg and rubbery modulus was established in these triazole networks. When a flexible di-alkyne monomer (5 carbon spacing between alkynes) was incorporated in a network composed of a tri-alkyne and di-azide monomer, the elongation at break was improved from 166 to 300 %, while the yield stress was reduced from 36 to 23 MPa. Additionally, the polymer ductility was also varied by incorporating mono-functional azides as chain ends in the network - replacing a sterically hindered stiff mono-azide with a more flexible mono-azide increased the elongation at break from 24 to 185 % and the tensile toughness from 6 to 28 MJ m-3.

Phosphonium Tetraphenylborate: A Photocatalyst for Visible-Light-Induced, Nucleophile-Initiated Thiol-Michael Addition Photopolymerization

A photoinitiation system that utilizes phosphonium tetraphenylborate as the key component was developed for the visible light-triggered nucleophile-catalyzed thiol-Michael addition reaction. This highly reactive catalyst was composed of a photocaged phosphine (methyldiphenylphosphonium tetraphenylborate, MDPP·HBPh₄), a photosensitizer (isopropylthioxanthone, ITX), and a radical scavenger (TEMPO). Unlike the prevailing photobase catalysts, this photoactivatable phosphine system triggers the thiol-Michael addition polymerization by a nucleophile-catalyzed mechanism and provides a controlled stoichiometric reaction between the thiol and the vinyl precursors. This approach enables the formation of homogeneous polymer networks upon low-energy visible light exposure and, thus, broadens its potential applications in bulk polymer materials synthesis and UV-sensitive bioscaffold formation.

Tandem diaza-Cope rearrangement polymerization: turning intramolecular reaction into powerful polymerization to give enantiopure materials for Zn2+ sensors

[3,3]-Sigmatropic rearrangement is a powerful reaction to form C–C bonds stereospecifically; however, owing to intrinsic simultaneous bond formation and breakage, this versatile method has not been utilized in polymerization. Herein, we report a new tandem diaza-Cope rearrangement polymerization (DCRP) that can synthesize polymers with defect-free C–C bond formation from easy and efficient imine formation. A mechanistic investigation by in situ¹H NMR experiments suggests that this polymerization proceeds by a rapid DCR process, forming an enantiospecific C–C bond that occurs almost simultaneously with imine formation. This polymerization produces not only highly stable polymers against hydrolysis due to resonance-assisted hydrogen bonds (RAHBs) but also chiral polymers containing enantiopure salen moieties, which lead to high-performance Zn²⁺-selective turn-on chemosensors with up to 73-fold amplification. We also found that their optical activities and sensing performances are heavily dependent on the reaction temperature, which significantly affects the stereoselectivity of DCR.

Herein, we report a new tandem diaza-Cope rearrangement polymerization synthesizing enantiopure polymers with defect-free C–C bond formation. Furthermore, these polymers can be applied as high-performance turn-on Zn²⁺ sensors.

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes.

The Use of Click-Type Reactions in the Preparation of Thermosets

Click chemistry has emerged as an effective polymerization method to obtain thermosets with enhanced properties for advanced applications. In this article, commonly used click reactions have been reviewed, highlighting their advantages in obtaining homogeneous polymer networks. The basic concepts necessary to understand network formation via click reactions, together with their main characteristics, are explained comprehensively. Some of the advanced applications of thermosets obtained by this methodology are also reviewed.

Near-Infrared Light Dual-Promoted Heterogeneous Copper Nanocatalyst for Highly Efficient Bioorthogonal Chemistry in Vivo

Owing to better stability and biosafety, heterogeneous Cu nanoparticles (CuNPs) have been put forward as a promising candidate to complete the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. However, the inherent poor activity of Cu(0) deterred its wide bioapplication. Herein, we employed near-infrared (NIR) light to dual-promote the CuAAC reaction of a biocompatible heterogeneous copper nanocatalyst through photodynamic and photothermal effects in vitro and in vivo. Specifically, the photodynamic activity could promote the conversion of Cu(0) to Cu(I) to accelerate the catalytic process of CuAAC. The high photothermal conversion efficiency (η = 50.6%) could increase the local temperature, further promoting the whole reaction. Then, a drastically increased reaction rate in a living system ranging from cells to nematodes was achieved in our system. Meanwhile, the better antitumor efficacy has determined with in vivo tumor therapy experiments.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Cleavable coumarin-based oxime esters with terminal heterocyclic moieties: photobleachable initiators for deep photocuring under visible LED light irradiation

Oxime ester photoinitiators with terminal heterocyclic moieties can efficiently initiate acrylate and thiol–ene photopolymerization under 450 nm LED light irradiation to prepare materials of thickness up to 10 mm.

One-component rapid Norrish Type II photoinitiation of bulk photo-CuAAC polymer networks

A one-component photoinitiation scheme was devised utilizing amine-centered trialkyne monomers for the formation of bulk photo-CuAAC polymer networks. The novel monomers maintain rapid polymerization kinetics and allow for tuning of the T_g.

Strategies for Hyaluronic Acid-Based Hydrogel Design in Drug Delivery

Hyaluronic acid (HA) is a natural, linear, endogenous polysaccharide that plays important physiological and biological roles in the human body. Nowadays, among biopolymers, HA is emerging as an appealing starting material for hydrogels design due to its biocompatibility, native biofunctionality, biodegradability, non-immunogenicity, and versatility. Since HA is not able to form gels alone, chemical modifications, covalent crosslinking, and gelling agents are always needed in order to obtain HA-based hydrogels. Therefore, in the last decade, different strategies for the design of physical and chemical HA hydrogels have been developed, such as click chemistry reactions, enzymatic and disulfide crosslinking, supramolecular assembly via inclusion complexation, and so on. HA-based hydrogels turn out to be versatile platforms, ranging from static to smart and stimuli-responsive systems, and for these reasons, they are widely investigated for biomedical applications like drug delivery, tissue engineering, regenerative medicine, cell therapy, and diagnostics. Furthermore, the overexpression of HA receptors on various tumor cells makes these platforms promising drug delivery systems for targeted cancer therapy. The aim of the present review is to highlight and discuss recent advances made in the last years on the design of chemical and physical HA-based hydrogels and their application for biomedical purposes, in particular, drug delivery. Notable attention is given to HA hydrogel-based drug delivery systems for targeted therapy of cancer and osteoarthritis.

Photoinitiated Copper(I) Catalyzed Azide-Alkyne Cycloaddition Reaction for Ion Conductive Networks

The photoinitiated copper(I) catalyzed azide-alkyne cycloaddition (photo-CuAAC) is a 'click' reaction that enables spatially and temporally controlled polymerizations. The solvent-less photopolymerization of multi-functional azide and cationic alkyne monomers results in the rapid formation of a charged polymer network. Full conversion of these monomers is achieved within 30 minutes under mild, blue-light irradiation conditions (470 nm light at 30 mW/cm2). The modulus of the material is readily tuned by controlling the ratio of di- and tri-functional alkyne monomers. Facile exchange of the hydrophobic bistriflimide counterion for a hydroxide anion yields an ion conductive polymer network with photopatternable charged regions. The spatiotemporal nature of the ionic photo-CuAAC reaction coupled with the chemical stability and mechanical flexibility suggests this chemistry is a facile and novel approach for ion-containing material synthesis (e.g., alkaline fuel cells components).

Evaluation of biofilm formation on novel copper-catalyzed azide-alkyne cycloaddition (CuAAC)-based resins for dental restoratives

OBJECTIVE

For the past several decades, the resins used in dental restorations have been plagued with numerous problems, including their implication in biofilm formation and secondary caries. The need for alternative resins is critical, and evaluation of biofilm formation on these resins is essential. The aim of this study was to evaluate in vitro biofilm formation on the surface of novel copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC)-based resins and composites.

METHODS

CuAAC-based resins/composites made from varying azide monomers and different copper concentrations were compared with BisGMA-TEGDMA resins/composites that served as the control. Biofilms were formed using a mono-species model containing a luciferase-expressing strain of Streptococcus mutans. Luciferase activity was measured and the number of viable bacteria was enumerated on biofilms associated with each resin and composite.

RESULTS

A significant reduction (p<0.05) in luciferase activity, and the number of viable bacteria recovered from biofilms on CuAAC-based resins and composites was observed in comparison to biofilms associated with the BisGMA-TEGDMA controls.

SIGNIFICANCE

CuAAC-based resins do still allow for the formation of biofilms; however, the statistically significant reduction of growth that was associated with the CuAAC resin may enhance the longevity of restorations that incorporate CuAAC-based materials.

Copper Ligand and Anion Effects: Controlling the Kinetics of the Photoinitiated Copper(I) Catalyzed Azide-Alkyne Cycloaddition Polymerization

The kinetics of photoinduced copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) polymerizations were assessed as a function of copper(II) amine-based ligands. Copper(II) bromide ligated with 1,1,4,7,10,10-hexamethylenetetramine (HMTETA) exhibited the fastest kinetics in both Norrish type(I) and type(II) photoinitiating systems. A characteristic induction period is observed with these polymerizations and is manipulated by adding an external tertiary amine in Norrish Type(II) photoinitating systems or by changing the anion of the copper(II) salt. Halides, specifically bromide and chloride, exhibit the fastest kinetics with the smallest induction period in comparison with organic anions, such as bistriflimide and triflate. The temporal control of the photo-CuAAC polymerization is affected by pre-ligation of the copper catalyst, by the presence of certain anions such as acetate, and by specific ligands such as tetramethylethylenediamine (TMEDA).

Bismesitoylphosphinic Acid (BAPO-OH): A Ligand for Copper Complexes and Four-Electron Photoreductant for the Preparation of Copper Nanomaterials

Bismesitoylphosphinic acid, (HO)PO(COMes)₂ (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex Cu^II (BAPO-O)₂ (H₂ O)₂ is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from Cu^II into Cu⁰ with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.

Photopolymerized Triazole-Based Glassy Polymer Networks with Superior Tensile Toughness

Photopolymerization is a ubiquitous, indispensable technique widely applied in applications from coatings, inks, and adhesives to thermosetting restorative materials for medical implants, and the fabrication of complex macro-scale, microscale, and nanoscale 3D architectures via additive manufacturing. However, due to the brittleness inherent in the dominant acrylate-based photopolymerized networks, a significant need exists for higher performance resin/oligomer formulations to create tough, defect-free, mechanically ductile, thermally and chemically resistant, high modulus network polymers with rapid photocuring kinetics. This study presents densely cross-linked triazole-based glassy photopolymers capable of achieving preeminent toughness of ≈70 MJ m^-3 and 200% strain at ambient temperature, comparable to conventional tough thermoplastics. Formed either via photoinitiated copper(I)-catalyzed cycloaddition of monomers containing azide and alkyne groups (CuAAC) or via photoinitiated thiol-ene reactions from monomers containing triazole rings, these triazole-containing thermosets completely recover their original dimensions and mechanical behavior after repeated deformations of 50% strain in the glassy state over multiple thermal recovery-strain cycles.

Coumarin-Based Oxime Esters: Photobleachable and Versatile Unimolecular Initiators for Acrylate and Thiol-Based Click Photopolymerization under Visible Light-Emitting Diode Light Irradiation

Developing efficient unimolecular visible light-emitting diode (LED) light photoinitiators (PIs) with photobleaching capability, which are essential for various biomedical applications and photopolymerization of thick materials, remains a great challenge. Herein, we demonstrate the synthesis of a series of novel PIs, containing coumarin moieties as chromophores and oxime ester groups as initiation functionalities and explore their structure-activity relationship. The investigated oxime esters can effectively induce acrylates and thiol-based click photopolymerization under 450 nm visible LED light irradiation. The initiator O-3 exhibited excellent photobleaching capability and enabled photopolymerization of thick materials (∼4.8 mm). The efficient unimolecular photobleachable initiators show great potential in dental materials and 3D printings.

Progress on Catalytic Systems Used in Click Polymerization

Click polymerization, a powerful synthetic technique to construct polymers with unique structures and advanced functions, is of crucial importance in the areas of polymer and material sciences. A variety of click polymerizations such as azide-alkyne, thiol-yne, amino-yne, and hydroxyl-yne reactions have been established, wherein the catalytic systems play an indispensable role in realizing these highly practical reactions based on triple-bond building blocks, as they directly influence the efficiencies of the click polymerizations and the performances of the resultant polymers. The vital employment of catalysts is reviewed and their developments from innovative discoveries to the eminent position are outlined. Moreover, the challenges and perspectives in this area are also briefly discussed.

Interface Engineering via Photopolymerization-Induced Phase Separation for Flexible UV-Responsive Phototransistors

Interface engineering has been recognized to be substantially critical for achieving efficient charge separation, charge carrier transport, and enhanced device performance in emerging optoelectronics. Nevertheless, precise control of the interface structure using current techniques remains a formidable challenge. Herein, we demonstrate a facile and versatile protocol wherein in situ thiol-ene click photopolymerization-induced phase separation is implemented for constructing heterojunction semiconductor interfaces. This approach generates continuous mountainlike heterojunction interfaces that favor efficient exciton dissociation at the interface while providing a continuous conductive area for hole transport above the interface. This facile low-temperature paradigm presents good adaptability to both rigid and flexible substrates, offering high-performance UV-responsive phototransistors with a normalized detectivity up to 6.3 × 10¹⁴ cm Hz^1/2 W^-1 (also called jones). Control experiments based on ex situ photopolymerization and in situ thermal polymerization are also implemented to demonstrate the superiority of this novel paradigm.

Blue-light activated rapid polymerization for defect-free bulk Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) crosslinked networks

A visible-light (470 nm wavelength) sensitive Type II photoinitiator system is developed for bulk Cu(i)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions in crosslinked networks. The accelerated photopolymerization eliminates UV-mediated azide decomposition allowing for the formation of defect-free glassy networks which exhibit a narrow glass transition temperature.

Photocatalysis in organic and polymer synthesis

This review, with over 600 references, summarizes the recent applications of photoredox catalysis for organic transformation and polymer synthesis. Photoredox catalysts are metallo- or organo-compounds capable of absorbing visible light, resulting in an excited state species. This excited state species can donate or accept an electron from other substrates to mediate redox reactions at ambient temperature with high atom efficiency. These catalysts have been successfully implemented for the discovery of novel organic reactions and synthesis of added-value chemicals with an excellent control of selectivity and stereo-regularity. More recently, such catalysts have been implemented by polymer chemists to post-modify polymers in high yields, as well as to effectively catalyze reversible deactivation radical polymerizations and living polymerizations. These catalysts create new approaches for advanced organic transformation and polymer synthesis. The objective of this review is to give an overview of this emerging field to organic and polymer chemists as well as materials scientists.

Recent advances in alkyne-based click polymerizations

The recent progress in alkyne-based click polymerizations and their application in the preparation of new functional polymers are summarized. The challenges and opportunities in this area are also briefly discussed.

A pH-responsive polymer based on dynamic imine bonds as a drug delivery material with pseudo target release behavior

In this study, pentaerythritol tetra(3-mercaptopropionate)-allylurea-poly(ethylene glycol) (PETMP-AU-PEG), produced by the Schiff-base reaction between terminal-aldehyded PEG and PETMP-AU, was used to prepare doxorubicin (DOX)-loaded polymers for triggered release.

N-[2-(Dimethylamino)ethyl]-1,8-naphthalimide derivatives as photoinitiators under LEDs

Four N-[2-(dimethylamino)ethyl]-1,8-naphthalimide derivatives (ANNs) with different substituents in the naphthalimide skeleton have been synthesized and can be used as versatile photoinitiators under various LEDs.

Fully recoverable rigid shape memory foam based on copper-catalyzed azide-alkyne cycloaddition (CuAAC) using a salt leaching technique

This study is the first to employ the use of the copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization to form a tough and stiff, porous material from a well-defined network possessing a high glass transition temperature. The effect of the network linkages formed as a product of the CuAAC reaction, i.e., the triazoles, on the mechanical behavior at high strain was evaluated by comparing the CuAAC foam to an epoxy-amine-based foam, which consisted of monomers with similar backbone structures and mechanical properties (i.e., T_g of 115 °C and a rubbery modulus of 1.0 MPa for the CuAAC foam, T_g of 125 °C and a rubbery modulus of 1.2 MPa for the epoxy-amine foam). When each foam was compressed uniformly to 80% strain at ambient temperature, the epoxy-amine foam was severely damaged after only reaching 70% strain in the first compression cycle with a toughness of 300 MJ/m³. In contrast, the CuAAC foam exhibited pronounced ductile behavior in the glassy state with three times higher toughness of 850 MJ/m³ after the first cycle of compression to 80% strain. Additionally, when the CuAAC foam was heated above T_g after each of five compression cycles to 80% strain at ambient temperature, the foam completely recovered its original shape while exhibiting a gradual decrease in mechanical performance over the multiple compression cycles. The foam demonstrated almost complete shape fixity and recovery ratios even through five successive cycles, indicative of "reversible plasticity", making it highly desirable as a glassy shape memory foams.

Kinetics and mechanics of photo-polymerized triazole-containing thermosetting composites via the copper(I)-catalyzed azide-alkyne cycloaddition

OBJECTIVE

Several features necessary for polymer composite materials in practical applications such as dental restorative materials were investigated in photo-curable CuAAC (copper(I)-catalyzed azide-alkyne cycloaddition) thermosetting resin-based composites with varying filler loadings and compared to a conventional BisGMA/TEGDMA based composite.

METHODS

Tri-functional alkyne and di-functional azide monomers were synthesized for CuAAC resins and incorporated with alkyne-functionalized glass microfillers for CuAAC composites. Polymerization kinetics, in situ temperature change, and shrinkage stress were monitored simultaneously with a tensometer coupled with FTIR spectroscopy and a data-logging thermocouple. The glass transition temperature was analyzed by dynamic mechanical analysis. Flexural modulus/strength and flexural toughness were characterized in three-point bending on a universal testing machine.

RESULTS

The photo-CuAAC polymerization of composites containing between 0 and 60wt% microfiller achieved ∼99% conversion with a dramatic reduction in the maximum heat of reaction (∼20°C decrease) for the 60wt% filled CuAAC composites as compared with the unfilled CuAAC resin. CuAAC composites with 60wt% microfiller generated more than twice lower shrinkage stress of 0.43±0.01MPa, equivalent flexural modulus of 6.1±0.7GPa, equivalent flexural strength of 107±9MPa, and more than 10 times higher energy absorption of 10±1MJm-3 when strained to 11% relative to BisGMA-based composites at equivalent filler loadings.

SIGNIFICANCE

Mechanically robust and highly tough, photo-polymerized CuAAC composites with reduced shrinkage stress and a modest reaction exotherm were generated and resulted in essentially complete conversion.