Photoinitiated Polymerization Research Articles

Synthesis and photoinitiated cationic polymerization of epoxy monomers derived from oleic acid comprising one to three epoxy groups

A series of bio-based epoxy compounds based on oleic acid combined with aliphatic or aromatic structures were studied regarding selected properties such as melting behavior and viscosity as well as their reactivity in a photoinitiated cationic polymerization. The new epoxy compounds derived from oleic acid and either eugenol or isoeugenol, epoxidized triolein, and an epoxy compound derived from oleic acid and popane diol-1,3 contain 100 % renewable carbon. Atom economy differs not only for the esterification and epoxidation reaction, also selection of hydrogen peroxide or m-chloroperbenzoic acid for the epoxidation significantly influences the atom economy of this reaction step. Variation of the chemical structure of the bio-based epoxy compounds derived from oleic acid and either an aliphatic alcohol or a phenolic compound results in differences in both melting behavior and viscosity of the epoxy monomers that is important for the photoinitiated cationic polymerization. Kinetic investigation of the photoinitiated cationic polymerization of the bio-based epoxy compounds using photo-DSC shows significant differences in the polymerization rate and conversion as a function of the irradiation time for the epoxy monomers. RT-FTIR spectroscopy gives additional information about the polymerization kinetics for epoxy monomers that are liquid at room temperature. The glass transition temperature of the photopolymers analyzed by DSC is mostly below room temperature that is attributed to the high content of flexible structures containing in the polymers. Additional investigation of the soluble photopolymers by GPC resulted in a molecular weight corresponding to the oligomer region and a dispersity higher than one. The bio-based epoxy monomers comprising two or three epoxy groups may be interesting for application, e. g. in coatings or adhesives, because photoinitiated polymerization results in crosslinking. Epoxy compounds containing only one epoxy group may be useful for viscosity reduction of the photopolymerizing mixtures because of their lower viscosity compared to the epoxy monomers comprising more than one epoxy group.

Photo‐controllable cationic homopolymerization and random copolymerization of vinyl ethers based on iridium salt photocatalyst

AbstractTemporal control of chain growth is a central challenge for photoinitiated active polymerization. In this work, we introduced an iridium salt complex‐based catalyst system to achieve fine temporal control of the chain growth process. By electrochemical analysis, compared with the pyran salt photocatalyst, it was found that the iridium salt complex could promote the chain transfer of active species to reversible addition‐fragmentation chain transfer polymerization (RAFT) reagent, thereby generating dormant species, which provided the possibility of time control of the polymerization process. Using this catalytic system, we successfully achieved homopolymerization of vinyl ethers with different substituents and random copolymerization with isobutyl vinyl ethers, which is not only pointed the way for broadening the monomer selection in the future, but also provided an innovative way to prepare new functionalized materials.

Photoredox dual catalysis using stimulus-responsive fluoresceins for colorimetric detection of Hg(II) ions

We demonstrate photoredox dual catalysis using fluorescein derivatives and apply it to polymerization-based signal amplification (PBA) under the irradiation of visible light. The mechanism of the photoredox dual catalysis is elucidated using electron paramagnetic resonance (EPR) and UV–Vis spectroscopies. We applied the photoredox dual catalysis to amplify and readout the signal of Hg(II) ions with the unaided eye through photoinitiated free-radical polymerization. Although PBA offers a reliable and rapid colorimetric method for analyte detection, its sensitivity remains a challenge compared with fluorescence detection. To address this issue, we designed a dual system involving activatable fluoresceins that selectively react to external stimuli, followed by their action as photoredox catalysts/initiators. As a proof-of-concept, we employed fluorescin and eosin hydrazide (EYHZ) as light- and Hg(II) ion-responsive probes, respectively. This dual system selectively initiated the polymerization of poly(ethylene glycol) diacrylate (PEGDA) in the presence of Hg(II) ions under visible light. Remarkably, this photoredox dual catalysis approach allowed the unaided eye to detect of Hg(II) ions as low as 90 nM in aqueous solution, demonstrating its potential for sensitive and versatile sensing applications.

Visible light radical photoinitiators of polymerization based on photochromic molecules

A series of photochromic compounds linked to a benzophenone nucleus were synthetized and evaluated regarding their ability to act as Norrish type II radical photoinitiators, promoting the polymerization of a polyacrylate monomer after the consecutive absorption of LED UV and Vis light.

Synthesis and photo‐initiated radical polymerization of methacrylates derived from bio‐based ω‐hydroxycarboxylic acids

AbstractThe bio‐based methacrylates 9‐(methacryloyloxy)‐10,18‐dihydroxyoctadecanoic acid/9,18‐dihydroxy‐10‐(methacryloyloxy)octadecanoic acid isomer mixture and 22‐methacryloyloxydocosanoic acid were synthesized from 9,10‐epoxy‐18‐hydroxyoctadecanoic acid and 22‐hydroxydocosanoic acid. The white crystalline 9,10‐epoxy‐18‐hydroxyoctadecanoic acid and cream‐colored 22‐hydroxydocosanoic acid were isolated from both the bark of Betula pendula and cork of Quercus suber after extraction of the milled plant materials with methanol, treating the insoluble residues with 2‐propanole containing suspended sodium hydroxide, application of a working up procedure developed in this work for the resulting mixture, and purification of the products obtained. The new bio‐based methacrylates show higher reactivity in the photoinitiated polymerization in comparison with the commercial laurylmethacrylate as detected by photo‐differential scanning calorimetry (DSC). For comparison, traditional free radical polymerization of the new bio‐based methacrylates was carried out in dimethylsulfoxide using 2,2'‐azobis‐(2‐propionitrile) as initiator. Furthermore, the quantitative conversion of the bio‐based monomers during the photoinitiated polymerization makes these bio‐based monomers interesting for application in coatings. As expected, the photopolymer made from the 9‐(methacryloyloxy)‐10,18‐dihydroxyoctadecanoic acid/9,18‐dihydroxy‐10‐(methacryloyloxy)octadecanoic acid isomer mixture is amorphous. Interestingly, the photopolymer made from the 22‐methacryloyloxydocosanoic acid contains crystalline structures as detected by DSC investigation.

Rational design of biomass-derived and UV-curable dynamic polymer for the encapsulation of paper-based flexible strain sensor

The paper-based flexible electronic devices with the virtues of light weight, porousness, sustainability and low cost by paper-making technology, however its application may be restricted by the poor tolerance of water due to the abundance of hydroxyl group of cellulose fibers. The encapsulation of such device requires to keep its sustainability and match the high efficiency of paper-making industry. In this work, a series of biomass-derived and UV-curable dynamic polymers were synthesized using itaconic acid and binary alcohols as raw materials. The diglycidyl ethers were firstly synthesized through the substitution reaction between binary alcohols and epichlorohydrin. The oligomer was then prepared by ring-opening reactions between the diglycidyl ethers and glycidyl-methacrylate-modified itaconic acid precursor. The dynamic polymers were finally obtained from photo-initiated polymerization, of which the mechanical property was regulated by the length of the binary alcohols. It is found that the polymer from 1,10-decanol possessed the highest tensile strength of 5.8 MPa and biggest elongation at break of 4.1%. The polymer can be self-healed and recycled, and was proved to be used as a photoresist for printed circuit board (PCB). Furthermore, the polymer was successfully applied to encapsulation of paper-based flexible strain sensor, which exhibited hydrophobicity and significantly higher working stability under high humidity or human sweating condition. The strategy reported in this work may pave a way for the development of sustainable thermosetting polymers and sustainable flexible electronic devices with high performance.

Light-mediated intracellular polymerization.

The synthesis of synthetic intracellular polymers offers groundbreaking possibilities in cellular biology and medical research, allowing for novel experiments in drug delivery, bioimaging and targeted cancer therapies. These macromolecules, composed of biocompatible monomers, are pivotal in manipulating cellular functions and pathways due to their bioavailability, cytocompatibility and distinct chemical properties. This protocol details two innovative methods for intracellular polymerization. The first one uses 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) as a photoinitiator for free radical polymerization under UV light (365 nm, 5 mW/cm2). The second method employs photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization with visible light (470 nm, 100 mW/cm2). We further elaborate on isolating these intracellular polymers by streptavidin/biotin interaction or immobilized metal ion affinity chromatography for polymers tagged with biotin or histidine. The entire process, from polymerization to isolation, takes ~48 h. Moreover, the intracellular polymers thus generated demonstrate significant potential in enhancing actin polymerization, in bioimaging applications and as a novel avenue in cancer treatment strategies. The protocol extends to animal models, providing a comprehensive approach from cellular to systemic applications. Users are advised to have a basic understanding of organic synthesis and cell biology techniques.

An electrochemical biosensor for the amplification of thrombin activity by perylene-mediated photoinitiated polymerization

BackgroundThrombin, a coagulation system protease, is a key enzyme involved in the coagulation cascade and has been developed as a marker for coagulation disorders. However, the methods developed in recent years have the disadvantages of complex operation, long reaction time, low specificity and sensitivity. Meanwhile, thrombin is at a lower level in the pre-disease period. Therefore, to accurately diagnose the disease, it is necessary to develop a fast, simple, highly sensitive and specific method using signal amplification technology. ResultsWe designed an electrochemical biosensor based on photocatalytic atom transfer radical polymerization (photo-ATRP) signal amplification for the detection of thrombin. Sulfhydryl substrate peptides (without carboxyl groups) are self-assembled to the gold electrode surface via Au–S bond and serve as thrombin recognition probes. The substrate peptide is cleaved in the presence of thrombin to generate –COOH, which can form a carboxylate-Zr(IV)-carboxylate complex via Zr(IV) and initiator (α-bromophenylacetic acid, BPAA). Subsequently, an electrochemical biosensor was prepared by introducing polymer chains with electrochemical signaling molecules (ferrocene, Fc) onto the electrode surface by photocatalytic (perylene, Py) mediated ATRP using ferrocenylmethyl methacrylate (FMMA) as a monomer. The concentration of thrombin was evaluated by the voltammetric signal generated by square wave voltammetry (SWV), and the result showed that the biosensor was linear between 1.0 ng/mL ∼ 10 fg/mL, with a lower detection limit of 4.0 fg/mL (∼0.1 fM). Moreover, it was shown to be highly selective for thrombin activity in complex serum samples and for thrombin inhibition screening. SignificanceThe biosensor is an environmentally friendly and economically efficient strategy while maintaining the advantages of high sensitivity, anti-interference, good stability and simplicity of operation, which has great potential for application in the analysis of complex samples.

Ion-Selective Potentiometry with Plasma-Initiated Covalent Attachment of Sensing Membranes onto Inert Polymeric Substrates and Carbon Solid Contacts.

The physical delamination of the sensing membrane from underlying electrode bodies and electron conductors limits sensor lifetimes and long-term monitoring with ion-selective electrodes (ISEs). To address this problem, we developed two plasma-initiated graft polymerization methods that attach ionophore-doped polymethacrylate sensing membranes covalently to high-surface-area carbons that serve as the conducting solid contact as well as to polypropylene, poly(ethylene-co-tetrafluoroethylene), and polyurethane as the inert polymeric electrode body materials. The first strategy consists of depositing the precursor solution for the preparation of the sensing membranes onto the platform substrates with the solid contact carbon, followed by exposure to an argon plasma, which results in surface-grafting of the in situ polymerized sensing membrane. Using the second strategy, the polymeric platform substrate is pretreated with argon plasma and subsequently exposed to ambient oxygen, forming hydroperoxide groups on the surface. Those functionalities are then used for the initiation of photoinitiated graft polymerization of the sensing membrane. Attenuated total reflection-Fourier transform infrared spectroscopy, water contact angle measurements, and delamination tests confirm the covalent attachment of the in situ polymerized sensing membranes onto the polymeric substrates. Using membrane precursor solutions comprising, in addition to decyl methacrylate and a cross-linker, also 2-(diisopropylamino)ethyl methacrylate as a covalently attachable H+ ionophore and tetrakis(pentafluorophenyl)borate as ionic sites, both plasma-based fabrication methods produced electrodes that responded to pH in a Nernstian fashion, with the high selectivity expected for ionophore-based ISEs.

Novel High-Performance Glyoxylate Derivative-Based Photoinitiators for Free Radical Photopolymerization and 3D Printing with Visible LED.

Investigations concerning the glyoxylate moiety as a photocleavable functional group for visible light photoinitiators, particularly in the initiation of free radical photopolymerization remain limited. This study introduces nine innovative carbazole-based ethyl glyoxylate derivatives (CEGs), which are synthesized and found to exhibit excellent photoinitiation abilities as monocomponent photoinitiating systems. Notably, these structures demonstrate robust absorption in the near-UV/visible range, surpassing the commercial photoinitiators. Moreover, the newly developed glyoxylate derivatives show higher acrylate function conversions compared to a benchmark photoinitiator (MBF) in free radical photopolymerization. Elucidation of the photoinitiation mechanism of CEGs is achieved through a comprehensive analysis involving the decarboxylation reaction and electron spin resonance spin trapping. Furthermore, their practical utility is confirmed during direct laser writing and 3D printing processes, enabling the successful fabrication of 3D printed objects. This study introduces pioneering concepts and effective strategies in the molecular design of novel photoinitiators, showcasing their potential for highly advantageous applications in 3D printing.

Triblock polymer PDMAEMA-co-PNIPAM-co-PMPC to deliver siKRAS for gene therapy in pancreatic cancer

Mutant KRAS sustained KRAS-GTP conformation and activated downstream signaling in pancreatic cancer. Inhibition of KRAS expression has been widely utilized for gene therapy of pancreatic cancer. In this study, a triblock cationic polymer, PDMAEMA-co-PNIPAM-co-PMPC (PDNM), was designed and synthesized as a gene carrier through photoinitiated free radical polymerization. The PDNM/siKRAS delivery system exhibited efficient cellular uptake and low bio-toxicity, as confirmed by fluorescence microscopy and flow cytometry. In vitro experiments using AsPC-1 cells showed that the nanoparticle transfection with PDNM/siKRAS demonstrated favorable anti-tumor effect, including enhanced apoptosis, inhibition of mitosis by arresting the cell cycle at the S phase, reduced Ki67 expression, and impaired cell migration ability. The anti-tumor effect was achieved primarily through KRAS inhibition and caspase 3 activation following siKRAS transfection. Additionally, in vivo experiments showed that the PDNM/siKRAS nanoparticles resulted in reduced tumor volumes and decreased Ki67 expression without apparent impairment of other organs. Notably, the transfection of nanoparticles in patient-derived organoids also demonstrated a similar inhibitory effect. Overall, PDNM holds promise as a potential carrier for siKRAS delivery and gene therapy, both in experimental and clinical applications.

Cationic UV-cured epoxy coating with inhibitor-loaded nanoparticles: photoinitiated cationic polymerization, mechanical properties and corrosion protection of steel

Cationic UV-cured epoxy coating with inhibitor-loaded nanoparticles: photoinitiated cationic polymerization, mechanical properties and corrosion protection of steel

Circularly Polarized Room Temperature Phosphorescence of Chiral Bromoxanthone Using a Chiral Self‐Assembled Liquid Crystal Polymer Frameworks

AbstractChiral self‐assembly has often been found to be an efficient strategy for the development of high‐performance circularly polarized luminescent (CPL) materials, through the regulation of the ordered helical superstructure blocks in liquid crystal media. Here, the design and synthesis of two pairs of axially chiral emitters (BBXT‐3‐Br and BOHXT‐3‐Br) are reported based on bromoxanthone. And the chiral self‐assembled liquid crystal polymer (LCP) framework (PRM257) is demonstrated by mixing of the emitters with liquid crystal monomer (RM257) through thermal annealing and photoinitiated polymerization. Both BBXT‐3‐Br@PRM257 and BOHXT‐3‐Br@PRM257 exhibited excellent room temperature phosphorescence (RTP) properties. In addition, BBXT‐3‐Br@PRM257 enantiomers showed afterglow with an average lifetime (τ) of 162.41 ms and emitted blue CPL (λem = 450 nm, ΦFL = 1.3%, |gFL| = 0.071), although weak circularly polarized RTP (CP‐RTP) is observed. Interestingly, BOHXT‐3‐Br@PRM257 with a less conjugated system emits red RTP (τ = 98.83 ms) and also intense CP‐RTP (λem = 612 nm, ΦPhos = 0.45%, |gRTP| = 0.057).

Multi-functional microparticles constructed by steerable phase separation process for synchronous uranium selective extraction and heat storage

Nuclear wastewater contains large amounts of uranium and waste heat, and hence synchronous uranium selective extraction and heat storage from nuclear wastewater are of prime importance. Herein, a series of distinctive dual-functional absorbents, such as P(St-VA)-1, P(St-VA)-2, P(St-VA)-3, were developed through photoinitiated interfacial polymerization via emulsion templates, using styrene and ethylene phosphate as co-monomers. The P(St-VA) has dual-functions, i.e., waste heat storage and uranium extraction. The uranium extraction feature is derived from the phosphoric acid group, while paraffin was encapsulated inside the P(St-VA). The concentration of sodium dodecyl sulfate (SDS) determines the rate and extent of phase separation between styrene and paraffin via tuning the size and stability of the emulsion, and hence the morphology and functionality of the P(St-VA). The P(St-VA) demonstrates excellent uranium adsorption performance with prominent selectivity. Furthermore, the P(St-VA) underwent multiple phase transitions between 25℃ and 70℃, displaying endothermic and exothermic behaviours and great heat storage potential. This study has provided an innovative path for the synchronous recycling of uranyl ions and waste heat from nuclear wastewater for practical applications.

Preparation of photo-grafted magnetic nano-silver composites and their catalytic studies on organic dyes

More active and stable catalyst is needed for degradation of organic dyes in wastewater. A new kind of polymethyl methacrylate (PMMA) microsphere hybridized with Ag and Fe3O4 was developed as catalyst. PMMA microspheres were prepared by photoinitiated dispersive polymerization, and then acrylic acid (AA) was photo-grafted on the surface of microspheres with 365 nm UV light to prepare PMMA-AA microspheres whose carboxyl group was up to 164 × 1021 per microsphere. Under the effect of NaBH4, the Ag nanoparticles on the surface of PMMA and PMMA-AA microspheres were successfully modified with the help of carboxyl groups on the surface of PMMA and PMMA-AA microspheres. Fe3O4 particles were adsorbed onto the microsphere surface to obtain two kinds of microspheres (PMMA@Ag@Fe3O4, PMMA-AA@Ag@Fe3O4) for the catalytic reduction of methylene blue (MB) and rhodamine B (Rh-B), respectively. PMMA-AA@Ag@Fe3O4 microspheres exhibited excellently catalytic performance that the apparent rate coeffcients of MB and Rh-B were 0.045 s−1 and 0.036 s−1 respectively. The catalytic efficiency of PMMA-AA@Ag@Fe3O4 heterogeneous catalyst can reach 90% even after 8 cycles for MB. It has excellent catalytic performance, high non-selective adsorption and good reusability. Excellent catalytic performance, high non-selective adsorption and reusability even in the presence of mixed dyes.

From RAFT emulsion polymerization to RAFT dispersion polymerization: a facile approach to tuning dispersities and behaviors of self-assembled block copolymers

We have demonstrated the successful transition from photoinitiated RAFT emulsion polymerization to photoinitiated RAFT dispersion polymerization by solely changing the solvent composition from water to water/ethanol.

Low hysteresis zwitterionic supramolecular polymer ion-conductive elastomers with anti-freezing properties, high stretchability, and self-adhesion for flexible electronic devices.

The fabrication of stretchable ionic conductors with low hysteresis and anti-freezing properties to enhance the durability and reliability of flexible electronics even at low temperatures remains an unmet challenge. Here, we report a facile strategy to fabricate low hysteresis, high stretchability, self-adhesion and anti-freezing zwitterionic supramolecular polymer ion-conductive elastomers (ICEs) by photoinitiated polymerization of aqueous precursor solutions containing a newly designed zwitterionic monomer carboxybetaine ureido acrylate (CBUIA) followed by solvent evaporation. The resultant poly(carboxybetaine ureido acrylate) (PCBUIA) ICEs are highly stretchable and self-adhesive owing to the presence of strong hydrogen bonds between ureido groups and dipole-dipole interactions of zwitterions. The zwitterion groups on the polymer side chains and loaded-lithium chloride endow PCBUIA ICEs with excellent anti-freezing properties, demonstrating mechanical flexibility and ionic transport properties even at a low temperature (-20 °C). Remarkably, the PCBUIA ICEs demonstrate a low hysteresis (≈10%) during cyclic mechanical loading-unloading (≤500%), and are successfully applied as wearable strain sensors and triboelectric nanogenerators (TENGs) for energy harvesting and human motion monitoring. In addition, the PCBUIA ICE-based TENG was used as a wireless sensing terminal for Internet of Things smart devices to enable wireless sensing of finger motion state detection.

Highly Adhesive and Self-Healing Zwitterionic Hydrogels as Antibacterial Coatings for Medical Devices.

Bacterial infection of medical devices has caused incalculable losses to maintenance costs and health care. A single coating with antibacterial function cannot guarantee the long-term use of the device, because the coating will be damaged and fall off during reuse. To solve this problem, the development of coatings with high adhesion and self-healing ability is a wise direction. In this paper, a multifunctional polyzwitterionic antibacterial hydrogel coating (PZG) composed of amphozwitterion monomer, anionic monomer, and quaternary ammonium cationic monomer was synthesized by dipping UV photoinitiated polymerization. The structure of PZGs was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Ascribing to the hydrogel internal electrostatic interaction, hydrogen bond, and cation-π interaction, the obtained PZGs exhibited high ductility (>1200% strain) and appropriate strength (>189 kPa). Remarkably, PZGs could also adhere firmly on different substrates through noncovalent interaction, and their adhesion could be controlled by adjusting the amount of zwitterionic. Reversible physical interactions in polymer networks endowed hydrogels with excellent self-healing properties. In addition, PZGs exhibit good antibacterial activity and biocompatibility due to the synergistic effect of quaternary ammonium cation and amphozwitterion monomer. This work provides a multifunctional antibacterial coating for medical equipment and has broad application prospects in the biomedical field.

Recent Advances in Visible Light Photoinitiating Systems Based on Flavonoids

The design of biosourced and/or bioinspired photoinitiators is an active research field as it offers a unique opportunity to develop photoinitiating systems exhibiting better biocompatibility as well as reduced toxicity. In this field, flavonoids can be found in numerous fruits and vegetables so these structures can be of interest for developing, in the future, polymerization processes, offering a reduced environmental impact but also better biocompatibility of the polymers. In this review, the different flavonoids reported to date as photoinitiators of polymerization are presented. Over the years, different modifications of the flavonoid scaffold have been examined including the grafting of well-known chromophores, the preparation of Type II photoinitiators or the introduction of photocleavable groups enabling the generation of Type I photoinitiators. Different families of flavonoids have also been investigated, enabling to design of high-performance photoinitiating systems.

Novel bis-chalcone-based carbazole derivative photoinitiators for visible light polymerization with good photobleaching and biocompatibility

Four novel bis-chalcone-based carbazole derivative photoinitiators (2E,5E)-2,5-bis((9-phenyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZA), 2,5-bis((E)-4-(9H-carbazol-9-yl)benzylidene)cyclopentan-1-one (KZB), (2E,5E)-2,5-bis((9-ethyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZC) and (2E,5E)-2,5-bis((5-(9-ethyl-9H-carbazol-3-yl)thiophen-2-yl)methylene)cyclopentan-1-one (KZD) were successfully designed and synthesized. Their maximum absorption wavelengths were 440 nm, 405 nm, 446 nm and 500 nm, respectively, and they all had high molar extinction coefficients. Furthermore, three-component photoinitiation system including bis-chalcone/iodonium/amine could quickly and efficiently trigger the photopolymerization of acrylates. For example, PEGDA coatings could cure in 10 s and the CC bond conversion exceeded 90 % in the end. Then we also conducted photosteady-state degradation, fluorescence quenching, cyclic voltammetry and ESR experiments to investigate the mechanisms of photopolymerization. Besides, all four bis-chalcones showed good photobleaching and biocompatibility, which was suitable for use in 3D printing and deep coating curing. For instance, the LCD 3D printer successfully printed clear and photobleached objects with KZD/iodonium/amine system. All these excellent properties indicated the industrial application potential of the four carbazole derivatives in visible light curing.