The 9,9-bisphenol-thioxanthene group is a structural unit with a high refractive index. However, few highrefractive-index (HRI) molecules have been designed using this group as the parent nucleus. In this study, two HRI epoxy/episulfide monomers, bisphenol thioxanthene epoxy/episulfide monomers (BTEOM and BTESM), were designed, and a high-yield synthetic route was developed. The thiol-epoxy click reaction further increased the refractive index of the polymers. The chemical structures of the monomers were characterized using nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. The optical properties (refractive indices-ellipsometry, transmittance-UV-Vis spectrophotometry) and, thermal stability (thermogravimetric analysis-TGA and, differential scanning calorimetry-DSC) of the polymer films were investigated. The optical properties of the monomers were simulated and calculated using density functional theory (DFT). The polymer films exhibited refractive indices of 1.694 and 1.701 at 589.3 nm, Abbe numbers of 21.030 and 20.618, and transmittance of over 90% at 425 nm. The maximum mass loss rate temperatures (Tmax) from the derivative TGA curves were 386 degrees C and 338 degrees C, and the glass transition temperatures (Tg) of the polymers were 125.67 degrees C and 135.18 degrees C. They demonstrated excellent optical and thermal properties. Furthermore, the trend of dynamically simulated refractive indices aligned well with the experimental values, further validating the effectiveness of the ground-state-dominated dynamic optical response and enabling accurate reproduction of the dispersion behavior across a broad wavelength range.

A novel photoinitiator, 2-(4-(2-hydroxy-2-methylpropanoyl)phenoxy)ethyl-4-methylpiperazine-1-carboxylate (N-2959) was developed, featuring an integrated alpha-hydroxy ketone moiety and a tertiary amine group. Initially, under 465 nm LED irradiation, camphorquinone (CQ) abstracts the alpha-hydrogen from the tertiary amine group of N-2959, generating an aminoalkyl radical that initiates the polymerization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA). This process yields the polymeric photoinitiator-PPEGMAm-2959, which demonstrates excellent water solubility, high initiation efficiency, and good migration stability. Subsequently, PPEGMAm-2959 was employed to initiate the aqueous dispersion polymerization of methacrylate monomers under 275 nm LED irradiation, producing amphiphilic block copolymers, of which chemical structure was analyzed by 1H NMR and GPC. This design enables sequential growth of two distinct polymer chains from N2959, providing a streamlined strategy for synthesizing polymeric photoinitiator and diblock copolymers.

Traditional solvent-based methods for polyurethane preparation suffer from large VOCs emissions, solvent residue, high energy consumption and poor safety. In contrast, silicone modification can effectively improve the hydrophobicity and chemical resistance of polyurethane. In this study, solvent-free reaction was adopted to synthesize polyurethane, with polytetramethylene ether glycol and isophorone diisocyanate as raw materials, single-terminal monohydroxy polysiloxane, double-terminal monohydroxy polysiloxane and single-terminal dihydroxy polysiloxane as functional monomers, and hydroxyethyl acrylate as the capping monomer. After the addition of a photoinitiator, high-performance hydrophobic polyurethane coatings were fabricated upon 365 nm LED-UV curing. The modified polyurethane exhibits a reduced viscosity (decreased by 20%). The cured coatings possess improved mechanical properties (increased by 20-60%), excellent hydrophobicity (water contact angle of 111.33 degrees), favorable water resistance (water absorption of 1.51%), outstanding abrasion resistance (wear index reduced by 10%) and superior chemical resistance. Owing to the comprehensive and outstanding performances, the prepared polyurethane can be used as a resin to develop hydrophobic coatings through formula adjustment.

In the practical application of polyurethane acrylate (PUA), the relatively high viscosity usually brings difficulties to the processing process, especially limiting its further promotion and application in fields such as 3D printing and electronic packaging materials. This phenomenon is mainly caused by the strong hydrogen bond interaction between PUA molecular chains. To solve the above problems, starting from molecular structure design, this study synthesized low-viscosity polyurethane acrylate derivatives through two-step chemical modification. Firstly, PUA was reacted with paraformaldehyde to prepare hydroxymethylated polyurethane acrylate (D-PUA); subsequently, D-PUA was subjected to acylation reaction with acetic anhydride to further prepare acetylated polyurethane acrylate (Y-D-PUA). The experimental results show that compared with unmodified PUA, the viscosity of D-PUA can be reduced by up to 48.45%, the viscosity of Y-D-PUA can be reduced by up to 51.55%. In addition, after adding 2% photoinitiator 1173 and UV curing, the bending resistance of the films formed by D-PUA and Y-D-PUA is improved compared with PUA, while other properties remain basically unchanged. The two-step modification strategy of hydroxymethylation followed by acetylation can effectively reduce the viscosity of the PUA system, thus providing a feasible material basis for its expanded application in 3D printing and electronic packaging materials.

Understanding the molecular origin of thermo-optical transitions in ionic-liquid ionogels is essential for rationally designing robust, nonvolatile thermoresponsive devices. Here, a UCST-type poly(hydroxypropyl acrylate) (PHPA)-[EMIM][TFSI] ionogel was constructed via a one-step UV-induced photopolymerization and displayed reversible switching between opaque and transparent states upon heating. By integrating variable-temperature Fourier transform infrared spectroscopy (VT-FTIR) with 2D correlation infrared spectroscopy (2D-COS IR), the transition was traced to a temperature-driven redistribution of noncovalent interactions within the polymer/ionic-liquid matrix. At low temperature, cooperative hydroxyl-centered association dominated the microstructure, while heating progressively weakened polymer-associated hydrogen-bond motifs and promoted polymer-ionic-liquid association involving both hydroxyl and carbonyl environments. This interaction rebalancing diminished microheterogeneity and reduced light scattering, thereby generating the UCST-type opaque-to-transparent transition. The ionogel maintained stable optical switching over repeated thermal cycles and exhibited high sensitivity near the transition region, highlighting its promise for high-resolution temperature sensing and adaptive optical modulation in nonvolatile soft materials.

Temperature-sensitive gels are attractive in various fields, including smart windows, information encryption, and actuators. Herein, we select ethylene glycol as the solvent and prepare a poly(4-acryloylmorpholine) (PACMO) organogel with UCST phase transition behavior via photopolymerization. This temperature-sensitive organogel, with transition temperatures adjustable between 10 and 62 °C, displays high temperature sensitivity, a narrow transition window, and excellent cycling stability. The incorporation of comonomers, cosolvents, and cross-linkers significantly affects the transition behavior of the organogel through changing the transition temperature or broadening the transition window from 2 to 25 °C. Variable-temperature infrared spectroscopy and theory calculations reveal that the ether bond of PACMO competes with the intermolecular hydrogen bonds of ethylene glycol. As the temperature rises, the intermolecular hydrogen-bond interaction between ethylene glycol molecules weakens, while the hydrogen-bond interaction between the ether bond and ethylene glycol strengthens, leading to changes in transparency of the organogel. The applications of the organogel in the fields of temperature-controlled information displays and smart temperature labels are demonstrated. This design broadens the types of temperature-sensitive gel materials to organogels, opening a pathway toward applications with multifunctional optical requirements.

Foamed polymers have been widely applied in aerospace, automotive, and other fields. However, the rapid fabrication of locally foamed materials from low-viscosity precursor solutions remains a significant challenge. To address this issue, this study proposes a foaming technology based on azo initiators via a photo-initiated, thermally driven self-accelerating coupling mechanism: 365 nm light irradiation triggers the photodegradation of azo initiators to generate N-2 and free radicals, which initiate monomer polymerization. The heat released from the polymerization reaction forms a self-accelerating effect, promoting the continuous decomposition of the initiator, finally achieving the in-situ construction of foamed materials within seconds (as fast as < 1 s). The introduction of additives such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), water, and N,N'-methylenebisacrylamide (MBAA) can enhance preparation efficiency, achieve sample transparency, and precisely optimize the structure. This technology boasts distinct features: the precursor is a low-viscosity "initiator-monomer" solution without the need for complex pretreatment; target areas can be selectively foamed or remain transparent by regulating the UV irradiation region and intensity; the resulting products are applicable for ultraviolet radiation shielding and pressure-sensitive actuators. Meanwhile, it possesses excellent system versatility: through the selection of oil-soluble azo initiators (AIBMe, ABVN, AIBN) and water-soluble azo initiator (AIBA), it can stably achieve photopolymerization-induced foaming for four monomers in oil-phase and water-phase systems respectively. This study provides a convenient pathway for the rapid preparation and local functional modification of foamed materials, holds significant application potential in high-end fields such as precision device protection and customized thermal insulation coatings.

High-refractive-index (HRI) liquid monomers containing unsaturated acrylate double bonds possess advantages such as photocurability at room temperature and environmental friendliness. However, introducing acrylate groups often reduces the refractive index of monomers. Although small-molecule sulfur-containing structures have high refractive indices, their pungent odors restrict their applications. In this study, a series of sulfur-containing monomers have been successfully prepared through the optimized combination of sulfur elements, benzene rings, and acrylates. These monomers are in a liquid state, and the refractive index performance has reached an advanced level among photocurable monomers. Furthermore, the optical properties (refractive indices, transmittances), curing properties (double-bond conversion and rate of polymerization), and thermal stability (TGA) of the polymer films have been emphatically investigated. The polymer film has a refractive index of 1.648-1.672 at 589 nm, an Abbe number of 22.20-29.32, a transmittance of >90 % at 550-800 nm, a double-bond conversion of 70-92 %, and a maximum weight-loss rate (T-max) temperature of 354-363 degrees C, glass transition temperature (T-g) of 45.91 degrees C-58.45 degrees C. It exhibits excellent optical properties, curing properties, and thermal stability, opening up new possibilities for the applications of HRI materials.

The introduction of substituents affects the planarity of the molecule, resulting in different physical and chemical properties. This study synthesized four one-component visible light photoinitiators with different substituents derived from 1-naphthylamine. They were amine-free (BTX), primary amine (BTX-A), secondary amine (BTXMA), and tertiary amine (BTX-DMA). The photophysical and photochemical properties were explored using UV-visible absorption spectroscopy combined with DFT theory computational simulations. They had excellent absorption properties in the visible light range (epsilon: 3200-6300 L mol(-1) cm(-1)). The structure of amine substitutions in the initiators showed different redshift phenomena. The maximum absorption wavelength of BTX in the visible region is 388 nm; only a 7 nm red shift occurred for the maximum absorption wavelength of BTX-DMA. While BTX-A had a maximum absorption wavelength of red shifting by 41 nm, the red shift for BTX-MA was about 53 nm, and its UV absorption tail extended to 520 nm. This phenomenon was known to be the result of the combined effect of electronic donor and molecular planarity according to the DFT theoretical calculations. The photopolymerization kinetics of four initiators used for double bond monomers was investigated by real-time FT-IR. The results indicated that polymerization could occur for all the designed systems; the highest double bond conversion could reach 92 % when BTX-DMA was used as a visible-light photoinitiator for the monomer of 2-hydroxyethyl acrylate (HEA).

With the rapid and comprehensive development of research on high-refractive index materials and the demand for these materials in different fields, the structural design and application of the monomers containing unsaturated groups have been significantly explored, and the properties have improved in recent years. The structural design, polymerization method, optical properties, and application exploration of unsaturated double-bond high-refractive index monomers are analyzed in detail. Unsaturated high-refractive index monomers (UHRIMs) comprise high molar refractive index groups and unsaturated groups. In the structural design, the main types of unsaturated double bonds are vinyl (alkyne)/allyl, vinyl ether/allyl ether, (methyl)acrylate, cyclic olefin, maleimide, and others. The type of unsaturated group determines the polymerization method employed. The main polymerization methods include thiol-ene click reaction, thermal-initiated polymerization, photo-initiated polymerization, coordination polymerization, etc. In addition, the UHRIMs have relatively small molecular weight, high solubility, and mild molding conditions, which will have potential wide applications in nanoimprint, holographic technology, thermal infrared imaging, microlenses, optical devices, waveguide materials, coatings, etc.

To enhance the photosensitivity of ketones, which are prone to side isomerization reactions during free radical photopolymerization, a novel strategy involving the use of an alkyl bridge was introduced. This approach was assessed by comparing the performance of two ketone photoinitiators: (E)-2-((1H-pyrrol-2-yl)methylene)-4methyl-3,4-dihydronaphthalen-1(2H)-one (PDN) and (2E,2 ' E)-2,2 '-((octane-1,8-diylbis(1H-pyrrole-1,2-diyl))bis(methaneylylidene))bis(4-methyl-3,4-dihydronaph- thalen-1(2H)-one) (bis-PDN). The synthesis of bis-PDN involved linking two PDN molecules via a long alkyl chain derived from 1,8-dibromooctane. It was shown that this alkyl bridge not only provides steric hindrance that limits the isomerization of PDN but also imparts a significant increase in the molar extinction coefficient of the newly synthesized bis-PDN to 43,779 M-1 cm -1 by following the strategy of multiple chromophores. Consequently, bis-PDN demonstrated a notably high initiating efficiency for LED-sensitive polymerization. The efficacy of this alkyl bridge modification was further validated through DFT calculations, steady-state photolysis, NMR testing, polymerization kinetics analysis, and 3D printing experiments. The alkyl bridge technique offers considerable promise for the development of ketone compounds with enhanced photo-activity.

Multi-branched hydrogel tubes have promising applications in various fields. However, it remains a great challenge to prepare such structures using a convenient method. Herein, an innovative method inspired by the bud-growth of plants (bud-notching and bud-picking) was proposed to prepare multi-branched hydrogel tubes based on sodium alginate/copper ions (Na-Alg/Cu2+). The bud-notching technique refers to the selective decrosslinking of Na-Alg/Cu2+ gels by controlled ethanolamine treatment, resulting in an "opening" in the tube wall. By adjusting the location and number of bud-notching on the primary tube and combining the apical growth technique, branched hydrogel tubes with diverse dimensions (two and three-dimensional) and structures ("zigzag"-shaped and "helical"-shaped) could be prepared on demand, without the need for templates and expensive equipment. Furthermore, biomimetic multi-segment hydrogel tubes were fabricated as simplified models to investigate the stability at the connection sites. The results demonstrated that the secondary hydrogel tubes prepared through multi-step growth retained approximately 70% of the elongation at break and 90% of the fracture force compared to the directly formed monolithic hydrogel tubes. Furthermore, the perfusion experiments showed that connections between branches were stable, which made the developed multi-branched hydrogel tubes have promising applications in some in vitro models and fluidic transport application areas. This kind of biomimetic method will also be meaningful for broadening the preparation of multi-branched materials.

Hydrogels exhibiting lower or upper critical solution temperature (LCST/UCST) behavior undergo reversible phase transitions accompanied by volumetric shrinkage or optical switching, are widely used in smart windows, anti-counterfeiting, temperature-sensitive robots, and other fields. Nevertheless, their application is restricted by single-step thermal transitions inherent to isotropic polymer networks, which makes it impossible to accomplish several temperature transitions of hydrogels. Furthermore, compared to single-stimulus response, multiple responses present additional difficulties. To address these challenges, adjustable anisotropic Poly (hydroxypropyl acrylate-co-acryloyloxyethyl trimethyl ammonium chloride)/Poly (N-isopropyl acrylamide) (HD/NIPAM) hydrogels are prepared by limited domain swelling method. These hydrogels achieve tunable transition temperatures (-1.07 degrees C-36.04 degrees C) and broad transition windows (9.4 degrees C-25.3 degrees C) by modulating NIPAM concentration and limited thickness. Remarkably, 1HD20/N15 hydrogels exhibit exceptional time and cycle stability during their reversible transparency shift (97% to 1.8%). This performance enables applications in gradient-selective smart windows and soft thermal indicators with spatially resolved signaling. Furthermore, through the transition of matrix hydrogel (poly(hydroxypropyl acrylate-co-acryloyloxyethyl trimethyl ammonium chloride) (HD) hydrogel to poly(hydroxypropyl acrylate-co-acryloxyethyl trimethyl ammonium dysprosium thiocyanate) (HDy) hydrogel), the transition from thermal single stimulus to thermal/light dual stimulus response was achieved due to the Dy element.

Ionogels have garnered significant attention in materials science due to their exceptional ionic conductivity, high thermal stability, electrochemical stability, and unique potential demonstrated in wearable electronics and energy storage technologies. Nevertheless, the design of natural polymer-based ionogels featuring outstanding mechanical properties still poses a formidable challenge. To address this issue, this study employs microcrystalline cellulose (MCC), a natural renewable material, as the matrix. By introducing an ionic liquid solvent and acrylic acid (AA) molecules to induce cellulose self-assembly, a physically cross-linked network structure was constructed. Further, through photopolymerization, an MCC/polyacrylic acid (PAA) double-network ionogel was successfully prepared. The resulting ionogel exhibits outstanding tensile strength (3.76 MPa), toughness (1.97 MJ/m3), elastic modulus (7.45 MPa), and ionic conductivity (0.22 mS/cm), along with excellent transparency (83.4%), high thermal stability, and a low glass transition temperature (-29 degrees C). The flexible sensor based on the MCC/PAA ionogel demonstrates high sensitivity to temperature (response time: 112 s, sensitivity: 3.97%degrees C-1) and strain (gauge factor: 1.1, response time: 500 ms, strain detection limit: 1%, reusable), can effectively monitor human motion across various ranges. This study develops an ionogel material with superior performance and biocompatibility, providing a solid foundation and technical support for applications in flexible electronics and energy storage, showcasing broad potential for future advancements.

A series of fluid intermediates with nonspherical shapes are produced when a droplet impacts the surface of a miscible liquid, and the fixation of these fluid intermediates through a gelation or precipitation process is known as the "freezing method". However, the traditional existing vorticity ring derived gel particles were prepared from macromolecules and rely on chemical cross-linking reactions, limiting the choice of material. In this work, a strategy of preparing specially shaped gel particles by using a light-curable monomer through the methods of photopolymerization and vortex ring freezing was proposed. Based on the principle of matching the rapid reaction rate of light curing with the droplet deformation rate, a series of specially shaped (spherical, ellipsoidal, bowl, and tadpole) gel particles were prepared. The factors influencing droplet shape formation, such as light intensity, needle size, drop height, and the properties of the receiving bath, were analyzed. Three physical parameters, Reynolds number, Weber number, and viscosity ratio, were introduced to elucidate and predict the variations in gel particle morphology. This study opens up a green way for preparing specially shaped gel particles and holds promise for a wide range of future applications.

High-performance flexible pressure sensors have demonstrated significant promise in electronic skins, energy harvesting, soft robotics, and other applications. However, achieving concurrent optimization of sensitivity and a broad pressure response range remained challenging, leading to limitations in detection thresholds, sensing range, and mechanical robustness. In this work, gradient stress hydrogels were prepared through a limited domain swelling method. It was made up of "soft" hydrogel (Poly (hydroxyethyl acrylate -co- acryloyloxyethyl trimethyl ammonium chloride) (HD20)) and "hard" hydrogel (Poly hydroxypropyl acrylate (HPA50)). "Soft" hydrogel provided high electrical conductivity (1.0510 S/m) and high sensitivity (4.7271 MPa-1), whereas "hard" hydrogel offered a wide sensing range (from 0.000486 to 1.17 MPa). Additionally, it could be applied to various material interfaces (glass, plastic, metal, polytetrafluoroethylene, silicone rubber, skin) due to & horbar;OH/N+ groups and low temperature environments (-14 degrees C). And it demonstrated outstanding cycle stability and the capacity to identify various strains. This facile and effective method was useful to design and preparing highly sensitive pressure sensors at a wide pressure working range.

High photo-resistance and photo-sensitivity is a persistent challenge in photopolymerization. In this research, sunlight stability of commercial photoinitiator camphorquinone (CQ) based photo-curing materials is enhanced by adding the mixture of (E)-1-(cyclohex-1-en-1-yl)-3-(1H-pyrrol-2-yl)prop-2-en-1-one (E-CHPO) and its cis isomer Z-CHPO used as a solution mask. These compounds have a broad absorption range and a high molar extinction coefficient, ranging from 250 nm to 550 nm, which inhibits the action of CQ. Furthermore, CQ could also absorb light for polymerization as E/Z-CHPO gradually fades due to its [2 + 2] cycloaddition reaction under LED@465 nm irradiation with high light intensity. Additionally, corresponding mechanism was investigated.

Hydrogels are widely used in biological dressing, tissue scaffolding, drug delivery, sensors, and other promising applications owing to their water-rich soft structures, biocompatibility, and adjustable mechanical properties. However, most of the conventional hydrogels are isotropic. The anisotropic structures existed widely in the organizational structure of plants and animals, which played a crucial role in biological systems. In this work, a method of limited domain swelling to prepare anisotropic hydrogels is proposed. Through spatially controlled swelling, the extension direction of hydrogels can be limited by a tailored mold, further achieving anisotropic hydrogels with concentration gradients. The external solution serves as a swelling solution to promote swelling and extension of the hydrogel matrix in a mold which can control the extension direction. Due to the diversity of external solutions, the method can be applied to prepare a variety of stimulus-responsive polymers. The limited domain swelling method is promising for the construction of anisotropic hydrogels with different structures and properties. A method named the limited domain swelling method is proposed for preparing gradient hydrogels. An external solution is regarded as a "nutrient" to promote the swelling of the hydrogel matrix, the mold controls the extension direction. The extension direction of hydrogels is limited by a tailored mold. Anisotropic structures are demonstrated through mechanical properties, conductivity, all-band ultraviolet transmittance, etc. image

Photocuring 3D printing of hydrogels, with sophisticated, delicate structures and biocompatibility, attracts significant attention by researchers and possesses promising application in the fields of tissue engineering and flexible devices. After years of development, photocuring 3D printing technologies and hydrogel inks make great progress. Herein, the techniques of photocuring 3D printing of hydrogels, including direct ink writing (DIW), stereolithography (SLA), digital light processing (DLP), continuous liquid interface production (CLIP), volumetric additive manufacturing (VAM), and two photon polymerization (TPP) are reviewed. Further, the raw materials for hydrogel inks (photocurable polymers, monomers, photoinitiators, and additives) and applications in tissue engineering and flexible devices are also reviewed. At last, the current challenges and future perspectives of photocuring 3D printing of hydrogels are discussed.