Trifunctional Monomer Research Articles

A novel efficient flame-retardant curing agent for epoxy resin based on P-N synergistic effect: Bio-based benzoxazine phosphate ester

Most epoxy resins on the market have low thermal stability and flammable defects. As a potential curing agent for epoxy resin, polybenzoxazine (PBz) can effectively improve the thermal properties of the resin due to its low heat release capacity (HRC) and rigid aromatic ring support, and its raw materials can be derived from renewable resources. Here, we have successfully developed a molecular design strategy to obtain a trifunctional benzoxazine monomer with phosphate ester. Firstly, guaiacol-ethanolamine benzoxazine monomer (GE) was synthesized by Mannich condensation using guaiacol and ethanolamine as raw materials. Then trifunctional benzoxazine phosphate ester (TBP) was synthesized by the nucleophilic reaction of GE with phosphorus oxychloride. Finally, the epoxy resin DGEBA was cured by TBP to obtain a PBz modified epoxy resin (EP-TBP polymer) with Tg of 113.7 °C and char yield of 37.4 %. Due to the introduction of TBP rich in phosphorus and nitrogen, it releases phosphorus radicals and nitrogen-containing inert gases during combustion, which leads to quenching effect and dilution effect. In addition, TBP can also promote the dehydration and dehydrogenation of the polymer and accelerate the formation of the aromatic hybrid char layer. Therefore, the THR of TBP modified epoxy resin is 49.3 % lower than that of epoxy resin without TBP, and the char yield is 47 times higher. And when the phosphorus content is 1.76 %, the flame-retardant grade can reach V-0. In addition, the introduction of TBP also enhanced the mechanical properties, adhesion properties and hydrophobicity properties of the polymer. It is worth mentioning that under alkaline conditions, the phosphate ester in the structure of EP-TBP polymer will undergo ammonolysis reaction with ethanolamine, and the resulting oligomers will be dissolved in it, thereby achieving rapid degradation of EP-TBP polymer. This work is to develop a high-performance multifunctional epoxy resin flame retardant curing agent based on renewable raw materials, and provide important insights for the subsequent development of halogen-free bio-based PBz flame retardant materials.

Carbazole-fused coumarin bis oxime esters (CCOBOEs) as efficient photoinitiators of polymerization for 3D printing with 405 nm LED

In this research, the innovative design and successful synthesis of two visible light photoinitiators, namely CCOBOE0 and CCOBOE1, have been confirmed through nuclear magnetic resonance (NMR) and mass spectrometry (MS). Both compounds exhibit strong absorption properties at 385, 405 and 450 nm, and FT-IR analyses have substantiated the ability of CCOBOE1 to initiate the polymerization of a trifunctional acrylate monomer (TMPTA) under these three light sources. The optimal conditions for maximizing the photoinitiation potential of CCOBOE1 were determined to be at a concentration of 2 × 10−5 mol.g−1 and under 405 nm LED irradiation. Photolysis experiments, theoretical calculations, detection of CO2 absorption peaks, and ESR experiments have all confirmed the generation of methyl radicals by CCOBOE1. Utilizing the identified optimal conditions, a “XYZ” pattern with a thickness of 963 μm and a 3D-object were successfully obtained via direct laser write (DLW) and digital light processing (DLP) 3D-printing upon irradiation at 405 nm. Additionally, differential scanning calorimetry (DSC) analyses demonstrated the promising performance of CCOBOE1 in initiating the thermal polymerization of acrylate monomers. In summary, the difunctional CCOBOE1 showed outstanding performance in both photo-initiation and thermal initiation of acrylate monomers. It provides a novel direction for the development of novel OXEs with dual activation modes.

Tailoring the gas transport properties of network polyimide membranes by bromination/debromination

Constructing membranes that possess both exceptional gas transport property and strong resistance to CO2-induced plasticization is a crucial need in membrane separation, yet it still stands as an ongoing challenge. In present study, we firstly added the bromine atom into the 2, 2′-bis(trifluoromethyl)benzidine (TF) to synthesis two new bromine substituted diamines, and subsequently one of the brominated diamines was employed as a comonomer alongside commercial tris(4-aminophenyl)amine (TAPA) and dianhydride 6FDA to prepare the network polyimide (PI) membrane via copolymerization. Following this, these new brominated PIs would undergo debromination process during the subsequent heating treatment. As a result, the bromination/debromination effect created new microporosity, which increased the d-spacing and BET surface area of the membrane, thereby largely enhancing the crosslinked PI membrane’s gas separation performance. Moreover, the robust network structures achieved through in-situ crosslinking way, derived from a segment of trifunctional TAPA monomers, enhance the resultant membrane's resistance to CO2 plasticization issue. An exemplified membrane referred to as 6 F-TA/TF-dBr-450 membrane displays outstanding CO2/CH4 separation capabilities, with a CO2 permeability of 1420.56 Barrer and a CO2/CH4 selectivity of 39.67, surpassing the 2008 Roberson upper bound by a considerable margin. Besides, this membrane demonstrates outstanding durability against CO2-induced plasticization, showcasing its strength under pressures of at least 35 Bar.

Bioreducible Amphiphilic Hyperbranched Polymer-Drug Conjugate for Intracellular Drug Delivery.

This paper reports synthesis of a bioreducible hyperbranched (HB) polymer by A2+B3 approach from commercially available dithiothreitol (DTT) (A2) and an easily accessible trifunctional monomer (B3) containing three reactive pyridyl-disulfide groups. Highly efficient thiol-activated disulfide exchange reaction leads to the formation of the HB polymer (Mw = 21000; Đ = 2.3) with bioreducible disulfide linkages in the backbone and two different functional groups, namely, hydroxyl and pyridyl-disulfide in the core and periphery, respectively, of the HB-polymer. Postpolymerization functionalization of the hydroxyl-groups with camptothecin (CPT), a topoisomerase inhibitor and known anticancer drug, followed by replacing the terminal pyridyl-disulfide groups with oligo-oxyethylene-thiol resulted in easy access to an amphiphilic HB polydisulfide-CPT conjugate (P1) with a very high drug loading content of ∼40%. P1 aggregated in water (above ∼10 μg/mL) producing drug-loaded nanoparticles (Dh ∼ 135 nm), which showed highly efficient glutathione (GSH)-triggered release of the active CPT. Mass spectrometry analysis of the GSH-treated P1 showed the presence of the active CPT drug as well as a cyclic monothiocarbonate product, which underpins the cascade-degradation mechanism involving GSH-triggered cleavage of the labile disulfide linkage, followed by intramolecular nucleophilic attack by the in situ generated thiol to the neighboring carbonate linkage, resulting in release of the active CPT drug. The P1 nanoparticle showed excellent cellular uptake as tested by confocal fluorescence microscopy in HeLa cells by predominantly endocytosis mechanism, resulting in highly efficient cell killing (IC50 ∼ 0.6 μg/mL) as evident from the results of the MTT assay, as well as the apoptosis assay. Comparative studies with an analogous linear polymer-CPT conjugate showed much superior intracellular drug delivery potency of the hyperbranched polymer.

Xylose- and Nucleoside-Based Polymers via Thiol-ene Polymerization toward Sugar-Derived Solid Polymer Electrolytes.

A series of copolymers have been prepared via thiol-ene polymerization of bioderived α,ω-unsaturated diene monomers with dithiols toward application as solid polymer electrolytes (SPEs) for Li+-ion conduction. Amorphous polyesters and polyethers with low Tg's (-31 to -11 °C) were first prepared from xylose-based monomers (with varying lengths of fatty acid moiety) and 2,2'-(ethylenedioxy)diethanethiol (EDT). Cross-linking by incorporation of a trifunctional monomer also produced a series of SPEs with ionic conductivities up to 2.2 × 10-5 S cm-1 at 60 °C and electrochemical stability up to 5.08 V, a significant improvement over previous xylose-derived materials. Furthermore, a series of copolymers bearing nucleoside moieties were prepared to exploit the complementary base-pairing interaction of nucleobases. Flexible, transparent, and reprocessable SPE films were thus prepared with improved ionic conductivity (up to 1.5 × 10-4 S cm-1 at 60 °C), hydrolytic degradability, and potential self-healing capabilities.

Control of thermal and mechanical properties by double-cyclopolymerization and copolymerization of trifunctional POSS with varying organic substituents

Abstract Phenyl- and trifluoropropyl-substituted corner-opening type cage silsesquioxane (CO-POSS) monomers capped with methacrylethoxypropyldimethylsiloxy groups at the three silanol moieties were prepared by the hydrosilylation of trisdimethylsilyl-capped heptaphenyl- and heptatrifluoropropyl-substituted trisilanols with ethylene glycol monoallyl ether and subsequent reaction with methacryloyl chloride. Reversible addition-fragmentation chain transferpolymerization was performed on these monomers, and their structures and properties were compared to those of their previously-reported isobutyl-substituted counterparts. The polymer with a phenyl group exhibited enhanced thermal and mechanical properties, whereas the polymer with a trifluoropropyl group exhibited not only water repellency but also oil repellency. In addition, trifunctional CO-POSS monomers with different organic substituents could be used for double-cyclocopolymerization, and tuning of their properties was achieved. Furthermore, the trifunctional CO-POSS monomer could be used for double-cyclocopolymerization with methyl methacrylate without cross-linking.

Synthesis of AB2 type hyperbranched polymer by CuAAC based 1,3-dipolar cycloaddition and its application in delivering curcumin to cancer cell cultures in-vitro

Hyperbranched polymers are three-dimensional macromolecules with unique physical and chemical properties, such as high solubility, low viscosity, and many functional groups at the terminals, as well as possible applications in several fields. Herein, we report the synthesis of a trifunctional AB2 monomer in a three-step process followed by "Click" polymerization via copper-catalyzed azide-alkyne cycloaddition to prepare a polytriazole-based hyperbranched polymer. Synthesized monomer and polymer were subsequently characterized by 1H and 13C NMR spectroscopy, and size-exclusion chromatography. The AB2 type hyperbranched polymer was self-assembled into lipid-polymer hybrid nanoparticles (HBP-NPs) through a nanoprecipitation approach, and curcumin (CUR) was incorporated into the HBP-NPs. The CUR-loaded HBP-NPs were characterized by particle size analysis, zeta potential, polydispersity index, morphology, drug entrapment efficiency, in vitro drug release, cellular uptake, and anticancer potential against HepG2 and NCI-H460 cell lines. The results indicated the CUR-loaded HBP-NPs demonstrated enhanced cell inhibition due to the improved delivery of CUR upon incorporation into HBP-NPs.

The interaction of triglycidyl phosphate with europium nitrate and properties of obtained metal-containing polymer

The interaction of phosphorus-containing epoxy trifunctional monomer – triglycidyl phosphate (TGPhT), with europium (III) nitrate hexahydrate is studied. A dissolution of europium salt added into TGPhT is occurred due to the interaction of the cation with phosphoryl groups and oxygen atoms of the epoxy ring, that is accompanied by the opening reaction and led to the formation of a polymer. The interaction of triepoxide with salt is investigated by FTIR-spectroscopy and differential scanning calorimetry (DSC). The thermal stability of the samples is determined by combined method of thermogravimetry and differential scanning calorimetry (TG/DSC), coupled with a quadrupole mass spectrometry to identify the gaseous products evolved during the thermal analysis of the samples. The kinetic parameters of the curing reaction are computed by using Thermokinetics software. The interaction of TGPhT with europium nitrate is suggested to occur through opening of epoxy rings in the presence of europium ions via the mechanism of cationic polymerization. The cured epoxy polymer exhibits luminescent properties.

Molecular dynamics simulation of molecular network structure and mechanical properties of polymer matrix in PBT propellant

3,3-Bis(azidomethyl)oxetane (BAMO)/tetrahydrofuran (THF) copolymer (PBT) constitutes the polymer matrix of PBT solid propellant and influences the mechanical properties of the propellant. In this work, the molecular network structure of the PBT propellant matrix was constructed by molecular dynamics method, the influence of different component contents on the mechanical properties was studied, and the structure - mechanical properties relationship at the molecular level was established. The simulation results showed that changes in the content of crosslinker (TMP) and chain extender (DEG) had slight effects on Young's modulus. The tensile strength of the polymer matrix network was positively correlated with the molecular chain length and the number of cross-linking sites formed by TMP. When the isocyanate index R was less than 1, increasing the content of TMP crosslinker led to low conversion rate due to insufficient curing agent, thereby reducing the number of cross-linking sites and the strength of the system. When the isocyanate index R was less than 0.87, the increase of DEG content increased the chain length of the main chain and strengthened the system. Due to the competitive reaction with the curing agent, the difunctional (-OH) chain extender monomer showed stronger reactivity than the trifunctional crosslinker monomer, and the excess chain extender reduced the number of crosslinking sites, destroyed the crosslinking network structure and reduced the strength.

Adjustable Thermo-Responsive, Cell-Adhesive Tissue Engineering Scaffolds for Cell Stimulation through Periodic Changes in Culture Temperature.

A three-dimensional (3D) scaffold ideally provides hierarchical complexity and imitates the chemistry and mechanical properties of the natural cell environment. Here, we report on a stimuli-responsive photo-cross-linkable resin formulation for the fabrication of scaffolds by continuous digital light processing (cDLP), which allows for the mechano-stimulation of adherent cells. The resin comprises a network-forming trifunctional acrylate ester monomer (trimethylolpropane triacrylate, or TMPTA), N-isopropyl acrylamide (NiPAAm), cationic dimethylaminoethyl acrylate (DMAEA) for enhanced cell interaction, and 4-acryloyl morpholine (AMO) to adjust the phase transition temperature (Ttrans) of the equilibrium swollen cross-polymerized scaffold. With glycofurol as a biocompatible solvent, controlled three-dimensional structures were fabricated and the transition temperatures were adjusted by resin composition. The effects of the thermally induced mechano-stimulation were investigated with mouse fibroblasts (L929) and myoblasts (C2C12) on printed constructs. Periodic changes in the culture temperature stimulated the myoblast proliferation.

Vanillin-based liquid crystalline polyimine thermosets and their composites for recyclable thermal management application

The development of bio-based thermosets with favorable mechanical properties, high glass transition temperature (Tg), and recyclability for thermal management applications remains a huge challenge. In this study, a trifunctional aldehydes monomer was prepared from vanillin followed by curing with two kinds of diamine for novel polyimine networks. The results showed that the polyimine networks cured with 4,4′-diaminodiphenyl methane demonstrated the liquid crystalline polyimine thermosets with a high Tg of 193 °C, a high tensile strength up to 84 MPa, and excellent thermal stability (the values of degradation temperature for 5 wt% weight loss, Td5 = 373 °C), while the polyimine networks cured with 4,4′-methylenebis(cyclohexylamine) demonstrated amorphous polyimine thermosets with inferior mechanical and thermos-physical performances, due to the crosslinked liquid crystal structure, the rigid benzene ring and the π-π stacking effect of the former. Furthermore, the polyimine nanocomposites were constructed by incorporating graphene nanoplatelets (GnPs) into these bio-based thermosets. With only 8 wt% GnPs, the nanocomposites showed a remarkable thermal conductivity of 1.8 W m−1 K−1. Interestingly, both the polyimine networks and their composites demonstrated complete recyclability in mild acid conditions owing to the existence of dynamical Schiff-base structures. The bio-based polyimines and nanocomposites reported here offer various advantages, including high mechanical properties and Tg, excellent thermal stability, remarkable thermal conductivity, and recyclability, which provides a new direction for the development of high-performance base composite networks.

Cyclization assisted iterative growth method for synthesizing monodisperse polymers

A fast iterative growth method is reported to prepare monodisperse polymers assisted by a cyclization technique. This novel method uses a di-functional and a tri-functional compounds as monomer pairs. The di-functional monomer is designed to have an azide and a hydroxyl end groups, while the tri-functional monomer is designed to have an alkyne and a sym-dibenzo-1,5-cyclooctadiene-3,7-diyne containing two strained alkynes. One iterative cycle of this novel method is composed by four step reactions. First, the self-accelerating double-strain-promoted azide-alkyne click reaction is used to couple two monomers/oligomers having an azide and a hydroxyl end group pairs with one tri-functional monomer by reacting the azide and strained alkyne groups. This coupling reaction increases chain length and produces an elongated oligomers having two hydroxyl end groups and one alkyne group in the middle position of main-chain. Second, the esterification between anhydride and hydroxyl is used to modify the hydroxyl end groups to endow the elongated oligomers with two azide end groups. Third, copper(I)-catalyzed azide-alkyne click reaction is then used to ring-close the elongated oligomers by reacting the middle alkyne and one terminal azide groups to prepare a tadpole-shaped oligomers with one azide end group. Fourth, the 2,3-dichloro-5,6-dicyano-p-benzoquinone oxidized deprotection reaction is used to cleave the preset methoxybenzyl ether bond in the ring of the tadpole-shaped oligomers and rebuild an azide and a hydroxyl end group pairs for the elongated oligomers. The repetition of above iterative cycle can synthesize the monodisperse polymers with a fast chain-growth manner of 2n+1-1.

Zeolite/polymer core-shell hybrid nanoparticles with hierarchical micro/meso-pores

Here, we report a new approach for preparing zeolite-polymer core-shell-like materials with hierarchical porosity via photopolymerization of trifunctional acrylic monomer (TMPTA) under UV–visible irradiation using a bifunctional Silane-based Photoinitiator (SPI-1) as coupling agent. The free radicals generated on the surface of zeolites initiate the polymerization of the diluted monomers, creating an external and mesoporous polymer shell layer. The efficiency of the photopolymerization process and the textural properties of synthesized materials are investigated using different techniques, including PXRD, TGA, UV–Vis, FTIR, SEM, and TEM. The accessibility to the pores of the zeolite core is investigated by N2 physisorption at 77 K and other probe molecules using IR spectroscopy. Interestingly, the results demonstrate a good covering of the zeolite surfaces by polymers shell. The new approach is highly repetitive and reproducible, and the accessibility to the zeolite's micropores is preserved at around 90%, which is not reported previously. The hybrid materials show higher hydrophobicity and higher ethanol adsorption capacities compared to the parent material and are potential candidates for ethanol dehydration, demonstrating a new and easy way for preparing zeolite/polymer hybrid materials for various applications such as ethanol dehydration.

Synthesis, Curing Behaviors and Properties of a Bio-Based Trifunctional Epoxy Silicone Modified Epoxy Thermosets.

Tremendous effort has been focused on improving the toughness of epoxy, but the common approaches diminish the mechanical properties. In this work, a new silicone-modified trifunctional epoxy monomer SITEUP is synthesized from the hydrosilylation transformation of eugenol epoxy (EPEU) and tris-(dimethylsiloxy)phenylsilane. The chemical structures and curing kinetics of SITEUP are investigated based on 1H-NMR, 13C-NMR, MADLI-TOF-MS, and DSC analyses. SITEUP is introduced into DGEBA/IPDA systems as a functional modifier in varied loadings for toughening the resulting epoxy thermosets. The impact strength of the modified epoxy thermosets containing 20% SITEUP is 84% higher than that of the pristine epoxy thermoset and also maintains high flexural strength. Further morphology study reveals that the plastic deformation caused by siloxane segments is the key factor accounting for the enhanced toughness of the finalized epoxy thermosets. Si-O-Si segments incorporated into the thermosetting network could absorb more energy by increasing the mobility of polymer chains under external stress and led to improved thermal stability and damping characteristics. In addition, SITEUP is able to decrease the surface tension and increase the hydrophobic properties of the resultant epoxy materials.

Structures of the co‐branching reactive products of isotactic polypropylene with high‐density polyethylene and the effect on the in situ compatibilization of mixed recycled materials

AbstractThe recycling of petroleum‐based polymers such as polypropylene (PP) and polyethylene (PE) is an effective means of reducing environmental pollution. However, the incompatible PP and PE blended waste is difficult to separate accurately, which reduces the quality of the recycled material. In this paper, the trifunctional acrylate monomer (trimethylolpropane triacrylate), peroxide (2,5‐dimethyl‐92,5‐di[tert‐butylperoxy] hexane) and free radical activity modifier (zinc dimethyldithiocarbamate) were applied to in situ generate the copolymer of isotactic polypropylene and high‐density polyethylene (iPP‐co‐HDPE) with a long‐chain co‐branched structure via a melt blending method. The co‐crystallization of the branched copolymer chain segments with the chemical identical homopolymers vastly improved the compatibility of iPP and HDPE components. This in situ co‐branching compatibility strategy resulted in a significant improvement in the mechanical properties of PE and PP mixed wastes. The temperature gradient extraction method was used to separate the co‐branching modified iPP/HDPE blends. The results confirm that the separated iPP‐co‐HDPE components have a highly co‐branched structure. The significant improvement in compatibility resulted in a large increase in elongation at break and impact strength of the iPP/HDPE blends, which provides an economic and effective method for the recycling of mixed PE and PP wastes.

Synthesis, characterization and application of soluble fully conjugated polyazomethine from di‐ or trifunctional monomers

AbstractFully conjugated polyazomethines (PAZs) exhibit large amounts of micropores among their many short branches in relatively planar structures based on their fully conjugated configuration. However, these fully conjugated structures cause insolubility and non‐processability of the PAZs because they may have strong stacking interactions due to their planar structures. In this paper, to overcome this problem, three short lengths of oligodimethylsiloxane (ODMS) grafts (x = 9, 18 and 39) were introduced by end‐capping reaction of aldehydes at the end of insoluble PAZs with amino‐terminated ODMSs as end‐capping agents. As a result, the insoluble PAZs became almost soluble (solubility > 95–100%) and their molecular weight could be estimated using gel permeation chromatography (Mw = 15.9 × 103 g mol−1). PAZ‐embedded mixed‐matrix membranes (MMMs) were fabricated using blend solutions containing only small amounts (1.0 wt%) of the solubilized PAZs with ODMS grafts and crosslinked polydimethylsiloxane (PDMS). The PAZs/PDMS MMMs showed ultrahigh permeability to oxygen which achieved 8600 barrer without a decrease of the original permselectivity of PDMS. The excellent oxygen permeability of the PAZs/PDMS MMMs may be caused by an effective increase of porosity based on the fully conjugated PAZ nanosheet. © 2022 Society of Industrial Chemistry.

Synthesis and Characterization of Chelating Hyperbranched Polyester Nanoparticles for Cd(II) Ion Removal from Water.

Chelating hyperbranched polyester (CHPE) nanoparticles have become an attractive new material family for developing high-capacity nanoscale chelating agents with highly branched structures and many functional groups in the main chains and end groups that can be used to remove heavy metals from water. In this study, a hyperbranched polyester with a particle size of 180–643 nm was synthesized with A2+B3 interfacial polymerization, using dimethylmalonyl chloride as the difunctional monomer (A2) and 1,1,1-tris(4-hydroxyphenyl)ethane (THPE) as the trifunctional monomer (B3). FTIR and NMR were used to characterize the CHPE and confirm the structure. The CHPE nanoparticles were generally considered hydrophilic, with an observed swelling capacity of 160.70%. The thermal properties of the CHPE nanoparticles were studied by thermal gravimetric analysis (TGA) with 1% mass loss at temperatures above 185 °C. The XRD of the CHPE nanoparticles showed a semi-crystalline pattern, as evident from the presence of peaks at positions ~18° and 20°. The nature of the surface of the CHPE was examined using SEM. Batch equilibrium was used to investigate the removal properties of the CHPE nanoparticles towards Cd(II) ions as a function of temperature, contact time, and Cd(II) concentration. The Cd(II) ion thermodynamics, kinetics, and desorption data on the CHPE nanoparticles were also studied.

A method to quantify composition, purity, and cross-link density of the active polyamide layer in reverse osmosis composite membranes using 13C cross polarization magic angle spinning nuclear magnetic resonance spectroscopy

A method for harvesting and purifying the thin polyamide (PA) active layer from thin-film composite (TFC) reverse osmosis (RO) membranes was developed, enabling quantitative nuclear magnetic resonance (NMR) measurements of the composition and cross-linking in the PA layer that can be directly related to membrane performance. Using our chemical separation process, we report on four trimesoyl chloride (TMC)/isophthaloyl chloride (IPC)/ m -phenylene diamine (MPD)-based TFC membranes in which the cross-link density was intentionally reduced by replacing trifunctional cross-linking TMC monomers with their linear IPC difunctional analog. While the NMR results show a two-fold decrease in cross-linking that causes a 30% increase in salt passage, the addition of the difunctional analog leads to increased polar amine groups that reduce water permeance due to tighter binding of water in the PA membrane. Our results demonstrate that 13 C cross polarization magic angle spinning (CPMAS) is a powerful method for quantitatively monitoring the purity, cross-linking, and chemical composition in PA membranes and will be an essential tool in ascertaining atomistic models of PA structure. • A method for purifying the polyamide layer from TFC RO membranes was developed. • 13 C CPMAS quantifies composition and crosslinking in harvested polyamide TFC RO films. • Crosslinking is controlled by IPC/TMC ratio. • With a two-fold decrease in crosslinking, a 30% increase in salt passage. • With a two-fold increase of amine content, a 30% decrease in water permeance.

Effect of the polymerization degree of photopolymers on the thermal and mechanical properties of ceramic cores

A ceramic core must have a high fracture strength before and after heat treatment to reasonably handle the complex and thin parts. To develop such a ceramic core, herein, a photocurable monomer with high network density was applied as an organic binder to increase green strength, and an inorganic binder was additionally introduced to minimize the shape distortion of the core due to the organic–inorganic conversion process. Fused silica beads as a starting material and trifunctional and monofunctional acrylate as an organic binder were used; these slurries with various compositions formed the green body of the core shaped through a pressing process. Next, the green body was subjected to UV irradiation for 10 min to photopolymerize the monomer, followed by heat treatment at 900 °C for 1 h to convert the inorganic binder into a glass phase and to decompose the polymer. The as-prepared ceramic core exhibited a high strength of ∼20 MPa before heat treatment owing to the presence of the crosslinked polymer with high network density. By converting the inorganic binder into a glass phase, it was possible to manufacture the ceramic core at a strength of ∼40 MPa. The photopolymerization behavior of monofunctional and trifunctional acrylate monomers and a mixture of both monomers was analyzed by FT-IR spectroscopy, and the thermal behavior of each ceramic core sample was analyzed by TG-DTA. The relationship between the polymerization degree of the photocurable monomer and strength was investigated via thermal analysis and microstructure measurement.

Polymer Stabilization of Uniform Lying Helix Texture in a Bimesogen-Doped Cholesteric Liquid Crystal for Frequency-Modulated Electro-Optic Responses.

A polymer network (PN) can sustain the uniform lying helix (ULH) texture in a binary cholesteric liquid crystal (LC) comprising a calamitic LC and a bimesogenic LC dimer. Upon copolymerization of a bifunctional monomer with a trifunctional monomer at a concentration of 5 wt% to create the desired polymer network structure, the PN-ULH was obtained with high stability and recoverability even when cycles of helical unwinding-to-rewinding processes were induced after the electrical or thermal treatment. Utilizing dielectric spectroscopy, the flexoelectric-polarization-dominated dielectric relaxation in the PN-ULH state was characterized to determine two frequency regions, f < fflexo and f > fdi, with pronounced and suppressed flexoelectric effect, respectively. It is demonstrated that the cell in the PN-ULH state can operate in the light-intensity modulation mode by the flexoelectric and dielectric effects at f < fflexo and phase-shift mode by the dielectric effect at f > fdi. Moreover, varying the voltage frequency from f < fflexo to f > fdi results in a frequency dispersion of transmittance analogous to that of flexoelectric-polarization-dominated dielectric relaxation. The unique combination of the bimesogen-doped cholesteric LC with a stable and recoverable PN-ULH texture is thus promising for developing a frequency-modulated electro-optic device.