[ CAS No. 121239-75-6 ] (4-(Octyloxy)phenyl)(phenyl)iodonium hexafluorostibate(V)

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Abstract: UV-induced frontal polymerization is an emergent rapid curing method for thermoset resin and its fiber composites which features the generation of a self-sustaining front that propagates within the entire material. This is different from using the commercially available UV curable resin which prohibited the curing of thermoset composites with opaque fibers (e.g., carbon fiber) due to the UV light being blocked by the fibers. In this study, we experimentally demonstrate that using the UV-induced frontal polymerization allows us to reduce the curing time of a standard tensile specimen of epoxy resin from traditionally 15 h using the oven curing method to only less than 1.5 min. The frontal polymerized epoxy specimens showed comparable and even superior tensile and flexural properties when compared to the traditional oven cured specimens. Moreover, we experimentally investigated the influence of the weight content of the photoinitiator, the UV light intensity, and the specimen geometry on the characteristics of the frontal polymerization process (i.e., front temperature, front velocity, and degree of cure) and the resulting tensile and flexural properties. The results and discussions are expected to provide guidance in scaling up this UV-induced frontal polymerization technique for the sustainable and additive manufacturing and repair of thermoset resin and its fiber composites.

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Abstract: Frontal polymerization is a process in which a localized reaction zone propagates through the coupling of thermal transport and the Arrhenius kinetics of exothermic polymerization. Most initiators that have been used produce volatile by-products, which create bubbles and voids. Tetraalkyl ammonium persulfates have been used but these require synthesis and do not have long shelf lives. A charge transfer complex (CTC) composed of an iodonium salt, and a phosphine compound has been identified as a gas-free initiator for free-radical thermal frontal polymerization. This CTC has 4-(dimethylamino)phenyldiphenly phophine (DMAPDP) as the donor and p-(octyloxyphenyl)phenyliodonium hexafluoroantimonate as the acceptor (IOC-8). The CTC was tested with several acrylates, and all were found to support bubble-free fronts. We determined the CTC mole ratio for some monomers at which the front velocity reaches a plateau.

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Abstract: Addition of fillers to formulations can generate composites with improved mechanical properties and lower the overall cost through a reduction of chemicals needed. In this study, fillers were added to resin systems consisting of epoxies and vinyl ethers that frontally polymerized through a radical-induced cationic frontal polymerization (RICFP) mechanism. Different clays, along with inert fumed silica, were added to increase the viscosity and reduce the convection, results of which did not follow many trends present in free-radical frontal polymerization. The clays were found to reduce the front velocity of RICFP systems overall compared to systems with only fumed silica. It is hypothesized that chemical effects and water content produce this reduction when clays are added to the cationic system. Mechanical and thermal properties of composites were studied, along with filler dispersion in the cured material. Drying the clays in an oven increased the front velocity. Comparing thermally insulating wood flour to thermally conducting carbon fibers, we observed that the carbon fibers resulted in an increase in front velocity, while the wood flour reduced the front velocity. Finally, it was shown that acid-treated montmorillonite K10 polymerizes RICFP systems containing vinyl ether even in the absence of an initiator, resulting in a short pot life.

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Abstract: Ultrahigh-density displays are becoming increasingly prevalent in display technology for immersive digital interactive devices. However, the pursuit of higher pixel resolution has inadvertently led to the emergence of electrical pixel crosstalk, primarily due to the use of common hole transporting layers (HTLs). In this work, we present wafer-scale, anti-pixel crosstalk micro-lithography to mitigate electrical pixel crosstalk by incorporating a silicone-integrated small molecule HTL (SI-HTL), which not only enables ultrahigh-density pixelation but also enhances the functionality of the HTL itself. Leveraging the inherent silicon etching properties of SI-HTL, we successfully created high-fidelity micro-pattern arrays with a remarkable resolution of up to 10,062 pixels per inch on 6-inch wafer scales. Furthermore, SI-HTL effectively modulates charge balance within the emission layers, resulting in improved luminance characteristics in organic light-emitting diodes (OLEDs). Our comprehensive optical and quantitative assessment of electrical pixel crosstalk in OLEDs integrated with micro-patterned SI-HTL demonstrates the significant effectiveness of high pixelation of the HTL in alleviating the crosstalk issue.

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Abstract: Radical induced cationic frontal polymerization (RICFP) is a promising route to achieve rapid curing of epoxy-based thermosets, requiring only a localized exposure with UV light. In the presence of a diaryliodonium-based photoinitiator and a thermal radical initiator, a self-sustaining hot front cures epoxide monomer via a cationic mechanism. However, the cationic polymerization of diglycidyl ether derivatives is slow (in comparison with other epoxides with higher reactivity) and, as a consequence, frontal polymerization is sluggish because the heat loss is not compensated by the rate of heat release. Cycloaliphatic epoxies possess a higher ring strain than diglycidyl ether derivatives and can be blended with the latter to increase its rate of frontal polymerization. In the current work, a comprehensive study on the influence of 3,4 epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (CE) on cure kinetics, viscosity, front velocity, mechanical, and thermo-mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives is presented. The results show a direct relationship between frontal velocity and amount of reactive diluent while an inverse relationship with the storage viscosity is observed. It is found that increasing the content of cycloaliphatic epoxide reduces the glass transition but increases mechanical properties of frontally cured bisphenol A diglycidyl ether derivatives.

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Abstract: Frontal polymerization is a process in which a localized reaction zone propagates from the coupling of thermal transport and the Arrhenius rate dependence of an exothermic polymerization; monomer is converted into polymer as the front passes through an unstirred medium. Herein we report the first study of charge transfer complexes (CTCs) as photo/thermal initiators for free-radical frontal polymerization. Front velocity was studied as a function of mole ratio between an aromatic amine, such as dimethyl-p-toluidine or dimethylaniline, and an iodonium salt. It was found that the front velocity reached a maximum at a certain mole ratio of amine to iodonium salt. The velocity remained constant upon increasing the ratio of amine to iodonium salt past this critical ratio. Fronts were also studied using N-phenyl glycine as an electron donor, but its utility was limited by low solubility. Lastly, the steric and electronic effects of the iodonium salt and counter anion were explored. It was found that CTCs using iodonium salts with less nucleophilic anions gave higher front velocities. In terms of intrinsic reactivity, the CTC composed of N,N-dimethyl-p-toluidine and bis[4-(tert-butyl)phenyl]iodonium tetra(nonafluoro-tert-butoxy)aluminate gave the highest front velocity per molal of iodonium salt.

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Abstract: With additive manufacturing, it is now possible to repeatedly create 3D objects without the need for molds or heavy machining. In comparison with other additive manufacturing techniques, vat photopolymerization provides a fast and precise way of producing complex shapes and objects. Photopolymerization 3D printing uses light exposure to solidify a resin formulation and is typically limited to a single material. In recent years, researchers have focused on using multi-material 3D printing to manufacture objects with heterogeneous properties. A promising approach for vat photopolymerization 3D printing of multi-material objects is the use of orthogonal photoreactions to tailor the network properties. In this work, three different hybrid acrylate-epoxide systems were formulated to present the possibility of preparing dual-curable resins for 3D printing, and tuning their properties using dual-wavelength DLP 3D printing technology: a) DOM:ECC = 75:25, 25:75 b) Eb:ECC = 25:75 c) PEGDA:ECC = 50:50 The 3D printer used in this work, employs two different light engines, operating at 405 and 365 nm. At visible light irradiation, a radical photoinitiator was selectively activated, leading to the curing of the acrylate component. Upon UV light exposure, a radical curing as well as cationic ring opening process of the epoxide component was initiated, yielding an interpenetrating network (IPN) with higher crosslinking density and stiffness. For the quantitative conversion of the epoxide network, a thermal post-baking step was carried out at 120°C for 2 hours. The cure kinetics of prepared hybrid acrylate-epoxide resins were investigated using the FTIR spectroscopy and through the initial printing trials. Selective illumination with either light source should shift material properties between the soft acrylate and rather stiff epoxide network. This was verified for DOM:ECC and PEGDA:ECC systems, while the system Eb:ECC displayed thermal instability and inability to print wavelength selective materials. The system Eb:ECC was not subjected to further testing. Furthermore, to investigate mechanical behavior of the printed samples, dynamical mechanical analysis and tensile test were carried out.