Highly Refractive Polyimides Derived from Efficient Catalyst-Free Thiol–Yne Click Polymerization

Innocuous solvent-based, low-temperature curable, and highly transparent photosensitive polyimides developed using soluble polyimides containing bio-based magnolol moieties

Traditional photosensitive polyimide (PSPI) materials require a high curing temperature and exhibit low transparency, limiting their applications in thermally sensitive optical devices. To overcome this challenge, soluble photosensitive polyimide resins were synthesized based on the structural design of a bio-based magnolol monomer. It is noteworthy that the PI photoresist, developed by using the as-prepared polyimides and non-toxic solvents (2-acetoxy-1-methoxypropane, PGEMA) and other additives, demonstrated an impressive low-temperature curing performance (180 °C). Furthermore, the solvent residue in the cured film prepared using PGEMA as solvent was markedly decreased compared to that prepared using N-methyl pyrrolidone (NMP). In addition, the C-PI-3 films cured by photoinitiated thiol-ene radical reactions exhibited high transparency with an average visible light transmittance of 87.8%, as well as excellent thermal stability, dielectric and breakdown properties, and photo-patterning capabilities. This partially bio-based and innocuous solvent-based PSPI with low-temperature curability and high transparency properties could be a pioneering example to resolve the challenges of energy efficiency and environmental sustainability and is expected to be used in the field of color filters.

Sodium Thiophenolate Initiated Polymerization of Methacrylate with Sulfur (S8): High-Refractive-Index and -Transparency Polymers for Lithography

A simple and effective strategy for introducing sulfur into a polymethacrylate matrix at room temperature has been developed, allowing for the polymerization of a variety of methacrylate derivatives with sulfur. The resulting S-containing polymers exhibited a high refractive index of up to 1.72 while retaining over 90% transmittance in the visible region. Additionally, when mixed with 3% photo acid generator (PAG) as photoresist, the formulation demonstrated excellent patterning capabilities. Furthermore, the scalable preparation of high-refractive-index polymers (HRIPs) indicates significant potential for fabrication.

Fluorescent robust photoactuator via photo-crosslinking induced single-layered janus polyimide

Advanced smart polymer materials with the ability of reversible deformation under external stimuli hold great potential in robotics, soft machines, and flexible electronics. However, the complexity and low efficiency for fabricating actuators along with their limited functionality hinder further progress. Here an efficient and mild catalyst-free thiol-yne click polymerization was developed to fabricate photosensitive polyimide (PI) films. Then the fluorescent robust photoactuators with single-layered janus structure were directly obtained via UV assisted photo-crosslinking of the films, exhibiting reversible response driven by a pronounced mismatch in expansion between the front and back sides of the films. Achieving selective, non-uniform spatial distribution within the PI films, rapid and reversible complex morphing of the actuators, along with the capabilities for encrypting, reading, and erasing fluorescent information-all through the use of a single UV light source-becomes straightforward. The robust mechanical property and driving ability of these actuators enable the conversion of light energy into obvious motion even under heavy loads and the leaping through the storage and release of energy, ensuring their potential for practical applications that require durability and reliability.

High-Refractive-Index Cross-Linked Cyclic Olefin Polymers with Excellent Transparency via Thiol-Ene Click Reaction

High-refractive-index polymers are important optical materials in optoelectronics. Conventional cyclic olefin polymers (COPs), possessing many excellent optical properties, are a class of highly promising optical materials; however, one of the greatest obstacles is their low refractive index of n = 1.52-1.54. Here, one efficient strategy of first incorporating high molar refraction groups, including carbazolyl and indolyl moieties, into unsaturated COPs via ring-opening metathesis polymerization (ROMP) and then introducing another high molar refraction sulfur atom by a subsequent thiol-ene click reaction is presented. The obtained cross-linked COPs bearing both an aromatic group and sulfur possess significantly higher refractive indices (n = 1.611-1.684 at 589 nm) and highly optical transparency (approximately 95%) in the range of vis-NIR. This provides a way toward potential applications of new-generation optical materials.

Thiol-yne chemistry of diferrocenylacetylene: from synthesis and electrochemistry to theoretical studies

The thiol-yne coupling chemistry of diferrocenylacetylene (FcCCFc) 1, bearing two electron rich and redox-active ferrocenyl units (Fc = Fe(η⁵-C₅H₄)(η⁵-C₅H₅)) and an internal triple bond, has been investigated for the first time. In order to determine whether steric limitations might affect hydrothiolation, a model reaction using a functionalized monothiol was tested, namely 2-mercaptoethanol I. The thiol-diferrocenylacetylene reactions were initiated either thermally (in toluene with AIBN) or by UV light irradiation (in THF and in the presence of DMPA as the photoinitiator). The outcomes of these thiol-yne reactions showed a strong dependence on the initiation method used, with the thermally initiated one being the most efficient. These thiol-diferrocenylacetylene reactions mainly afforded the (Z)-stereoisomer of the newly obtained vinyl thioether sulfide FcCHC(Fc)S-(CH₂)₂OH (2), unlike the more common (E)-vinyl sulfides found in other additions to alkynes. The hydrothiolation of the internal -CC- bond in 1 was successfully extended to dithiol 2,2'-(ethylenedioxy)diethanethiol II, leading to the formation of the (ZZ)-isomer, with four ferrocenyl units, as the major product. According to the electrochemical studies, the new asymmetrical ferrocenyl-vinyl sulfides show iron-iron electronic and electrostatic interactions. Theoretical results for the (Z)-stereoisomer (2) suggest that adiabatic oxidation would lead to the loss of almost one electron on the ferrocenyl subunit closer to the thioether chain. Furthermore, the thiol-yne chemistry of the internal -CC- bond in diferrocenylacetylene has been compared to the external triple bond in ethynylferrocene, the theoretical results of which helped us to rationalize the very different reactivities observed in both metallocenes.

Polyimide Hybrid Nanocomposites with Controlled Polymer Filling and Polymer-Matrix Interaction

Polyimide hybrid nanocomposites with the polyimide confined at molecular length scales exhibit enhanced fracture resistance with excellent thermal-oxidative stability at low density. Previously, polyimide nanocomposites were fabricated by infiltration of a polyimide precursor into a nanoporous matrix followed by sequential thermally induced imidization and cross-linking of the polyimide under nanometer-scale confinement. However, byproducts formed during imidization became volatile at the cross-linking temperature, limiting the polymer fill level and degrading the nanocomposite fracture resistance. This is solved in the present work with an easier approach where the nanoporous matrix is filled with shorter preimidized polyimide chains that are cross-linked while in the pores to eliminate the need for confined imidization reactions, which produces better results compared to the previous study. In addition, we selected a preimidized polyimide that has a higher chain mobility and a stronger interaction with the matrix pore surface. Consequently, the toughness achieved with un-cross-linked preimidized polyimide chains in this work is equivalent to that achieved with the cross-linking of the previously used polyimide chains and is doubled when preimidized polyimide chains are cross-linked. The increased chain mobility enables more efficient polymer filling and higher polymer fill levels. The higher polymer-pore surface interaction increases the energy dissipation during polyimide molecular bridging, increasing the nanocomposite fracture resistance. The combination of the higher polymer fill and the stronger polymer-surface interaction is shown to provide significant improvements to the nanocomposite fracture resistance and is validated with a molecular bridging model.

Click Synthesis Enabled Sulfur Atom Strategy for Polymerization-Enhanced and Two-Photon Photosensitization

Facile tailoring of photosensitizers (PSs) with advanced and synergetic properties is highly expected to broaden and deepen photodynamic therapy (PDT) applications. Herein, a catalyst-free thiol-yne click reaction was employed to develop the sulfur atom-based PSs by using the in situ formed sulfur "heavy atom effect" to enhance the intersystem crossing (ISC), while such an effect can be remarkably magnified by the polymerization. The introduction of a tetraphenylpyrazine-based aggregation-induced emission (AIE) unit was also advantageous in PS design by suppressing their non-radiative decay to facilitate the ISC in the aggregated state. Besides, the resulting sulfur atom electron donor, together with a double-bond π bridge and AIE electron acceptor, created a donor-π-acceptor (D-π-A) molecular system with good two-photon excitation properties. Combined with the high singlet oxygen generation efficiency, the fabricated polymer nanoparticles exhibited an excellent in vitro two-photon-excited PDT towards cancer cells, therefore possessing a huge potential for the deep-tissue disease therapy.