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Abstract Applications in soft, flexible optical, and optoelectronic applications demand polymer thin film coatings that can accommodate substantial physical deformations. The preparation of high refractive index polymers (HRIPs) through the quaternization of poly(4‐vinylpyridine) (P4VP) thin films with (di)halomethanes is presented. P4VP thin films are prepared by initiated chemical vapor deposition (iCVD) and then quaternized through exposure to saturated vapors of iodomethane (CH₃I), dibromomethane (CH₂Br₂), and diiodomethane (CH₂I₂), resulting in refractive indices (RI) as high as 1.67, 1.71, and 2.07, respectively (at 632.8 nm). Fourier‐transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) confirmed the quaternization of pyridine pendant groups on the polymer chain to n‐methylpyridinium with primarily an iodide or bromide counterion, though a minor fraction of polyiodides are also detected. Additionally, these films demonstrate superior thermal stability, retaining their refractive index and thickness after thermal excursions to 200 °C. The halogenated P4VP films exhibit superior mechanical flexibility relative to conventional inorganic coatings (Al₂O₃and Ta₂O₅) and do not fracture at uniaxial tensile strains as high as 10%. This new material chemistry and fabrication approach method may enable advanced optical designs and functionality in a wide range of substrates and device architectures. 

Abstract Flexible, compliant permeation barrier layers are critically needed in the optics/optoelectronics industry to protect deformable, polymer‐based optical elements, such as those found in variable focus lenses. To address these needs, a transparent and deformable polymeric permeation barrier coating consisting of poly(1H,1H,6H,6H‐perfluorohexyl diacrylate) (pPFHDA) is prepared by initiated chemical vapor deposition. pPFHDA is a highly crosslinked fluoropolymer, which is deposited onto temperature‐sensitive elastomeric membranes at ambient temperature with high uniformity and conformality. This is believed to be the first demonstration of vapor deposition of the PFHDA monomer. Coatings with thicknesses nominally ranging from 200 to 750 nm are prepared and shown to be impermeable to high‐index optical fluid (polyphenyl thioether) over 2 months at 70 °C, which translates to more than 4 year lifespan at room temperature, even after being subjected to 0.26% biaxial strain. Moreover, due to its amorphous nature, the pPFHDA is transparent from wavelengths of 300–1690 nm and also thermally stable to temperatures of 300 °C. These properties should make pPFHDA coating a particularly compelling candidate for flexible optical/optoelectronic devices requiring transparent and compliant barrier layers. 

Flexible optics and optoelectronic devices require stretchable and compliant antireflection coatings (ARC). Conventional optical coatings, typically inorganic thin films, are brittle and crack under strain, while porous or patterned surfaces often lack environmental endurance and/or involve complex processing. Polymeric optical thin films prepared by initiated chemical vapor deposition (iCVD) comprise a promising alternative class of materials. With iCVD, multilayered, uniform thin film coatings can be synthesized conformally on the surface of a temperature-sensitive substrate near room temperature with precise compositional and thickness control. In this study, a model two-layer coating design consisting of poly(1 H ,1 H ,6 H ,6 H -perfluorohexyl diacrylate) (pPFHDA) with a refractive index at 633 nm of n 633 = 1.426 was deposited atop poly(4-vinylpyridine) (p4VP, n 633 = 1.587). Broadband antireflection over the visible wavelength range (400–750 nm) was conferred to a transparent, flexible thermoplastic polyurethane (TPU) substrate ( n 633 ∼ 1.51), reducing the front-surface reflectance from ∼4% to ∼2%. The superior mechanical compliance of polymer ARCs over conventional inorganic coatings (MgF 2 , SiO 2 , and Al 2 O 3 ) on the TPU substrate was thoroughly investigated by monitoring the evolution of film morphology and tensile fracture with applied equibiaxial strain. The polymer ARC withstood at least ε = 1.64% equibiaxial strain without fracture, while all inorganic coatings cracked. Through a repeated application of strain over hundreds of cycles, the antireflection by the polymer film was shown to possess excellent stability and fatigue resilience. Finally, simulations of established iCVD polymer chemistries possessing larger index contrast revealed that reflectance can be further reduced to <1% or better. 

Conventional lithium ion battery separators are microporous polyolefin membranes that play a passive role in the electrochemical cell. Next generation separators should offer significant performance enhancements, while being fabricated through facile, low cost approaches with the ability to readily tune physicochemical properties. This study presents a single-step manufacturing technique based on UV-initiated polymerization-induced phase separation (PIPS), wherein microporous separators are fabricated from multifunctional monomers and ethylene carbonate (EC), which functions as both the pore-forming agent (porogen) and electrolyte component in the electrochemical cell. By controlling the ratio of the 1,4-butanediol diacrylate (BDDA) monomer to ethylene carbonate, monolithic microporous membranes are readily prepared with 25 μm thickness and pore sizes and porosities ranging from 6.8 to 22 nm and 15.4% to 38.5%, respectively. With 38.5% apparent porosity and an average pore size of 22 nm, the poly(1,4-butanediol diacrylate) (pBDDA) separator takes up 127% liquid electrolyte, resulting in an ionic conductivity of 1.98 mS cm −1 , which is greater than in conventional Celgard 2500. Lithium ion battery half cells consisting of LiNi 0.5 Mn 0.3 Co 0.2 O 2 cathodes and pBDDA separators were shown to undergo reversible charge/discharge cycling with an average discharge capacity of 142 mA h g −1 and a capacity retention of 98.4% over 100 cycles – comparable to cells using state-of-the-art separators. Moreover, similar discharge capacities were achieved in rate performance tests due to the high ionic conductivity and electrolyte uptake of the film. The pBDDA separators were shown to be thermally stable to 374 °C, lack low temperature thermal transitions that can compromise cell safety, and exhibit no thermal shrinkage up to 150 °C. 

Organic cathode materials have attracted significant research attention recently, yet their low electronic conductivity limits their application as solid-state cathodes in lithium batteries. This work describes the development of a novel organic cathode chemistry with significant intrinsic electronic conductivity for solid-state thin film batteries. A polymeric charge transfer complex (CTC) cathode, poly(4-vinylpyridine)-iodine monochloride (P4VP·ICl), was prepared by initiated chemical vapor deposition (iCVD). Critical chemical, physical, and electrochemical properties of the CTC complex were characterized. The complex was found to have an electronic conductivity of 4 × 10-7 S cm-1 and total conductivity of 2 × 10−6 S cm−1 at room temperature, which allows the construction of a 2.7 μm thick dense cathode. By fabricating a P4VP·ICl|LIPON|Li thin film battery, the discharge capacity of P4VP·ICl was demonstrated to be >320 mA h cm−3 on both rigid and flexible substrates. The flexible P4VP·ICl|LIPON|Li battery was prepared by simply replacing the rigid substrate with a flexible polyimide substrate and the as-prepared battery can be bent 180° while maintaining electrochemical performance.