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Perfluorocyclobutane (PFCB) polymer solutions were subjected to pulsed ultrasound, leading to mechanically induced chain scission and molecular weight degradation. 19F NMR revealed that the new, mechanically generated end groups are trifluorovinyl ethers formed by cycloreversion of the PFCB groups, a process that differs from thermal degradation pathways. One consequence of the mechanochemical process is that the trifluorovinyl ether end groups can be remended simply by subjecting the polymer solution to the original polymerization conditions, that is, heating to >150 °C. Stereochemical changes in the PFCBs, in combination with radical trapping experiments, indicate that PFCB scission proceeds via a stepwise mechanism with a 1,4-diradical intermediate, offering a potential mechanism for localized functionalization and cross-linking in regions of high stress.

The spontaneous conversion of a flat film into a 3-D shape requires local programming of the mechanical response. Historically, the ability to locally program the mechanical response of high strain (>30%) liquid crystalline elastomers (LCEs) has been limited to magnetic or mechanical alignment techniques, which limits spatial resolution. Recently, we reported on the preparation of LCEs capable of 55% strain with spatial control of the mechanical response at scales as small as 0.01 mm 2 . Here, we report a distinct formulation strategy to realize programmable stimulus-response in LCEs. Photopolymerization of thiol−ene/acrylate formulations yields materials that exhibit large reversible strain up to 150%. The photopolymerization reaction is extremely rapid, reducing preparation time from days to minutes. The mechanical behavior of these materials can be tuned by varying cross-link density. Spatial and hierarchical programming of the director profile is demonstrated, enabling 3-D shape change, including twisting ribbons and localized Gaussian curvature. M aterials capable of reversibly changing shape have the potential to enable simple mechanical devices, where traditional mechanical elements are difficult to employ. 1 Such materials are often categorized by the magnitude and complexity of achievable shape change in response to a given stimulus. Through patterning, it has been demonstrated that hydrogels, semicrystalline polymers, and liquid crystal networks can be designed to undergo complex shape change in response to solvents, light, and heat. 2−4 Complex shape change in monolithic materials is achieved through spatial and hierarchical control of the magnitude or direction of stimuli-response. In ordered materials this can be achieved through spatial control of molecular orientation.The polymerization of liquid crystalline monomers can retain the order within an elastic solid. 5 In uniaxially aligned liquid crystalline elastomers (LCEs), lightly cross-linked networks, reversible strains greater than 300% have been reported. 6 Oriented LCEs have typically been aligned by mechanical loading or magnetic fields, which can generate films with uniaxial or relatively simple patterns. 7,8 In densely cross-linked liquid crystal polymers, surface alignment techniques, such as rubbing or photoalignment, have been employed to prepare ordered polymer networks with comparatively complex local alignment. 9 Recently, main-chain LCEs that are amenable to photoalignment have been demonstrated, allowing for arbitrary spatial alignment of the nematic director over regions as small as 0.01 mm 2 . 10 Key to the realization of this material was the use of a two-step synthesis, comprised of the Michael addition of a nematic diacrylate to a primary amine followed by subsequent cross-linking of the telechelic diacrylate oligomer, which results in a LCE that exhibits maximum strains of 55%. 11 Critically, this reaction scheme can proceed in one-pot (a liquid crystal cell), exhibits a wide nematic phase window, and proceeds without the ad...

This article highlights the preparation of perfluorocyclobutyl (PFCB) aryl ether polymers for a multitude of commercial technologies that are of academic and commercial global interest. In this account, the synthesis of various aryl trifluorovinyl ether (TFVE) monomers tailored for specific applications is

Two new fluorinated diamine-based benzoxazines using octafluorocyclopentene (OFCP) as a building block have been developed. Monomers were synthesized via two distinct synthetic procedures utilizing the facile nucleophilic addition−elimination reaction of OFCP with phenols amenable to a multigram scale-up. The structure elucidation of both monomers was confirmed by 1 H, 19 F, and 13 C NMR, ATR-FTIR, and high-resolution mass spectrometry. Benzoxazine networks were prepared by a thermally mediated ring-opening polymerization. ATR-FTIR analysis was utilized to monitor the ring-opening reaction of the monomers. The resulting two cured resins exhibit the combined excellent properties of low dielectric constants (k = 3.2−2.6), excellent thermal stability, and high char yields which are suitable for many applications such as flame-resistant materials as well as aerospace and microelectronic industries.

New fluorinated polyhedral oligomeric silsesquioxane (F-POSS) structures possessing a high degree of hydrophobicity have been prepared via a facile corner-capping methodology.

Aluminum (Al) particles are passivated by an aluminum oxide (Al2O3) shell. Energetic blends of nanometer-sized Al particles with liquid perfluorocarbon-based oxidizers such as perfluoropolyethers (PFPE) excite surface exothermic reaction between fluorine and the Al2O3 shell. The surface reaction promotes Al particle reactivity. Many Al-fueled composites use solid oxidizers that induce no Al2O3 surface exothermicity, such as molybdenum trioxide (MoO3) or copper oxide (CuO). This study investigates a perfluorinated polymer additive, PFPE, incorporated to activate Al reactivity in Al-CuO and Al-MoO3. Flame speeds, differential scanning calorimetry (DSC), and quadrupole mass spectrometry (QMS) were performed for varying percentages of PFPE blended with Al/MoO3 or Al/CuO to examine reaction kinetics and combustion performance. X-ray photoelectron spectroscopy (XPS) was performed to identify product species. Results show that the performance of the thermite-PFPE blends is highly dependent on the bond dissociation energy of the metal oxide. Fluorine-Al-based surface reaction with MoO3 produces an increase in reactivity, whereas the blends with CuO show a decline when the PFPE concentration is increased. These results provide new evidence that optimizing Al combustion can be achieved through activating exothermic Al surface reactions.

Metastable composites were prepared from a fl uoropolymer-coated nano-aluminum blended formulation entrained in an epoxy matrix. This composition produced a moldable/post-machinable composite that undergoes thermally activated metal-mediated oxidation. The simplistic, scalable design can warrant consideration for a new class of engineered metal-based fl uoropolymer pyrolant composite systems. As featured in:See S. Fluoropolymers have long served as potent oxidizers for metal-based pyrolant designs for the preparation of energetic materials. Commercial perfluoropolyethers (PFPEs), specifically known as FomblinsÒ, are wellknown to undergo accelerated thermal degradation in the presence of native metals and Lewis acids producing energetically favorable metal fluoride species. This study employs the use of PFPEs to coat nano-aluminum (n-Al) and under optimized stoichiometric formulations, harness optimized energy output. The PFPEs serve as ideal oxidizers of n-Al because they are non-volatile, viscous liquids that coat the particles thereby maximizing surface interactions. The n-Al/PFPE blended combination is required to interface with an epoxy-based matrix in order to engineer a moldable/machinable, structurally viable epoxy composite without compromising bulk thermal/mechanical properties. Computational modeling/ simulation supported by thermal experimental studies showed that the n-Al/PFPE blended epoxy composites produced an energetic material that undergoes latent thermal metal-mediated oxidation.Details of the work include the operationally simple, scalable synthetic preparation, thermal properties from DSC/TGA, and SEM/TEM of these energetic metallized nanocomposite systems. Post-burn analysis using powder XRD of this pyrolant system confirms the presence of the predominating exothermic metal-mediated oxidized AlF 3 species in addition to the production of Al 2 O 3 and Al 4 C 3 during the deflagration reaction. Details of this first epoxy-based energetic nanocomposite entrained with a thermally reactive formulation of PFPE coated n-Al particles are presented herein.