We examine the transfer of graphene grown by chemical vapor deposition (CVD) with polymer scaffolds of poly(methyl methacrylate) (PMMA), poly(lactic acid) (PLA), poly(phthalaldehyde) (PPA), and ...poly(bisphenol A carbonate) (PC). We find that optimally reactive PC scaffolds provide the cleanest graphene transfers without any annealing, after extensive comparison with optical microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and scanning tunneling microscopy. Comparatively, films transferred with PLA, PPA, PMMA PC, and PMMA have a two-fold higher roughness and a five-fold higher chemical doping. Using PC scaffolds, we demonstrate the clean transfer of CVD multilayer graphene, fluorinated graphene, and hexagonal boron nitride. Our annealing free, PC transfers enable the use of atomically-clean nanomaterials in biomolecule encapsulation and flexible electronic applications.
End-capped poly(phthalaldehyde) (PPA) synthesized by anionic polymerization has garnered significant interest due to its ease of synthesis and rapid depolymerization. However, alternative ionic ...polymerizations to produce PPA have been largely unexplored. In this report, we demonstrate that a cationic polymerization of o-phthalaldehyde initiated by boron trifluoride results in cyclic PPA in high yield, with high molecular weight, and with extremely high cyclic purity. The cyclic structure is confirmed by NMR spectroscopy, MALDI-TOF mass spectrometry, and triple-detection GPC. The cyclic polymers are reversibly opened and closed under the polymerization conditions. Owing to PPA’s low ceiling temperature, cyclic PPA is capable of chain extension to larger molecular weights, controlled depolymerization to smaller molecular weights, or dynamic intermixing with other polymer chains, both cyclics and end-capped linears. These unusual properties endow the system with great flexibility in the synthesis and isolation of pure cyclic polymers of high molecular weight. Further, we speculate that the absence of end groups enhances the stability of cyclic PPA and makes it an attractive candidate for lithographic applications.
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IJS, KILJ, NUK, PNG, UL, UM
Biological systems rely on recyclable materials resources such as amino acids, carbohydrates and nucleic acids. When biomaterials are damaged as a result of aging or stress, tissues undergo repair by ...a depolymerization-repolymerization sequence of remodelling. Integration of this concept into synthetic materials systems may lead to devices with extended lifetimes. Here, we show that a metastable polymer, end-capped poly(o-phthalaldehyde), undergoes mechanically initiated depolymerization to revert the material to monomers. Trapping experiments and steered molecular dynamics simulations are consistent with a heterolytic scission mechanism. The obtained monomer was repolymerized by a chemical initiator, effectively completing a depolymerization-repolymerization cycle. By emulating remodelling of biomaterials, this model system suggests the possibility of smart materials where aging or mechanical damage triggers depolymerization, and orthogonal conditions regenerate the polymer when and where necessary.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Triggerable transient electronics are demonstrated with the use of a metastable poly(phthalaldehyde) polymer substrate and encapsulant. The rate of degradation is controlled by the concentration of ...the photo‐acid generator and UV irradiance. This work expands on the materials that can be used for transient electronics by demonstrating transience in response to a preselected trigger without the need for solution‐based degradation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Thermally triggered transient electronics using wax‐encapsulated acid, which enable rapid device destruction via acidic degradation of the metal electronic components are reported. Using a cyclic ...poly(phthalaldehyde) (cPPA) substrate affords a more rapid destruction of the device due to acidic depolymerization of cPPA.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
End-capped poly(phthalaldehyde) PPA is a well-studied metastable polymer that has attracted interest due to its ease of synthesis and rapid depolymerization. PPA is limited, however, in the type of ...macromolecular architectures accessible, as functionalizable phthalaldehyde derivatives are not commercially available and their synthesis is cumbersome. To this end, a general route to phthalaldehyde–benzaldehyde copolymers was sought, as benzaldehyde comonomers with various pendant functionalities are readily available. It was found that copolymers are synthesized by an anionic initiated polymerization of phthalaldehyde and electron-deficient benzaldehydes. The comonomer reactivities are shown to be sensitive to the benzaldehyde electronics; the relative reactivity of phthalaldehyde–benzaldehyde comonomer pairs strongly correlate with the Hammett values of the benzaldehyde monomer. These copolymers are then further modified to yield cross-linked, degradable polymer networks in just a two-step sequence. Phthalaldehyde–benzaldehyde copolymers thus enable functionalization of metastable polymers that rapidly depolymerize upon exposure to acid, thereby facilitating the development of triggerable degradation of polymer networks.
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IJS, KILJ, NUK, PNG, UL, UM
Aldehyde polymers have gained attention in recent decades as a class of stimuli-responsive materials capable of rapid, triggered depolymerization to monomer. Exploitation of the most prominent ...polyaldehydes for various solid-state applications, however, is limited by poor thermal and mechanical properties of the materials. To address these limitations, we pursued the copolymerization of ethyl glyoxylate, precursor to tacky polymers, with o-phthalaldehyde, precursor to brittle materials. Using NMR spectroscopy and MALDI-TOF mass spectrometry, we have discovered the surprising tendency of these sequences to alternate, resulting in alternating cyclic copolymers in certain feed ratios. We also report the ability to tailor the thermal properties of the solid copolymers by varying copolymer composition, enabling the selective tuning of copolymer glass transition and degradation temperatures to meet application demands. We envision that this copolymer system, which blends the properties of the tacky and brittle homopolymers, will find use as depolymerizable polyaldehydes for solid-state applications.
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We recently discovered that the cationic polymerization of o-phthalaldehyde generates cyclic poly(phthalaldehyde) in high yield, high molecular weight, and a high degree of cyclic purity. Given this ...surprising result, we pursued the cationic polymerization of ethyl glyoxylate to determine if the macrocyclization outcome is, in fact, a general trend of low ceiling temperature polyacetals. Using NMR spectroscopy, MALDI-TOF mass spectrometry, and triple detection GPC, we have uncovered divergent macrocyclization mechanisms in the cationic polymerization of ethyl glyoxylate. Backbiting is observed either via the backbone acetal or via the pendant ester to give disparate polymer products and unique polymer architectures. The favored route for cyclization is found to depend on both the monomer concentration and the initiating species. Understanding the underlying mechanisms of polymerization and the ability to rigorously control polymer structure has important implications for the design of new transient materials.
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Photoresponsive polymers capable of luminescence switching are attracting significant interest due to their potential application in fluorescence patterning, bioimaging, optical data storage, and ...anti-counterfeiting. In this work, we have developed aqueous-soluble copolymers of 1-naphthyl methacrylate and oligo(ethylene glycol) methyl ether methacrylate P(1-NMA-co-OEGMA) that undergo a significant shift in fluorescence emission wavelength after UV irradiation. Irradiation of the 1-naphthyl methacrylate moieties results in the photo-Fries rearrangement to form hydroxy aryl ketones, which exhibit strong emission at 475 nm through excited-state intramolecular proton transfer (ESIPT) and excited-state proton transfer (ESPT). The resultant shift in fluorescence emission maximum from 338 to 475 nm after rearrangement can potentially be exploited for fluorescence patterning. Furthermore, the copolymers are thermally sensitive in aqueous solutions. The lower critical solution temperature (LCST) of the copolymers depends on the content of hydrophobic 1-naphthyl methacrylate units; the photo-Fries rearrangement results in a more polar structure, shifting the LCST to a higher temperature. Of note, the temperature-triggered volume phase transition of copolymer hydrogels selectively ″switches off″ fluorescence arising from the ESPT mechanism, while the ESIPT emission is unaffected. We also demonstrate that films formed by coating the copolymers onto various substrates can be selectively patterned to form gradients in fluorescence intensity. These versatile P(1-NMA-co-OEGMA) copolymers are simple to prepare at low cost, demonstrate effective photoswitching, and have excellent water solubility, thus ensuring potential applications in a number of important areas.
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IJS, KILJ, NUK, PNG, UL, UM
We recently reported the cationic polymerization of o-phthalaldehyde to macrocyclic poly(phthalaldehyde) polymers. Resubjecting the cyclic polymers to the polymerization conditions led to a ...redistribution of the polymer to a new cyclic structure consistent with thermodynamic equilibrium. We now report the synthesis of cyclic poly(phthalaldehyde) derivatives and demonstrate the scrambling of distinct homopolymer mixtures to copolymers under the cationic polymerization conditions. Homopolymer mixtures are found to rapidly redistribute, first to multiblock cyclic copolymers. With extended reaction time, random macrocyclic copolymers are obtained. Evolution of the microstructure was monitored by NMR spectroscopy, MALDI–TOF mass spectrometry, and gel permeation chromatography (GPC). The reported scrambling method leads to the rapid preparation of macrocyclic copolymers of high molecular weight with variable microstructure depending on reaction times and catalyst loadings.
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