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.

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.

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.

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.

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, 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. * Correspondence should be addressed to lyding@illinois.edu and epop@stanford.edu. Cu has proven the most fruitful platform for large-area graphene growth, as the low carbon solubility promotes monolayer growth. 8 Nevertheless, most applications using CVD-grown graphene require that the films be transferred to insulating substrates. The predominant graphene transfer approach is by using a poly(methyl methacrylate) (PMMA) scaffold. [12][13][14][15][16][17] In this method, the PMMA polymer coats the graphene, supporting it during Cu removal, underside contaminant cleaning, and placement on its destination substrate. 18, 19 However, PMMA removal from graphene after film transfer has proven challenging. 15 Approaches to remove it by high-temperature Ar/H2 forming gas annealing, 14, 20, 21 O2 based annealing, 15, 22, 23 and in situ annealing 16, 24, 25 have been marginally successful in removing PMMA without affecting the graphene. Furthermore, these processes are all at high-temperature, excluding graphene applications with low thermal budgets, including uses in flexible electronics and biomolecule encapsulation. Another process separated the graphene from the PMMA support by an Au interfacial layer, 26 but that process is subject to effective interfacial Au-graphene wetting. Recent transfer results using thermal release tape (TRT), [27][28][29] poly(bisphenol A carbonate) (PC), 30, 31 and sacrificial polymer release layers 26 required elevated temperature (over 100°C) during transfer and differed considerably in terms of surface contamination and graphene area coverage. To exploit the intrinsic properties of large-area graphene, a room temperature transfer process that comes off more cleanly than the established methods is needed. In print atIn this study, we compare the transfer of graphene with the conventional PMMA polymer scaffold with alternative poly(lactic acid) (PLA), poly(phthalaldehyde) (PPA), PC, and bilayer PMMA/PC scaffolds. We choose both PLA and PPA as scaffolds as they can supposedly be removed by modest heating or acid exposure. Further, we choose PC from its heightened reactivity as a condensation polymer and it...

Abstract

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.

Depolymerizable polymers are appended with supramolecular cross-linking motifs to enable preparation of tunable single-chain polymeric nanoparticles and degradable polymer networks.