Photodegradable transient bilayered poly(phthalaldehyde) with improved shelf life

Abstract

Metastable poly(phthalaldehyde) (PPHA) can be triggered to depolymerize under visible light by incorporation of photosensitive compounds, such as a photoacid generator (PAG), which can generate a strong acid in situ. However, photosensitive compounds can be thermally unstable and have limited shelf life, causing inadvertent device triggering. It can also be difficult to fabricate components that are photosensitive because special lighting conditions are needed. In this paper, nonphotosensitive PPHA films were formed and made photosensitive at the point of use. This improved the material shelf life and manufacturability by adding a second, PAG‐containing layer to the original nonphotosensitive layer at an optimal point before use. The catalytic photoacid was generated rapidly by exposure of the PAG‐containing layer to radiation. Depolymerization of PPHA via the acid catalyst was followed by diffusion of the acid into the nonphotosensitive layer causing it to depolymerize. Diffusion of the photoacid into the nonphotosensitive medium was quantified at various temperatures. Photoacid diffusion in a liquid, moving‐front caused depolymerization of the nonphotosensitive PPHA layer. The fabricated bilayer structure allowed for better stability of the structural material using PPHA while still achieving transience.

Sunlight‐Triggerable Transient Energy Harvester and Sensors Based on Triboelectric Nanogenerator Using Acid‐Sensitive Poly(phthalaldehyde)

“…The acetal linkage on the PPHA backbone is highly susceptible to strong acid attack to result in ring-opening of cyclic structure. [28][29][30] Moreover, IL enhances the transient property, due to its good solubility of oPA monomers, resulting in formation of liquid byproducts that can be absorbed into the surrounding environment. In this study, a superacid (i.e., pK a less than that of 100% pure sulfuric acid) was in-situ produced upon exposure to UV/visible light using photo-induced electron transfer (PiET) reaction mechanism between anthracene and Rhodorsil FABA.…”

“…The neat oPA monomer was investigated as well to find the expected spectrum of depolymerized product. [30] TENG has been proven to be an effective tool in characterizing the triboelectric performance, or the ability of capturing surface charges during triboelectrification, of materials. The small peak at around 1720 cm −1 corresponded to the carbonyl stretching from carboxylate group from phthalic acid.…”

Photo‐Induced Depolymerisation: Recent Advances and Future Challenges

“…For example, when triggering moieties were incorporated at the chain ends of SIPs, a spontaneous head‐to‐tail depolymerisation would occur after being activated by the corresponding stimuli as shown in Figure A. For self‐immolative block polymers, the accurate cleavage of targeted photosensitive groups for drug release under light irritation has been achieved . Recently, Kohl et al .…”

Time‐delayed photo‐induced depolymerization of poly(phthalaldehyde) self‐immolative polymer via in situ formation of weak conjugate acid

“…A specific‐ion coactivation effect at the surface of cyclic PPHA microcapsules has been shown to accelerate depolymerization in acidic methanol solution . Photo‐acid generators (PAGs) have also been used to trigger PPHA depolymerization via sunlight and other radiation sources . The PAG spectral response has been extended to include the entire visible spectrum for sunlight or targeted wavelength exposure .…”

“…17 Photo-acid generators (PAGs) have also been used to trigger PPHA depolymerization via sunlight and other radiation sources. 2,8,18,19 The PAG spectral response has been extended to include the entire visible spectrum for sunlight or targeted wavelength exposure. [20][21][22] The use of a photoinduced electron transfer (PET) reaction between a chemical sensitizer and PAG to create a strong acid in situ upon exposure to visible light is of particular interest because it opens up device applications where visible light is available upon mission completion.…”