Sunlight photodepolymerization of transient polymers

Abstract

The study and development of transient devices is an emerging field where the disposal of a device after use is desired to avoid reverse engineering and minimize the environmental impact. Polyaldehydes with phototriggers have been investigated because the radiation wavelength can be adjusted to meet the transient application. Polynuclear aromatic hydrocarbons (PAHs) were used as the optical sensitizer for photoacid generators (PAGs). Photoinduced electron transfer (PET) with an iodonium-based PAG was used to expand the spectral sensitivity range. Anthracene, tetracene, and pentacene derivatives were synthesized with appended phenylethynyl groups to improve the solubility of the sensitizer and adjust the absorption wavelength. Sensitization of the iodonium-based PAG with the PAH derivatives was found to have thermodynamically favorable PET reactions for depolymerization of poly(propylene carbonate) and poly(phthalaldehyde) (PPHA). The Rehm-Weller equation and Stern-Volmer analysis were used to study the electron transfer and the fluorescence quenching rates of the PAHs with the iodonium salts, respectively. The photosensitivity, efficiency, and byproducts of the PET reactions in the decomposable polymer films are reported. A rapid photoreaction is reported for the depolymerization of PPHA exposed to a sunlight dose of <6 J cm −2 (i.e., 1 min of direct sunlight) with a pentacene-based sensitizer.

Photodegradable transient bilayered poly(phthalaldehyde) with improved shelf life

“…Bilayer PPHA films were prepared by laminating two PPHA film layers using solvent bonding. Bilayer PPHA films were then exposed at a total dose of 3.6 J/cm 2 from a Xe lamp to ensure complete activation of the PAGs . This dose was chosen because it is greater than the minimum dose needed for full PAG activation.…”

“…PPHA degradation can be triggered by different types of stimuli. These include photochemical (eg, visible light, light emitting diode, and ultraviolet), chemical, thermal, and mechanical stimulus . Visible light stimulus is particularly attractive because of the availability of ambient light.…”

“…Visible light stimulus is particularly attractive because of the availability of ambient light. Phillips et al demonstrated the use of a photo‐induced electron transfer (PET) reaction between a fused‐aromatic‐ring sensitizer and photoacid generator (PAG) to create a strong acid that led to PPHA degradation using visible light . Anthracene (λ max = 370 nm) was modified to form 1,8‐dimethoxy‐9,10‐bis(phenylethynyl)anthracene (DMBA, λ max = 476 nm and 504 nm) allowing a broader wavelength of light to be harvested, resulting in a faster rate of degradation in sunlight …”

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

“…The continuous insertion mechanism of monomer, ortho-phthalaldehyde (oPA), into the cyclic structured PPHA, as described in ref. [26] Figure 2b explains the reaction mechanism of PiET reaction. The acetal linkage on the PPHA backbone is highly susceptible to strong acid attack to result in ring-opening of cyclic structure.…”

“…[24], ensured the formation of high molecular PPHA until the reaction equilibrium was achieved. [26,27] This redox reaction resulted in the homolytic cleavage of PAG and formation of strong superacid that can rapidly depolymerize the film. [25] Upon ring-opening of cyclic PPHA, the end-group unprotected PPHA would rapidly depolymerize back to oPA due to its low ceiling temperature nature.…”